WO2017005628A1

WO2017005628A1 - A light-based sebum and water level measurement system for skin

Info

Publication number: WO2017005628A1
Application number: PCT/EP2016/065513
Authority: WO
Inventors: Babu Varghese; Hendrik Halling Van Amerongen; Martin Jurna; Jonathan Alambra PALERO; Margaret Ruth HORTON; Anna EZERSKAYA
Original assignee: Koninklijke Philips N.V.
Priority date: 2015-07-03
Filing date: 2016-07-01
Publication date: 2017-01-12

Abstract

The invention provides a measurement system (110) for simultaneous light-based measurement of sebum and water levels in skin (160) using a suitable light source and at least three light intensity detectors to detect the intensity of light reflected (145) from the skin, i.e. a first detector (150) detecting a first light intensity in a first detection wavelength range, a second detector (250) detecting a second light intensity in a second detection wavelength range, and a third detector (350) detecting a third light intensity in a third detection wavelength range. The first, second and third detection wavelength ranges each have a maximum extension of 20 nm, wherein the first detection wavelength range comprises a wavelength for which an absorption coefficient for light of sebum is significantly higher than an absorption coefficient for light of water, the second detection wavelength range comprises a wavelength for which the absorption coefficient for light of sebum and the absorption coefficient for light of water are approximately equal, and the third detection wavelength range comprises a wavelength for which the absorption coefficient for light of water is significantly higher than the absorption coefficient for light of sebum. The measurement system (110) is further configured to determine a first parameter associated with a sebum level and a second parameter associated with a water level of the skin based on the first light intensity, the second light intensity and the third light intensity. By using an optical system for simultaneously measuring both the sebum and the water level in skin, said levels may be determined without or with minimum skin contact at approximately the same position in the skin. Additionally, the simultaneous measurement of water and sebum levels allows a more accurate and faster measurement compared to measurement systems known in the art.

Description

A LIGHT-BASED SEBUM AND WATER LEVEL MEASUREMENT SYSTEM FOR SKIN

FIELD OF THE INVENTION

The invention relates to a measurement system for simultaneous light-based measurement of sebum and water levels in skin.

The invention further relates to a skin treatment system for supplying a substance for increasing a sebum level and/or a water level of skin, comprising the measurement system according to the invention.

The invention also relates to a skin treatment system for treatment of skin by means of energy, comprising the measurement system according to the invention.

BACKGROUND OF THE INVENTION

Levels of skin sebum (skin surface lipids) and water (also called skin moisture or skin hydration) in skin are considered important factors in skin health. A right balance between these components is an indication of healthy skin and plays a central role in protecting and preserving skin integrity. An optimal balance between sebum and water levels in skin provides the skin with a radiant, smooth texture and a natural pigmentation appearance, which is important from a cosmetic perspective.

The water and sebum retaining ability of skin is primarily related to the stratum corneum (SC). The SC forms a barrier to water loss, and comprises corneocytes and an intercellular lipid bilayer matrix. The water-retaining property of the SC depends on two major components, i.e. the presence of natural hygroscopic agents, collectively referred to as natural moisturizing factor (NMF), and the SC intercellular lipids, orderly arranged to form a barrier to prevent trans-epidermal water-loss (TEWL).

Skin sebum is a mixture of fatty acids, triglycerides, proteins, and other molecules produced by the sebaceous glands in the dermis. Sebum keeps skin smooth and flexible by sealing and preserving water in the corneal layer and preventing evaporation and bacterial infections. The sebum excretion rate (SER) reflects the amount of sebum production and is closely related to the physiological activities of the sebaceous glands. This is important information in the pathogenesis of sebaceous glands disorders, such as pimples and acne. Excessive sebum production can cause clogged pores possibly resulting in blemishes.

Sufficient levels of water and sebum in the skin make the skin appear smooth, soft and supple, whereas a lack of water can cause the skin to look dull and cracked, appearing older. Good moisturizing creams have an optimal blend of the right barrier building, for example, TEWL-reducing lipids combined with a good humectant delivery system. Significant reduction in the efficiency of the barrier, and thus in the water- maintaining functions of the skin, results in easily dried, roughened skin which can be potentially more vulnerable to risk of infection. Such problems are known in the art. For example, see Woo, Ahn, Chun and Kim, "Development of a Method for the Determination of Human Skin Water Using a Portable Near-Infrared System", Anal. Chem., 73, pp. 4964- 4971(2001).

To address both medical and cosmetic needs, several independent biophysical methods and devices have been developed for monitoring and influencing the amount of sebum and water in human skin. The most well-established commercially available water level meters measure electrical properties, such as capacitance and alternating current conductivity, on the skin surface. Presently available sebum level measuring devices are based on grease-spot photometry and gravimetric analysis. These devices need to be in contact with the skin and are tedious and time-consuming.

TEWL, expressed in grams per square meter and per hour, is commonly used for studying the water barrier function of human skin. However, the method is very sensitive to environmental changes, and requires several minutes to retrieve stable readings. The most commonly used skin water measuring devices are Skicon®200, Corneometer® CM820, Nova DPM® 9003. These devices need to be in contact with the skin and use rigid probes. Furthermore, the measurements are influenced by the amount of electrolytes, the contact area, the applied pressure, and are sensitive to external temperature and humidity

fluctuations. They are not suitable for measuring changes in the water levels over time, and not suitable for visualizing the spatial distribution and heterogeneity of the skin moisturizing- ability of the whole face. See, for example, the problems discussed in Omar, Fairuz, and MatJafri "Optical Fiber Near Infrared Spectroscopy for Skin Water Measurement", Selected Topics on Optical Fibre Technology, Intech/Rijeka, 229-246 (2012).

Optical methods have also been developed to measure water and sebum levels in skin. For example, US 2004/0086456 discloses an optical sebum sensing device using LED illumination and a photometric sensor. Sebum increases the amount of light reflected from the skin, which is collected by a sensor giving a relative value for the sebum level. The more sebum is present on the skin surface, the more light is reflected by the skin surface to the sensor. In this method, the device is in contact with the skin, and it gives a relative value for the sebum level. The measurements can be influenced by variation in water levels.

Near-infrared (NIR) multispectral imaging is an optical method that measures water levels in the skin based on the prominent water absorption peaks in the reflectance spectrum. However, in devices where a single wavelength is used, the measured values for the water level are influenced by the presence of other chromophores.

In methods which use shorter wavelengths, the absorption of water is very low while the scattering is high, resulting in a higher influence of light scattering on the measured water levels as disclosed in the paper by Omar, Fiaruz and MatJafri mentioned above.

In order to correct for the influence and artefacts arising from other chromophores, an analytic method based on the difference in absorbance of two NIR wavelength bands (1060 nm and 1450 nm) has been reported in Iwasaki, Miyazawa and Nakauchi, "Visualization of the human face skin moisturizing-ability by spectroscopic imaging using two near-infrared bands", Spectral Imaging: Eighth International Symposium on Multispectral Color Science, Proceedings of SPIE-IS&T Electronic Imaging, SPIE Vol. 6062 (2006).

BE1017986 describes a non-invasive process for estimating the ratio between fat content and water content of a substance, preferably animal tissues, to deduce the fat mass and the lean mass, which process comprises simultaneously measuring three infrared lines radiated and injected into the substance or tested tissues, by comparing the direct absorption (transmission) or indirect (reflection-diffusion). Further, this document describes a noninvasive process for estimating the ratio between fat content and water content of a substance, preferably animal tissues, and deducing the fat mass and the lean mass, the process comprising simultaneously measuring three infrared lines radiated and injected into the substance or tested tissues, by comparing the direct absorption (transmission) or indirect (reflection-diffusion), where the: first line is related to lipid and located at 930 nm +- 15 nm; second line is related to water and located at 970 +- 40 nm; third line is the standard line located outside of absorption peak of analyzed elements e.g. 850 nm for animal flesh; and +- represents the spectral window in which a line can be selected.

US2008/221406 describes a system and a method for measuring a water reserve index. The method includes determining a lean water fraction of tissue for at least one tissue site and determining skin thickness for the at least one tissue site. The lean water fraction and skin thickness are combined to produce a water reserve estimate.

US7620212 describes methods and systems that extend the functionality of electro-optical sensors. A device has a multiple light sources, a light detector, and a processor configured to operate the light sources and the light detector to perform distinct functions. At least one of the distinct functions includes a biometric identification function in which light is propagated from the plurality of light sources through presented material. The propagated light is received with the light detector, with the presented material being identified from the received light. Another of the distinct functions includes a non-identification function performed with the light sources and the light detector.

In summary, in all the optical methods reported above, the device needs to be in contact with the skin, and the results are influenced by various factors such as wavelength- dependent scattering effects and the presence of other chromophores. OBJECT OF THE INVENTION

It is an object of the invention to provide a measurement system for simultaneous light-based measurement of sebum and water levels in skin which is less complex and which provides more accurate and repeatable measurement results. SUMMARY OF THE INVENTION

A first aspect of the invention provides a measurement system for simultaneous light-based measurement of sebum and water levels in skin. A second aspect of the invention provides a skin treatment system.

In an aspect, the invention provides a measurement system for simultaneous light-based measurement of sebum and water levels in skin, the measurement system comprising:

an optical system having a light source configured and arranged to emit a light beam having a source wavelength range;

the optical system being configured and arranged to direct the light beam towards the skin;

the measurement system further configured and arranged to detect a first light intensity within a first detection wavelength range of light reflected from the skin, configured and arranged to detect a second light intensity within a second detection wavelength range of light reflected, and configured and arranged to detect a third light intensity within a third detection wavelength range of light reflected from the skin;

wherein:

the first, second and third detection wavelength ranges each have a maximum extension of 20 nm;

- the first detection wavelength range comprises a wavelength for which an absorption coefficient for light of sebum is significantly higher than an absorption coefficient for light of water;

the second detection wavelength range comprises a wavelength for which the absorption coefficient for light of sebum is approximately equal to the absorption coefficient for light of water; and

the third detection wavelength range comprises a wavelength for which the absorption coefficient for light of water is significantly higher than the absorption coefficient for light of sebum;

the measurement system further comprising:

a processor configured and arranged to determine a first parameter associated with a sebum level and a second parameter associated with a water level of the skin based on the first light intensity, the second light intensity and the third light intensity.

In specific embodiments, the measurment system comprises a first detector configured and arranged to detect a first light intensity within a first detection wavelength range of light reflected from the skin;

a second detector configured and arranged to detect a second light intensity within a second detection wavelength range of light reflected from the skin;

a third detector configured and arranged to detect a third light intensity within a third detection wavelength range of light reflected from the skin;

the measurement system further comprising:

a processor, coupled to the first detector, the second detector and the third detector, configured and arranged to determine said first parameter associated with a sebum level and said second parameter associated with a water level of the skin based on the first light intensity, the second light intensity and the third light intensity.

Hence, the measurement system according to an aspect of the invention comprises:

an optical system having a light source configured and arranged to emit a light beam having a source wavelength range; the optical system being configured and arranged to direct the light beam towards the skin;

the measurement system further comprising:

a first detector configured and arranged to detect a first light intensity within a first detection wavelength range of light reflected from the skin;

wherein:

the first detection wavelength range comprises a wavelength for which an absorption coefficient for light of sebum is significantly higher than an absorption coefficient for light of water;

the measurement system further comprising:

a processor, coupled to the first detector, the second detector and the third detector, configured and arranged to determine a first parameter associated with a sebum level and a second parameter associated with a water level of the skin based on the first light intensity, the second light intensity and the third light intensity.

The inventors realized that known NIR multispectral imaging methods to measure water levels in the skin could be improved. These known methods use widely- spaced wavelengths where the variation in wavelength-dependent scattering also influences the measurements.

The inventors also realized that, although it is common practice to use different methods for measuring water and sebum levels in the skin, a simpler device may be provided using the same optical principles to measure the sebum and water levels simultaneously. For example, the Triplesense produced by Moritex Schott uses an electrical capacitance measurement for measuring the water level, and uses an optical sensor to measure the amount of reflected light for measuring the sebum level. This device is described in detail in US2004/0086456.

Optical treatments may be advantageous because they are non-invasive, and may even be used without contacting the outer surface of the skin.

Simultaneous measurement of the water and sebum levels in the skin may be advantageous, because selecting an appropriate skin care treatment or skin care product depends on the balance between the volume fraction of skin surface lipids (sebum levels or skin oiliness) and the water level in skin. It is also advantageous to monitor the change in sebum and water levels in the skin during treatment, which is well possible with the measurement system according to the invention. There are currently no devices that can measure both sebum and water levels simultaneously. Also, by using the same optical system, the positions in the skin at which the sebum and water levels are measured coincide to a higher degree than when using different measurement techniques.

For example, the Sebumeter SM815, as disclosed in Soh, "The application of non-invasive skin bioengineering devices for measuring the skin physiology(I)", Korean Edu J Aesthetics, 1 : 177-184 (2003), classifies skin in four categories:

• Oily skin (O) is hydrated with water levels > 50 AU (arbitrary units) and has excessive sebum levels > 70 μg/cm²;

· Oily & Dry skin (OD) has low water levels < 49 AU and excessive sebum levels > 70 μg/cm²;

• Dry skin (D) has low water levels < 49 AU and average sebum levels < 69 μg/cm²; and

• Normal skin (N) has water levels of approximately 50 AU and sebum levels of approximately 70 μg/cm².

In absolute terms, the skin is generally perceived as dry if the water content of the skin's SC drops below 10%.

A further advantage of the simultaneous measurement of the water and sebum levels is that frequent measurements, even real-time measurements, may be made at different locations in the body for the same individual, to more accurately determine and monitor skin treatments. For example, facial skin is less dry compared to the skin of a hand or the lower leg, and doesn't require the same level of humectant concentrations that is used in hand and body lotions. By simultaneously comparing signals from more than one light intensity detector, the measurement system is less sensitive to ambient climatic variations, such as changes in humidity and temperature.

The wavelength ranges detected by the detectors of the measurement system according to the invention are relatively narrow and, preferably, the most important wavelength for detection, for example the sebum absorption peak wavelength, is centralized within the detected wavelength range, i.e. the detected wavelength range extends

symmetrically relative to the most important wavelength for detection. The extension of each detected wavelength range is typically predetermined and/or controlled to exclude adjacent wavelengths which may negatively influence the measurement, but to include the

wavelengths of interest under typical varying conditions. The detected wavelength ranges may also asymmetrically extend relative to the most important wavelengths for detection. According to the invention, the maximum extension of the detection wavelength ranges of the first, second and third detectors is 20 nm, but a wavelength range of 10 nm is even more preferred. Instead of the term "maximum extension" also the term "spectral window" may be applied.

In a preferred embodiment of the measurement system according to the invention, the first detection wavelength range of the first detector is selected from the group consisting of 1720 nm ± 5 nm, 2305 nm ± 5 nm, 1205 nm ± 5 nm and 910 nm ± 5 nm. For these wavelengths the absorption coefficient for light of sebum is significantly higher than the absorption coefficient for light of water. The extension of these wavelength ranges is no more than 10 nm, and the wavelength of interest for the detection, i.e. the absorption peak wavelength of sebum, is centralized within the first detection wavelength range.

In a further embodiment of the measurement system according to the invention, the second detection wavelength range is selected from the group consisting of

1705 nm ± 5 nm, 1733 nm ± 5 nm, 2277 nm ± 5 nm, 2355 nm ± 5 nm, 1 192 nm ± 5 nm, 1218 nm ± 5 nm, 900 nm ± 5 nm and 930 nm ± 5 nm. For these wavelengths the absorption coefficient for light of sebum is approximately equal to the absorption coefficient for light of water. The extension of these wavelength ranges is no more than 10 nm, and the wavelength of interest for the detection, i.e. the wavelength for which the absorption coefficients for light of sebum and water are equal, is centralized within the second detection wavelength range. The second detection wavelength range is used as a reference wavelength at which both chromophores absorbs approximately equally. This allows differential detection. Hence, the measurement system may be configured to to determine the first and second parameter based on differential detection.

In a further embodiment of the measurement system according to the invention, the third detection wavelength range is selected from the group consisting of 1695 nm ± 5 nm, 1770 nm ± 5 nm, 2255 nm ± 5 nm, 2375 nm ± 5 nm, 1 182 nm ± 5 nm, 1221 nm ± 5 nm, 886 nm ± 5 nm and 936 nm ± 5 nm. For these wavelengths the absorption coefficient for light of water is significantly higher than the absorption coefficient for light of sebum. The extension of these wavelength ranges is no more than 10 nm, and the wavelength of interest for the detection, i.e. the absorption peak wavelength of water, is centralized within the third detection wavelength range.

In a further embodiment of the measurement system according to the invention, the first detection wavelength range is 1720 nm ± 5 nm, the second detection wavelength range is 1705 nm ± 5 nm or 1733 nm ± 5 nm, and the third detection wavelength range is 1695 nm ± 5 nm or 1770 nm ± 5 nm. For said first detection wavelength range, the ratio between the absorption coefficients for light of sebum and water is relatively high, while for said third detection wavelength range the ratio between the absorption coefficients for light of water and sebum is relatively high. Because in this embodiment the first, second and third detection wavelength ranges are relatively close to each other, the differences between optical properties of the skin within the first, second and third detection wavelength ranges are relatively small, so that the effect of said differences on the measurement results is limited. In addition, within these detection wavelength ranges, the scattering coefficient of skin tissue, in particular of the dermis, is relatively small, so that the effect of scattering of light on the measurement results is limited, and the measurements can be performed at target positions at a relatively large depth below the skin surface.

In a further embodiment of the measurement system according to the invention, the first detection wavelength range is 2305 nm ± 5 nm, the second detection wavelength range is 2277 nm ± 5 nm or 2355 nm ± 5 nm, and the third detection wavelength range is 2255 nm ± 5 nm or 2385 nm ± 5 nm. Because also in this embodiment the first, second and third detection wavelength ranges are relatively close to each other, the differences between optical properties of the skin within the first, second and third detection wavelength ranges are relatively small, so that the effect of said differences on the measurement results is limited.

In a further embodiment of the measurement system according to the invention, the first detection wavelength range is 910 nm ± 5 nm, the second detection wavelength range is 900 nm ± 5 nm or 930 nm ± 5 nm, and the third detection wavelength range is 886 nm ± 5 nm or 936 nm ± 5 nm. Because also in this embodiment the first, second and third detection wavelength ranges are relatively close to each other, the differences between optical properties of the skin within the first, second and third detection wavelength ranges are relatively small, so that the effect of said differences on the measurement results is limited.

In an embodiment of the measurement system according to the invention, the measurement system is further configured and arranged to polarize light within the source wavelength range, thereby generating a polarized light beam, and to direct the polarized light beam towards the skin, the polarized light beam having a first polarization direction, the measurement system further comprising at least one light filter disposed in a light path of light reflected from the skin to least one of the first, second and third detectors, the light filter being configured to preferentially transmit light having a second polarization direction, wherein the first and second polarization directions are different.

During the measurement, light penetrates the skin and is reflected from the skin surface and from skin layers at different depths below the skin surface. Because this embodiment uses a cross-polarized optical configuration, the measurement system is more sensitive to deeper layers, because light reflected from the upper layers of the skin is transmitted less-preferentially to the detectors. The deepest possible measurement may be achieved when the first and second polarization directions differ by approximately 90 degrees. The depth of the measurement is also affected by the source wavelength range of the light source.

Measurements at deeper positions below the skin surface are advantageous for the purpose of detecting the presence of hyperactive and large-sized sebaceous glands which produce excessive sebum, and detecting skin ducts filled or clogged with sebum. Once detected, these conditions may be treated by delivering an appropriate dose of treatment energy to the skin, such as laser energy for treatment of the glands using the effects of selective photothermolysis.

In the measurement system according to the invention, the processor coupled to the first, second and third detectors may, for example, determine the sebum and water levels based on differential detection of the light intensities measured within the first, second and third detection wavelength ranges. Alternatively, the processor may provide a more accurate calculation, including applying corrections and calibrations. In an embodiment of the measurement system according to the invention, a central wavelength of the source wavelength range is in a range from visible light to infrared light. Particularly, the use of NIR light is advantageous, because NIR light can penetrate relatively deep into skin tissue.

The skin treatment system according to a further aspect of the invention comprises the measurement system according to the invention.

An embodiment of the skin treatment system according to the invention is configured and arranged to supply a substance for increasing a sebum level and/or a water level of skin. In this embodiment, the measurement system provides the first parameter associated with the sebum level in the skin and the second parameter associated with the water level in the skin. In this embodiment, the skin treatment system may be configured and arranged to modify at least one characteristic of the substance to be supplied to the skin based on the first parameter and/or the second parameters. Examples of characteristics of the substance to be modified include the composition, the water content, and the oil content of the substance, the dosage of the substance, the position at which the substance is supplied to the skin, and the duration during which the substance is applied to the skin.

A further embodiment of the skin treatment system according to the invention is configured and arranged for treatment of skin by means of energy. In this embodiment, the skin treatment system comprises an energy source and a supply system for supplying energy generated by the energy source to the skin. In this embodiment, the measurement system provides the first parameter associated with the sebum level in the skin and the second parameter associated with the water level in the skin. In this embodiment, the skin treatment system may be configured and arranged to modify at least one characteristic of the energy to be supplied to the skin based on the first parameter and/or second parameters. Examples of the energy to be supplied for skin treatment include radio-frequency (RF) energy, ultrasound energy and light energy. Examples of characteristics of the energy to be modified include the wavelength and/or frequencies comprised in the energy beam, a pulse duty cycle, a dosage, a position where the energy is supplied to the skin, and a duration during which the energy is supplied. For example, hyperactive sebaceous glands may be treated by means of laser-light energy using the effects of selective photothermolysis.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Fig. 1 schematically shows a measurement system according to the invention; Fig. 2 shows a graph showing the variation of the absorption coefficients for light of both water and sebum at different wavelengths;

Fig. 3 shows a graph showing the variation of the ratio between the absorption coefficients for light of sebum and water at different wavelengths;

Fig. 4 shows a graph showing the variation of the absorption coefficients for light of both water and sebum in the preferred wavelength range between 1675 nm and 1775 nm; and

Fig. 5 shows a graph showing the absorption coefficients for light of human adipose tissue and of two different sebum compositions in the wavelength range between 1000 nm and 2000 nm. DETAILED DESCRIPTION OF THE EMBODIMENTS

Fig. 1 schematically shows a measurement system 1 10 according to the invention. The measurement system 1 10 is configured and arranged for simultaneous light- based measurement of sebum and water levels in skin 160. The measurement system 1 10 comprises an optical system 130, which comprises a light source 120 for emitting light over a predetermined and/or controlled source wavelength range.

The light source 120 is preferably a polychromatic source which comprises a relatively broad spectrum of wavelengths. In other words, it is preferably polychromatic or broadband or "white". The skilled person may use techniques known in the art to determine the optimal source wavelength range or bandwidth, using a plurality of light sources simultaneously, or a broadband light source in combination with one or more suitable bandpass filters. Light is used here as a general term for electromagnetic radiation that can penetrate into skin, and may include non- visible wavelengths such as IR (infra-red).

Examples of suitable polychromatic or broadband light sources are:

tungsten/arc lamps having an emission spectrum in the range of 1720 - 1770 nm;

a Superluminiscent Laser Diode (SLD) or Light-Emitting Diode (LED) emitting light with a wavelength range comprising at least the first, second and third detection wavelength ranges. Alternatively, the polychromatic or broadband source may comprise two or more monochromatic (or narrow-band) sources, operated simultaneously, for example a first, second and third monochromatic light source, each having a spectral emission wavelength range comprising a respective one of the first, second and third detector wavelength ranges. Hence, the term "light source" may also refer to a plurality of (different) light sources.

The optical system 130 further comprises optical elements such that the light beam from the light source 120 exits the measurement system 1 10 during use and is directed 140 towards a target position in the skin. The skilled person may select any combination of light source and optical elements known in the art to achieve this, and may predetermine and/or control the position and size of the target position. The light beam 140 may be configured and arranged to penetrate the skin to the desired depth below the skin surface, proximate the desired target position. The water and sebum levels may be relatively constant over an area of skin, or they may change abruptly. For example, an overactive sebaceous gland may produce a relatively small area with an increased sebum level. The variation in levels may be location dependent within the body, and may change from person to person.

The measurement system may be further configured and arranged to select the position and size of the target position being targeted by the light beam and/or the area proximate the target position from which the reflected light is to be detected. In this way, the area of skin for which the sebum and water levels are to be measured may be predefined and/or controlled to provide the required measurement resolution. In some cases, it may be advantageous to measure a relatively small region of skin, and in other cases it may be advantageous to measure relatively large regions. The size of the target position may be influenced by, inter alia, a maximum dimension of a cross-section of the incident light beam proximate the skin, or by scanning the incident light beam.

The measurement sysem may e.g. include a single detector, like a CCD array

(Charge-Ccoupled Device), configured to measure in a plurality of spectral regions, such as defined herein. Hence, the measurment system may include a detector with a pluraltiy of detection channels. The term "detector" may also relate to a plurality of different detectors. Herein, especially embodiments are described with different detectors or detectors with different upstream optics, such that different wavelength ranges can be detected.

Amongst others, the measurement system may include one or more detectors as described in US7620212: for instance, the detector(s) can be any material appropriate to the spectral region being detected. For light in the region from about 350 nm to about 1 100 nm, a suitable detector material is silicon and can be implemented as a single-element device, a collection of discrete elements, or a ID or 2D array, depending upon the system

configuration and encoding method used. For light in the region from about 1.25 to about 2.5 μηι, a suitable detector material is InGaAs and can also be implemented as a single element, a collection of elements, or a ID or 2D array. Additional detector materials and means of detection include InSb, Ge, MCT, PbS, PbSe, bolometers, and others known to one of ordinary skill in the art.

The measurement system 1 10 further comprises a first detector 150, a second detector 250 and a third detector 350. The measurement system 1 10 is further configured to direct light 145 reflected from the region of skin proximate the position of incidence on the skin 160 to all three detectors 150, 250, 350. Light will be reflected not only by the upper surface of the skin, but also by deeper layers of the skin. The measurement system further comprises one or more optical members known in the art to achieve this result, such as two 50/50 beamsplitter and a folding mirror which is depicted in Fig. 1. As the sebum and water level measurement may be determined by comparing the light intensity measurements by the first detector 150, the second detector 250, and the third detector 350, it may be advantageous to configure the beam paths between the skin surface and the detectors 150, 250, 350 so as to be as equal as possible.

The first detector 150 is configured and arranged to detect a first light intensity within a first detection wavelength range of the light 145 reflected from the skin, the second detector 250 is configured and arranged to detect a second light intensity within a second detection wavelength range of the light 145 reflected from the skin, and the third detector 250 is configured and arranged to detect a third light intensity within a third detection wavelength range of the light 145 reflected from the skin. To achieve this, each detector may for example be preceded by a suitably configured band-pass filter.

A processor, not shown in Fig. 1, is coupled to the first detector 150, the second detector 250 and the third detector 350. The processor is configured and arranged to determine a first parameter associated with a sebum level of the skin and a second parameter associated with a water level of the skin based on the light intensities detected by the first, second and third detectors 150, 250, 350.

The measurement system 1 10 is configured to measure sebum levels and water levels in skin proximate the position impinged by the incident light. This includes

predetermining and/or controlling the first detection wavelength range, the second detection wavelength range and the third detection wavelength range. These wavelength ranges may be determined experimentally by measurements on a wide range of subjects and skin regions, or by computer simulation for a chosen focus depth.

The detection wavelength ranges are mainly selected based upon the ratio between the absorption coefficients for light of sebum and water, water being the main component of moisture in the skin. To determine the levels of sebum and water in the skin, three detection wavelength ranges are required:

• a first wavelength range (or value) comprising a wavelength for which the absorption coefficient for light of sebum is significantly higher than the absorption coefficient for light of water;

· a second wavelength range (or value) comprising a wavelength for which the absorption coefficient for light of sebum is approximately equal to the absorption coefficient for light of water; and

• a third wavelength range (or value) comprising a wavelength for which the absorption coefficient for light of water is significantly higher than the absorption coefficient for light of sebum.

In practice, it is advantageous to use a wavelength range around each of the preferred wavelength values to provide a higher degree of reproducibility and stability in the measurement. In short, there are four wavelengths for which the absorption coefficient of sebum is higher than the absorption coefficient of water, namely approximately 910 nm, 1205 nm, 1720 nm and 2305 nm. For many other wavelengths, water absorbs light better than sebum.

A second factor, that is preferably to be taken into account when selecting the detection wavelength ranges, is the additional losses caused by scattering and absorption of light by skin tissue and other chromophores present in the skin. These effects are relatively strong at lower wavelengths, causing said approximate wavelengths of 1720 nm and 2305 nm to be most preferred. The effects of scattering and absorption by skin tissue and

chromophores on the measurement results are further reduced by selecting the three wavelength ranges (or values) to be close to each other.

A third factor, that is to be preferably taken into account when selecting the detection wavelength ranges, is the depth of penetration of the light beam 140 into the skin tissue. The penetration depth of light at approximately 1720 nm is around 1 mm, and for light at approximately 2305 nm it is around 400 μηι. For deeper measurements, approximately 1720 nm is therefore the preferred wavelength value. Although sebum composition varies from person to person, the approximate wavelengths where absorption of light by sebum is highest and lowest are relatively stable.

Sebum is a mixture of free fatty acids, triglycerides, sterol, cholesterol, wax ester, and hydrocarbons. The percentage of these individual components and the saturated and unsaturated volume fractions are known to vary as disclosed in Motwani, Rhein, and Zatz, "Differential scanning calorimetry studies of sebum models", Journal of Cosmetic science, 2010, 52, 21 1 -22.

However, the absorption spectrum of sebum exhibits maxima (or peaks) at their respective prominent wavelengths due to the presence of certain bonds. Without wishing to be bound by theory, it is believed that:

• the presence of the C-H and C-C bonds accounts for the 2305 nm absorption peak;

• a first overtone caused by the C-H bond accounts for the 1720 nm absorption peak;

· a second overtone caused by the C-H stretch in the chains of the free fatty acids, the triglycerides & the wax esters, and in the C-H stretch in the aromatic ring of the sterol and cholesterol, accounts for the 1205 nm absorption peak;

• a third overtone caused by the C-H bond accounts for the absorption peak at 910 nm.

These bonds and overtones are further described in Chung, Kim, "Near-

Infrared Spectroscopy: Principles", Analytical science & Technology, 2000, 13 (1); Law, Tkachuk, "Near infrared diffuse reflectance spectra of wheat and components", Cereal Chemistry Journal, 1976, 54(2): 256-265; and Workman, Weyer, "Practical Guide to Interpretive Near-Infrared Spectroscopy", CRC Press, 2007. 344.

To verify the stability of the wavelengths associated with the absorption maxima and minima for sebum, the inventors tested two different artificial sebum samples and human adipose tissue in the spectral range of 400 nm to 2000 nm. The compositions were as follows: · Adipose tissue:

27% free fatty acids

32% triglycerides

16% sterol

0% cholesterol 25% wax ester

0% hydrocarbon mixture

• Artificial sebum 1 :

27.6% free fatty acids, of which 13.8%) were saturated and 13.8%) were unsaturated

32.1 %) triglycerides, of which 21 .4% were saturated and 10.7% were unsaturated

10.3% sterol

3.9%o cholesterol

26.1 %o wax ester, of which 20.2% were saturated and 5.9% were unsaturated 0% hydrocarbon mixture

• Artificial sebum 2:

50.8%) free fatty acids, of which 22.8% were saturated and 28% were unsaturated

3.6%o triglycerides

0% sterol

3.7%o cholesterol

29.9%o wax ester

12% hydrocarbon mixture

Fig. 5 depicts the measured absorption coefficient, plotted as absorption coefficient from 0 to 12 cm^"1 along the vertical axis 510 against the wavelength from 1000 to 2000 nm along the horizontal axis 520.

The human adipose tissue absorption spectrum 545 graph indicates about 6 cm^"1 at approximately 1770 nm, about 1 1 cm^"1 at approximately 1720 nm, about 1 cm^"1 at approximately 1400 nm, and about 1 .9 cm^"1 at approximately 1200 nm. The artificial sebum 2 absorption spectrum 535 graph indicates about 6 cm^"1 at approximately 1770 nm, about 1 1 cm^"1 at approximately 1720 nm, about 1 .8 cm^"1 at approximately 1400 nm, and about 2 cm^"1 at approximately 1205 nm. The artificial sebum 1 absorption spectrum 525 graph indicates about 6 cm^"1 at approximately 1770 nm, about 1 1 cm^"1 at approximately 1720 nm, about 1 .9 cm^"1 at approximately 1400 nm, and about 2 cm^"1 at approximately 1205 nm. The spectra 525, 535, 545 overlap to a very high degree with the two artificial sebum spectra 525, 535 being indistinguishable for most of the frequency range, and the human adipose tissue spectrum 545 displaying slightly lower minima.

In all three cases, the prominent absorption peak is around 1720 nm, and at the other expected wavelengths. For this experimental set-up, it was necessary to combine the two available spectrometers to obtain the range of 400 -2000 nm. For the wavelengths below 1000 nm no absorption peaks were found, although an absorption peak was expected at approximately 910 nm. It is believed that this absorption peak would be detected with more sensitive equipment, and would also show a high degree of overlap between the spectra. Measurements above 2000 nm were not possible, but it is believed that the absorption peak at approximately 2305 nm would be detected by using an extended spectrometer, and would also show a high degree of overlap between the spectra.

Fig. 2 depicts the measured coefficient of absorption, plotted logarithmically as absorption coefficient from 0.1 to 30 cm^"1 along the vertical axis 210, and plotted linearly as wavelength from 800 to 2200 nm along the horizontal axis 220. Two absorption spectra are depicted, i.e. a spectrum for water 225 and a spectrum for sebum 235. The sebum spectrum 235 depicts absorption peaks at about 1200 nm & 2 cm^"1, 1400 nm & 1.5 cm^"1, and 1720 nm & 10cm^"1. The sebum spectrum 235 also depicts troughs at about 1 100 nm & 0.3cm^" ^l, 1300 nm & 0.35cm^"1, 1570 nm & 0.65cm^"1, and 2000 nm & 3cm^"1. The water spectrum 225 depicts absorption peaks at about 960 nm & 0.8cm^"1, 1 175 nm & 1.8cm^"1, 1410 nm & 1 1cm^"1, and 2000 nm & 25 cm^"1. The water spectrum 225 also depicts troughs at about 880 nm & 0.3 cm^"1, 1060 nm & 0.5cm^"1, 1280 nm & 1.5cm^"1, and 1680 nm & 5cm^"1.

Intersections between the water spectrum 225 and the sebum spectrum 235 are depicted at about 930 nm & 0.45 cm^"1, 1 192 nm & 1.3 cm^"1 , 1218 nm & 1.3 cm^"1 , 1705 nm & 5.4 cm^"1 , and 1750 nm & 8 cm^"1 .

Fig. 3 depicts the ratio between the coefficients of absorption ratio of sebum and water, plotted from 0 to 1.5 along the vertical axis 310, and plotted as wavelength from 800 to 2400 nm along the horizontal axis 320.

The ratio 325 between the absorption coefficients of sebum and water depicts troughs, where the absorption coefficient of water is higher than the absorption coefficient of sebum. These troughs are at about 936 nm & 0.4, 1 182 nm & 0.4, 1500 nm & 0.05, and 2255 nm & 0.5.

The ratio 325 between the absorption coefficients of sebum and water depicts peaks, where the absorption coefficient of sebum is higher than the absorption coefficient of water. These peaks are at about 910 nm & 1.0, 1060 nm & 0.8, 1205 nm & 1.4, 1720 nm & 1.7, and 2305 nm & 1.7.

The ratio between the absorption coefficients of sebum and water is approximately 1.0 at about 900 nm, 1 192 nm, 1218 nm, 1705 nm, 1750nm, and 2277nm.

Operation of the measurement system according to the invention requires three detection points to be predetermined and/or controlled:

a first wavelength range (or value) comprising a wavelength for which the absorption coefficient for light of sebum is significantly higher than the absorption coefficient for light of water;

a second wavelength range (or value) comprising a wavelength for which the absorption coefficient for light of sebum is approximately equal to the absorption coefficient for light of water; and

a third wavelength range (or value) comprising a wavelength for which the absorption coefficient for light of water is significantly higher than the absorption coefficient for light of sebum.

The first detection wavelength range is preferably a wavelength range comprising a wavelength for which the ratio between the absorption coefficients for light of sebum and water is equal to or greater than 1.2, more preferably equal to or greater than 1.4. The first detection wavelength range may be determined by selecting a suitable position on the graph of Fig. 3, or by experiment and/or simulation. Any wavelength for which the absorption coefficient for light of sebum is at least 20% higher than the absorption coefficient for light of water is considered as a wavelength for which the absorption coefficient for light of sebum is significantly higher than the absorption coefficient for light of water.

The second detection wavelength range is preferably a wavelength range comprising a wavelength for which the ratio between the absorption coefficients for light of sebum and water is approximately 1.0. The second wavelength range may be determined by selecting a suitable position on the graph of Fig. 3, or by experiment and/or simulation. Any wavelength for which the ratio between the absorption coefficients of sebum and water coefficient is from 0.8 to 1.2, more preferably from 0.9 to 1.1, is considered as a wavelength for which the absorption coefficient for light of sebum is approximately equal to the absorption coefficient for light of water. In other words, any wavelength for which the absorption coefficient for light of sebum deviates by no more than 20% from the absorption coefficient for light of water is considered as a wavelength for which the absorption coefficient for light of sebum is approximately equal to the absorption coefficient for light of water.

The third detection wavelength range is preferably a wavelength range comprising a wavelength for which the ratio between the absorption coefficients for light of sebum and water is equal to or smaller than 0.8, more preferably equal to or smaller than 0.6. The third detection wavelength range may be determined by selecting a suitable position on the graph of Fig. 3, or by experiment and/or simulation. Any wavelength for which the absorption coefficient for light of water is at least 20% higher than the absorption coefficient for light of sebum is considered as a wavelength for which the absorption coefficient for light of water is significantly higher than the absorption coefficient for light of sebum.

Based on measurement and simulation results, the following wavelength ranges are preferred:

1. Penetration of light into the skin until a depth of approximately 1 mm

Option A

First detection wavelength range (sebum > water): 1720 nm ± 5 nm;

Second detection wavelength range (sebum = water): 1705 nm ± 5 nm;

Third detection wavelength range (water > sebum): 1695 nm ± 5 nm. Option B

First detection wavelength range (sebum > water): 1720 nm ± 5 nm;

Second detection wavelength range (sebum = water): 1733 nm ± 5 nm;

Third detection wavelength range (water > sebum): 1770 nm ± 5 nm.

2. Penetration of light into the skin until a depth of approximately 400 μηι:

Option A

First detection wavelength range (sebum > water): 2305 nm ± 5 nm;

Second detection wavelength range (sebum = water): 2277 nm ± 5 nm;

Third detection wavelength range (water > sebum): 2255 nm ± 5 nm. Option B

• First detection wavelength range (sebum > water): 2305 nm ± 5 nm;

• Second detection wavelength range (sebum = water): 2355 nm ± 5 nm;

• Third detection wavelength range (water > sebum): 2385 nm ± 5nm.

3. Penetration of light into skin until shallow depths:

Option A

• First detection wavelength range (sebum > water): 910 nm ± 5 nm;

· Second detection wavelength range (sebum = water): 900 nm ± 5nm;

• Third detection wavelength range (water > sebum): 886 nm ± 5 nm.

Option B

• First detection wavelength range (sebum > water): 910 nm ± 5 nm;

· Second detection wavelength range (sebum = water): 930 nm ± 5 nm;

• Third detection wavelength range (water > sebum): 936 nm ± 5 nm.

Although any depth may be used, the longer wavelengths are preferred because they are influenced to a lesser extent by skin scattering. The skilled person may further use trial and error to determine the most appropriate wavelength ranges.

Fig. 4 depicts the variation of the absorption coefficient of both water and sebum in the preferred wavelength range of 1675 to 1775 nm. The absorption coefficient is plotted along the vertical axis 410 from 0 to 10.00 cm^"1, and the wavelength is plotted along the horizontal axis 420 from 1675 to aboutl 800 nm.

The absorption spectrum of water 425 shows a gradual increase from approximately 7.5 cm^"1 at 1675 nm to approximately 9 cm^"1 at approximately 1800 nm.

The absorption spectrum of sebum 435 shows an increase from approximately 2 cm^"1 at 1675 nm to a maximum of approximately 10 cm^"1 at approximately 1720 nm. The spectrum 435 decreases to a minimum of approximately 7 cm^"1 at approximately 1733 nm, rises again to a maximum of 7cm^"1 at 1750 nm, and then falls to about 4.3cm^"1 at 1800 nm. At 1770 nm, the absorption coefficient of sebum is approximately 6 cm^"1.

The scattering coefficient in cm^"1 for the dermis 445 is also plotted. This, however, remains a relatively straight line from 3 cm^"1 at 1675 nm to approximately 2.9 cm^"1 at approximately 1800 nm. In this preferred wavelength range, the scattering coefficient 445 is significantly lower than the absorption coefficients of both water 425 and sebum 435, making measurement more reliable.

Also depicted in Fig. 4 are three points where the sebum absorption spectrum 435 and the water absorption spectrum 425 intersect, namely where the absorption coefficients of sebum and water are approximately equal. These are 7cm^"1 at 1705 nm, 8 cm at 1733 nm, and 7 cm^"1 at 1750 nm.

The measurement system further comprises a processor, coupled to the first detector 150, the second detector 250 and the third detector 350, configured and arranged to determine a first parameter associated with a sebum level and a second parameter associated with a water level of the skin, proximate to the position where the incident light beam 140 impinges on the skin, based on the first light intensity, the second light intensity and the third light intensity measured by, respectively, the first detector 150, the second detector 250 and the third detector 350. The processor functions may be implemented by any suitable analog or digital hardware, or a combination of analog and digital hardware. The first and second parameters may be determined by comparing the first, second and third light intensities. In some embodiments, it may be sufficient to simply detect the difference between these light intensities. In other more complex embodiments, where a higher degree of accuracy is required, the processor may be programmed to determine the first and second parameters based on more complex calculations.

For example, a basic measurement system may be configured to only determine whether the skin proximate the position where the incident light impinges on the skin is approximately OD, O, N or D type. This may be presented to the user using a simple display with, for example, 4 lamps or LED's.

In a further embodiment, merely indicating the presence of a measurable level of water and sebum may be sufficient.

Additionally or alternatively, each intensity measurement may be compared to previous measurements or a reference parameter set, to determine the point in a course of treatment based on the change in water and sebum levels in the skin.

It is not always necessary to measure absolute levels of sebum and water. For example, during some skin treatments, water may be lost from the skin. In such a case, it is sufficient to detect a change in the light intensities during treatment to determine when a threshold has been reached. The measurement system may also comprise means for the user to enter an absolute value of sebum and water level measured by other means. For example, a level of sebum Qs and a level of water Qw may be determined by comparing the light intensities measured at the three wavelengths ranges (or values) based on the following empirical formulas:

Qs is proportional to Itl - (It2/2)

Qw is proportional to It3 - (It2/2) wherein:

Itl is the light intensity detected by the first detector 150, i.e. at the first wavelength range or value for which the absorption coefficient for light of sebum is significantly higher than the absorption coefficient for light of water. A relatively high first light intensity indicates a relatively low level of sebum, and a relatively low first light intensity indicates a relatively high level of sebum.

It2 is the light intensity detected by the second detector 250, i.e. at the second wavelength range or value for which the absorption coefficient for light of sebum is approximately equal to the absorption coefficient for light of water.

It3 is the light intensity detected by the third detector 350, i.e. at the third wavelength range or value for which the absorption coefficient for light of water is significantly higher than the absorption coefficient for light of sebum. A relatively high third light intensity indicates a relatively low level of water, and a relatively low third light intensity indicates a relatively high level of water.

Here the processor is configured and arranged to compare IT1 with (IT2/2), and to compare IT3 to (IT2/2).

It may be also advantageous for the measurement system 1 10 to comprise a processor, programmed to determine the sebum and water levels by comparing the first, second and third light intensities and/or by comparing values derived from the first, second and third light intensities. The skilled person may program the processor to apply any suitable formulas, comprising the first, second and third light intensities, to determine the water and/or sebum levels, when required using any suitable intermediate steps where the first, second and/or third light intensities are subjected to one or more mathematical operations such as divisions, multiplications, subtractions, additions and/or exponentiations.

The processor may be configured and arranged to determine values of the water and sebum levels with different accuracies making appropriate use of calibrations and optional look-up tables. For example, the decay of photon intensity may be assumed to be exponential according to:

It = Ito · exp -( (Us + Uw) * 2 * Z) wherein:

It is the intensity detected

Ito is the intensity of the incident light on the skin

Us is the absorption coefficient of sebum

Uw is the absorption coefficient of water

In an example, based upon comparing the first, second and/or third light intensities, a level of sebum Qs and a level of water Qw is more quantitatively determined according to:

Qs = ( ln( Itl o / Itl ) - ln( It2₀ / It2 ) ) / 2Z (Usl - Us2)

Qw = ( ln( It3o / It3 ) - ln( It2₀ / It2 ) ) / 2Z (Uw3 - Uw2) wherein:

Z is a depth of penetration of light into the skin

Itl is the first light intensity detected at the first detection wavelength range

(or value)

Itl o is the intensity of the light incident on the skin at the first detection wavelength range (or value)

It2 is the second light intensity detected at the second detection wavelength range or value

It2o is the intensity of the light incident on the skin at the second detection wavelength range (or value)

It3 is the third light intensity detected at the third detection wavelength range or value

It3o is the intensity of the light incident on the skin at the third detection wavelength range (or value)

Usl is the absorption coefficient of sebum at the first detection wavelength range (or value) Us2 is the absorption coefficient of sebum at the second detection wavelength range or value

Uw2 is the absorption coefficient of water at the second detection wavelength range or value

Uw3 is the absorption coefficient of water at the third detection wavelength range or value

From many studies of the skin, the skilled person may collect representative empirical data, and construct look-up tables to complement the light intensity levels measured by the detectors. Alternatively or additionally, calibration steps may be included either before, during or after measurement of the sebum and water levels. Alternatively or additionally, the measurement system 1 10 may comprise additional sensors to determine appropriate values for all necessary parameters.

Optionally, the processor may be provided with additional data such as details concerning the person or body region being treated, or the treatment, for example age, skin color, stage in the treatment, target positions and intensity measurement positions on the body. In the simplest embodiment, these data may be recorded solely for a more detailed reporting. Although not essential to the invention, the data may also be used to increase the accuracy of the sebum and water level measurements if the processor is provided with appropriate calculation algorithms or look-up tables.

In summary, as compared to known measurement systems, the measurement system provides a relatively simple, stable and accurate way of simultaneously measuring the sebum and water levels in skin.

Light reflected from upper layers of the skin may be reduced in favour of light from deeper layers by using a cross-polarized optical configuration. For this purpose, the measurement system 1 10 may be further configured and arranged to polarize light within the source wavelength range to generate a polarized light beam 140 which is directed towards the outer layer of the skin. A filter is disposed in the path of the reflected light between the skin and at least one of the first, second and third detectors 150, 250, 350, the filter being configured to preferentially transmit light having a second polarization direction which is substantially different from a first polarization direction of the light directed to the outer surface of skin. Light is reflected from different depths in the skin, not just from the upper layers and the outer skin surface. The depth of skin most contributing to the water and sebum level measurement may be influenced by modifying the wavelengths comprised in the polarized light beam 140 and by selecting the difference between the first and second polarization directions of the incident light and the light transmitted by said filter. The greatest effects and deepest measurements may be expected when the first and second polarization directions differ by approximately 90 degrees.

The system may also be configured to be more sensitive to light reflected from the upper layers and the outer skin surface by using parallel polarized detection, wherein said first and second polarization directions are approximately equal.

The first, second and third detectors 150, 250, 350 may be any suitable detectors able to determine an intensity of the reflected light. For example, the detectors 150, 250, 350 may be relatively simple photodiodes or any other detector able to detect the intensity of the reflected light, preferably preceded by a suitably selected narrow band-pass filter to select the respective narrow wavelength range for detection. For example, detectors may be used which are sensitive to IR wavelengths, such as InGaAs, InP or PbS detectors. Filtering of the narrow wavelength band for each detector may be achieved by using any combination of suitable absorptive, reflective or notch filters known in the art. An array of sensors, together with appropriate spectral filters, may also be used to determine the sebum and water levels over a larger area of skin, in other words at a plurality of positions proximate the target position.

Additional optical elements known in the art may also be provided in the optical system 130 to further guide and modify the incident light beam 140 and/or the reflected light beam 145.

The measurement system 1 10 may be a stand-alone system or device.

However, it may be integrated into a suitable skin treatment system.

For example, it may be comprised in a skin treatment system for supplying a substance to treat the skin by increasing the sebum level and/or the water level of skin.

Advantageously, the measurement system may determine the sebum level and the water level, providing the first parameter associated with the sebum level and the second parameter associated with the water level. Based on the values of the first and second parameters, the skin treatment system modifies the supply of the substance in a particular way to influence the sebum and/or water levels of the skin. The measurement system may even provide realtime feedback for the simultaneous and quantitative monitoring of the sebum and water contents of the skin, in particular when used in combination with an appropriate treatment system, such as a substance supply system. Also, based on the first and second parameter, other treatment parameters of the skin treatment system may be adjusted or optimized to achieve an improved treatment efficacy.

Similarly, the measurement system 1 10 may be comprised in a skin treatment system for supplying energy to skin for skin treatment. In such an application, the measurement system may determine the sebum and a water levels of the skin, thereby providing the first parameter associated with the sebum level and the second parameter associated with the water level. Based on the first and second parameters, the skin treatment system modifies at least one characteristic of the energy to be supplied to the skin. In such an energy-based skin treatment system, skin safety is a major concern. The possibility to monitor the sebum and water levels simultaneously means that the treatment efficacy of the skin treatment system may be continuously optimized, so that dangerous conditions may be avoided. Because the measurement system may operate in a non-contact mode relative to the skin, it is suitable for all types of energy-based skin treatment systems, such as laser-light based systems, RF-based systems, and ultrasound-based systems. A skin treatment system according to the invention may also comprise both a supply system for a substance and an energy supply system.

When the skin treatment system comprises an energy supply system, the treatment of the skin and the measurement of the sebum and water levels may be coupled. For example, in the case of a hyperactive sebaceous gland in the skin detected by measuring a relatively high sebum level, a laser energy source of the skin treatment system may be set to a high-power laser pulsing mode at 1720 nm for the selective photothermo lysis of the detected sebaceous gland. For more details of such a laser treatment, see for example Sakamoto, Apostolos, Doukas et al., "Selective photothermolysis to target sebaceous glands: theoretical estimation of parameters and preliminary results using a free electron laser", Lasers in surgery and medicine 44, no. 2 (2012): 175-183.

In specific embodiments, the energy source is not the light source configured and arranged to emit said light beam. Hence, in addition to the light source for the optical system, a (further) source of energy may be provided. For instance, the energy source may be a light source (i.e. an additional source, in addition to the light source configured and arranged to emit said light beam (that is used for detection)). However, the energy source may also be an IR source or an RF source (see also above) or an ultrasound source, as, as indicated above, examples of the energy to be supplied for skin treatment may include radio- frequency (RF) energy, ultrasound energy and light energy. The measurement system may be comprised in other types of skin treatment devices. For example, to treat excessive sebum or oily skin conditions, the skin treatment system may have a brush head, wherein for example a frequency of cleansing by means of the brush head may be increased when detecting a high sebum level.

When laser energy is used for skin treatment, a single laser source with different power settings may be used for both the measurement system and the skin treatment system.

The measurement system 1 10 may also be used as a data collection system to monitor skin conditions over a period of time before, during or after skin treatment.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer or processor. In the system claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. A measurement system (1 10) for simultaneous light-based measurement of sebum and water levels in skin (160), the measurement system (1 10) comprising:

an optical system (130) having a light source (120) configured and arranged to emit a light beam (140) having a source wavelength range;

the optical system (130) being configured and arranged to direct the light beam (140) towards the skin (160);

the measurement system further configured and arranged to detect a first light intensity within a first detection wavelength range of light reflected (145) from the skin, configured and arranged to detect a second light intensity within a second detection wavelength range of light reflected (145), and configured and arranged to detect a third light intensity within a third detection wavelength range of light reflected (145) from the skin;

wherein:

the measurement system (1 10) further comprising:

2. The measurement system (1 10) for simultaneous light-based measurement of sebum and water levels in skin (160) according to claim 1,

the measurement system further comprising:

a first detector (150) configured and arranged to detect a first light intensity within a first detection wavelength range of light reflected (145) from the skin;

a second detector (250) configured and arranged to detect a second light intensity within a second detection wavelength range of light reflected (145) from the skin;

a third detector (350) configured and arranged to detect a third light intensity within a third detection wavelength range of light reflected (145) from the skin;

the measurement system (1 10) further comprising:

a processor, coupled to the first detector (150), the second detector (250) and the third detector (350), configured and arranged to determine said first parameter associated with a sebum level and said second parameter associated with a water level of the skin based on the first light intensity, the second light intensity and the third light intensity.

3. The measurement system (1 10) according to any one of the preceding claims, wherein the first detection wavelength range is selected from the group consisting of 1720 nm ± 5 nm, 2305 nm ± 5 nm, 1205 nm ± 5 nm and 910 nm ± 5 nm.

4. The measurement system (1 10) according to any one of the preceding claims, wherein the second detection wavelength range is selected from the group consisting of 1705 nm ± 5 nm, 1733 nm ± 5 nm, 2277 nm ± 5 nm, 2355 nm ± 5 nm, 1 192 nm ± 5 nm, 1218 nm ± 5 nm, 900 nm ± 5 nm and 930 nm ± 5 nm.

5. The measurement system (1 10) according to any one of the preceding claims, wherein the third detection wavelength range is selected from the group consisting of 1695 nm ± 5 nm, 1770 nm ± 5 nm, 2255 nm ± 5 nm, 2375 nm ± 5 nm, 1 182 nm ± 5 nm, 1221 nm ± 5 nm, 886 nm ± 5 nm and 936 nm ± 5 nm.

6. The measurement system (1 10) according to any one of the preceding claims, wherein:

the first detection wavelength range is 1720 nm ± 5 nm;

the second detection wavelength range is 1705 nm ± 5 nm or 1733 nm ± 5 nm; and

the third detection wavelength range is 1695 nm ± 5 nm or 1770 nm ± 5 nm.

7. The measurement system (1 10) according to any one of the claims 1 to 5, wherein:

the first detection wavelength range is 2305 nm ± 5 nm;

the second detection wavelength range is 2277 nm ± 5 nm or 2355 nm ± 5 nm; and

the third detection wavelength range is 2255 nm ± 5 nm or 2385 nm ± 5 nm.

8. The measurement system (1 10) according to any one of the claims 1 to 5, wherein:

the first detection wavelength range is 910 nm ± 5 nm;

the second detection wavelength range is 900 nm ± 5 nm or 930 nm ± 5 nm; and

the third detection wavelength range is 886 nm ± 5 nm or 936 nm ± 5 nm.

9. The measurement system (1 10) according to any one of the preceding claims, the measurement system being further configured and arranged:

- to polarize light within the source wavelength range, thereby generating a polarized light beam; and

to direct the polarized light beam (140) towards the skin (160), the polarized light beam having a first polarization direction;

the measurement system further comprising at least one light filter disposed in a light path of light reflected from the skin (145) to at least one of the first, second and third detectors (150, 250, 350), the light filter being configured to preferentially transmit light having a second polarization direction, wherein the first and second polarization directions are different.

10. The measurement system (1 10) according to claim 9, wherein the first and second polarization directions differ by approximately 90 degrees.

1 1. The measurement system (1 10) according to any one of the preceding claims, wherein a central wavelength of the source wavelength range is in a range from visible light to infrared light.

12. A skin treatment system for supplying a substance for increasing a sebum level and/or a water level of skin, wherein:

the skin treatment system comprises the measurement system (1 10) according to any one of the preceding claims; and

the skin treatment system is configured and arranged to modify at least one characteristic of the substance to be supplied to the skin based on the first parameter and/or the second parameters.

13. A skin treatment system for treatment of skin by means of energy, comprising an energy source and a supply system for supplying energy generated by the energy source to the skin, wherein:

the skin treatment system comprises the measurement system (1 10) according to any one of the claims 1 to 1 1 ; and

the skin treatment system is configured and arranged to modify at least one characteristic of the energy to be supplied to the skin based on the first parameter and/or the second parameter.

14. The skin treatment system according to claim 13, wherein the energy source is not the light source (120) configured and arranged to emit said light beam (140).