GB2541637A - Skin Cream - Google Patents

Abstract

A range of skin creams, wherein each skin cream in the range has a different viscosity due to different percentage water content, and wherein the creams are arranged to be effective for support of the skin's natural barrier function, in different clinical skin types.

Description

SKIN CREAM

Technical Field

This invention relates to a range of skin creams. In particular it relates to a range of skin creams that includes a range of viscosities of skin creams targeted to different skin types. It also relates to methods of providing a suitable skin cream from the range for an individual’s skin type.

Background

The cosmetic appearance of our skin is directly related to its underlying health. Many factors contribute to our overall skin health, but maintaining an intact skin barrier is arguably the most important. The skin's barrier function can be significantly improved by the application of moisturisers, and its cosmetic appearance enhanced. However, a careful selection of any moisturiser is essential, and some understanding of how it works is desirable. To achieve effective hydration, moisturisers need to be 'lipid based emollients', and have the correct physical properties that match your skin type, in terms of its hydration.

Our skin is the barrier between the outside world and the controlled environment inside our bodies. Skin needs to be impermeable, strong and yet supple enough to accommodate movement. It is the largest organ in the body and essential to our overall health. It is part of 'the integument' that contains our hair follicles, sweat and sebaceous glands and our nails. The notion that our outer surface is actually 'just made of dead cells', is far from true. Even the outermost non-cellular layers remain biochemically active, continuously regulating their own thickness and repair.

Skin comprises two layers, the outer Epidermis and the inner Dermis. Beneath this lies the subcutaneous fat layer, which is known as the Sub-cutis. This is shown diagrammatically in figure 1. The Epidermis ranges from 0.1 mm thick, up to 1 mm or more on the palms of the hands or soles of the feet. It is divided into five sub-layers [ranging from living to non-living cells] and hosts a variety of functions from waterproofing and vitamin D synthesis, to protection from infection and UV radiation. Its main cell type is the Keratinocyte, which produces a tough protein called 'Keratin' that is also found in hair and nails. The Keratinocytes are formed in the deepest layer and become flattened and desiccated as they rise through the layers, to form the outer protective layer.

The outer two layers of the Epidermis are known as the Stratum Corneum [SC], These layers consist of tough, non-living cells and are an important component of the skin barrier. Its function is quite simply to keep the external environment out, and our internal tissues in. Effective barrier function is required to remain optimally hydrated, and loss of its function leads to skin dryness, with a dull, rough and scaly outer surface, instead of a soft, smooth and even surface. The SC has a significant impact on our skin's health, and our overall cosmetic appearance, and hence determines our complexion.

Hydration of the skin is grossly mis-understood. The whole concept of external hydration is erroneous. Our skin is water-proof, so that concept of applying water to the skin by applying skin care products is flawed. In fact, the application of water to our skin, especially in the presence of any detergent, dries us out even more.

The human body has a very sophisticated set of mechanisms for regulation of its hydration status, especially with regard to the blood. Simplistically put, we intake water through ingestion, and output waste water through excretion, but the control of this is very carefully balanced. Water that we drink, therefore finds its way through our systems into the capillaries that traverse all of our bodily tissues. Here water is exuded into the tissue spaces and can travel into the surrounding cells for their hydration.

Blends of occlusive emollients, coupled with humectant moisturisers, are essential products in skin care. They are like applying a protective dressing to the skin, to prevent excessive evaporation and provide a temporary restorative cover. This allows the lipid layers to re-form and the cells to regain their volume and shape. In doing so, the gaps between the cells are minimised, and the skin's natural barrier integrity is reestablished. This is shown diagrammatically in figure 5.

The water required to hydrate our skin cells comes from drinking. With regard to hydration, the use of skin care products is essentially to limit excess water loss, and to allow the cells to replenish themselves with water from their deeper tissues.

Skin-type varies widely between individuals and even on different parts of the same person’s body. Because having optimum hydration has such a profound effect on the condition, health and appearance of the skin it is important to use a skin cream that suits the type of skin that it will be applied to. It would therefore be advantageous to have a range of different skin creams that are adapted to different skin types so that the consumer or clinician can choose the most suitable cream for a particular person or area of the body.

The present inventors have appreciated that there is no standardised way of relating a scale of viscosities for skincare product to the range of clinical skin types.

The present inventors have further appreciated that it would therefore be advantageous to have a range of different skin creams that are adapted to different clinical skin types so that the consumer or clinician can choose the most suitable cream for a particular person or area of the body.

With no standardised scale of viscosity relative to intended use for clinical skin type, no quantified advice can he given regarding product selection.

Summary

According to a first aspect of the invention we provide a range of skin creams, wherein each skin cream in the range has a different viscosity due to a different percentage water content.

The formulation of each cream may have a specific relative percentage of water and lipids.

Skin care products (in particular moisturisers) of different viscosities may be provided, to provide effective support of the skin's natural barrier function, in different clinical skin types. The viscosities of the products may be a result of, amongst other things, the ratio of 'lipid to water' in the blend, and the types of lipid used in the (base) formulation.

Table 1 - Suitable viscosities for various skin creams

Table 1 shows the viscosities of skin creams targeted specifically for oily, normal, dry and extra dry skin. cPs is the physical unit of viscosity centipoise. For each skin type a day cream for younger skin and a night cream for younger skin and a day cream for mature skin and a night cream for mature skin are shown.

The viscosities shown in table 1 may vary by up to plus or minus 10 % for each cream.

The range of skin creams may comprise at least four, at least six, at least eight, at least ten, at least twelve, at least fourteen, at least sixteen or at least eighteen creams each having a different viscosity.

The range may comprise creams formulated for at least three, at least four at least five, at least six clinical skin types.

The range may comprise creams formulated for the clinical skin types oily, normal, dry and extra dry skin.

The range may comprise a day cream and a night cream for each skin type.

The night cream for each skin type may have a higher viscosity than the day cream for the same skin type.

The range may comprise a cream for each skin type formulated for mature skin and a cream for each skin type formulated for younger skin. Products formulated specifically for mature skin may be specifically formulated for people who are over 40 years old. Products specifically formulated for younger skin may be specifically formulated for people who are 40 years old or younger.

The cream for mature skin may have a higher viscosity than the cream for younger skin of the same skin type.

The range may comprise sixteen creams: four day creams for younger skin formulated for oily, normal, dry or extra dry skin; four night creams for younger skin formulated for oily, normal, dry or extra dry skin; four day creams for mature skin formulated for oily, normal, dry or extra dry skin; and four night creams for mature skin formulated for oily, normal, dry or extra dry skin.

The skin cream ranges are advantageous because they provide a suitable range of creams that the clinician or consumer can choose from to suit each skin type, age and time of use.

In another aspect the present invention provides a standardised scale of recommended viscosity for skin care products, relative to the clinical skin type for their intended use.

The standardised scale is advantageous because it provides a measure to quickly test the viscosity of potential treatments to check suitability for use on a given clinical skin type. This avoids making subjective judgements and reduces the cost of treatment by avoiding the use of inappropriate treatments. The standardised scale may be based on the values shown in Table 1. Each cream may have a viscosity in the range of plus or minus ten percent of the value shown in table 1.

Skin cream may comprise water and a base composition. The base composition may comprise a combination of humectants to draw water into the skin and hydrate it and emollients to prevent water from being lost from the skin through evaporation, drying the skin out.

The base composition may comprise one or more different humectants and one or more different emollients and the percentage of humectants and emollients in the base composition may be varied.

The drier the skin the lower percentage of water is required and the higher percentage of base composition is required. The oilier the skin the higher percentage of water is required and the lower percentage of base is required. Figure 6 shows how the viscosity of cream increases as the percentage of water decreases.

The range may comprise at least one cream adapted for oily skin, at least one cream adapted for combination skin, at least one cream adapted for normal skin, at least one cream adapted for dry skin, and at least one cream adapted for extra dry skin. The range may further comprise at least one cream adapted for irritated skin and/or one cream adapted for sensitive skin.

The range may comprise a face cream, an eye area cream, a body cream, a hand cream, a foot cream, a cream for the scalp.

The creams in the range may be adapted to preserve the appearance of ageing skin, for example skin of people over the age of 40. The creams in the range may be adapted to prevent ageing, for example of skin of people 40 years old and younger. Creams adapted to preserve the appearance of ageing skin may have a lower water content and/or higher viscosity than creams adapted to prevent ageing. This is advantageous because skin generally becomes drier as it ages and therefore, ageing skin requires a lower water content compared to younger skin.

The creams in a range may be adapted as day creams or as night creams.

The creams in the range may be hypoallergenic.

The creams may comprise colour adapted to the colour of the skin, for example the skin creams may comprise a range of skin colours to provide a range of tinted moisturisers adapted for different skin tones. The range of skin creams may comprise a cream with green tint to mask redness of the skin.

The term cream is used herein to deseribe eaeh of the products in a range. Each cream comprises comprise water and a base composition. The base composition may comprise at least one humectant and at least one emollient. The percentage of water in each cream in the range may be different. The percentages and types of humectants and emollients in the base composition of each cream may be the same throughout the range while the percentage of water to base composition is changed for each cream in the range The percentages and types of humectants and emollients in the base composition may be different for one or more creams in the range and the water content of each of the creams in the range may be different.

The term cream is used herein for all of the products in the range whatever the water content however, creams as described herein with a high water content may also be known as lotions. Creams in the present range of creams that have a lower water content may also be known as ointments.

Each cream in the range may comprise one or more emulsifiers to allow the base composition to combine with the water to form an emulsion. Each cream in the range may comprise one or more stabilisers to keep the emulsion stable and prevent the base composition and the water from separating from each other.

The cream may further comprise one or more further active ingredients such as vitamins, antioxidants, sunscreen, UVA filers, UVB filters.

The cream may further comprise one or more further inactive ingredients such as colours or perfumes.

According to a further aspect of the invention we provide a method for making a range of creams comprising the steps of: a) formulating a base composition comprising one or more humectants and one or more emollients; b) combining portions of the base composition with different amounts of water to provide a range of creams, each with a different percentage of water.

There now follows by way of example only a detailed description of the present invention with reference to the accompanying drawings, in which;

Figure 1 shows a cross-sectional view of the full thickness of human skin;

Figure 2 shows a cross-sectional view of the epidermis of human skin highlighting the five layers of the epidermis;

Figure 3 shows a cross-sectional view of cells in the epidermis in healthy skin, the cells of the skin barrier are optimally hydrated and fit together with few gaps between them producing a smooth and even skin surface. ;

Figure 4 shows a cross-sectional view of the epidermis in skin that has a breakdown of the skin barrier, which leads to, the skin becoming dehydrated and prone to irritation, with a loss of its tone and smooth complexion;

Figure 5 shows a view of the epidermis after application of emollient cream, gaps between the cells are minimised, and the skin's natural barrier integrity is re-established;

Figure 6 shows a graph of the mean viscosity, aqua and base contents of creams for different types of skin. The amount of water in the creams is shown as a line with triangles, the amount of base in the creams is shown by a line with circles and the viscosities of the creams is shown as a solid line with no markers; and

Figure 7 shows the viscosities of both day and night creams formulated according to the present invention for oily, normal, dry and extra dry skin.

Detailed description

Skin comprises two layers, the outer Epidermis and the inner Dermis. Beneath this lies the subcutaneous fat layer, which is known as the Sub-cutis. This is shown diagrammatically in figure 1. The Epidermis ranges from 0.1 mm thick, up to 1 mm or more on the palms of the hands or soles of the feet. It is divided into five sub-layers [ranging from living to non-living cells] and hosts a variety of functions from waterproofing and vitamin D synthesis, to protection from infection and UV radiation. Its main cell type is the Keratinocyte, which produces a tough protein called 'Keratin' that is also found in hair and nails. The Keratinocytes are formed in the deepest layer and become flattened and desiccated as they rise through the layers, to form the outer protective layer — the Stratum Corneum.

The five layers of the Epidermis and their transitions are shown diagrammatically in figure 2, with the two outer most layers forming the Stratum Corneum.

The Dermis is much thicker than the epidermis, ranging from between 1mm on the eyelid to 5mm on the back. It forms a matrix of living cells that supports other structures such as hair follicles, pain and sensory nerves, along with sebaceous and sweat glands. This layer contains specialised supporting tissues in the form of collagen and elastin fibres that give the skin its strength and elasticity.

In addition, our skin has important metabolic functions; such as the synthesis of Vitamin D, and immunological functions, known as immune surveillance.

Beneath the skin is the subcutaneous fat layer, or Sub-cutis, which contains the blood vessels, free nerve endings and complex sensory receptors. This layer is important for thermo-regulation, with increased or decreased amounts of blood flow causing heat loss or conservation. Our subcutaneous fat is also important in padding and protecting our skin over pressure areas and bony prominences.

The skin barrier

The outer two layers of the Epidermis are known as the Stratum Corneum [SC]. These layers consist of tough, non-living cells and are an important component of the skin barrier. Its function is quite simply to keep the external environment out, and our internal tissues in. Effective barrier function is required to remain optimally hydrated, and loss of its function leads to skin dryness, with a dull, rough and scaly outer surface, instead of a soft, smooth and even surface. The SC has a significant impact on our skin's health, and our overall cosmetic appearance, and hence determines our complexion.

Microscopic examination of the SC has led to its description of being like a 'brick wall', as it appears to have a similar construction. The cells are square shaped, fairly rigid and laid out evenly in rows, like bricks. There is a matrix of lipids that bind all the cells together, akin to mortar. The lipids are laid out in sheets, and are able to slide against each other, giving a degree of flexibility. Larger lipids form keystonelike anchors, giving strength to the overall structure.

However, unlike a wall, the situation in our living, moving and ageing skin is in constant state of change as we perpetually adapt to new situations or environments. The skin barrier needs to be flexible and adaptable to these new surroundings, as an effective skin barrier is dependent on its total architecture remaining intact. Furthermore, an intact and functioning skin barrier needs to be capable of selfregulation and repair.

The skin cells [keratinocytes] contain substances called 'natural moisturising factors' [NMF's] which strongly attract water from the surrounding tissue fluid into them. This causes them to swell and plump up against their neighbours, filling any spaces between them. This water comes from the lower epidermal and dermal layers, which are constantly replenished by their capillary circulation. Any remaining gaps are plugged by our own naturally occurring lipids, such as sebum, and thus water loss is carefully controlled. In healthy skin, the cells of the skin barrier are therefore optimally hydrated, with few gaps between them producing a smooth and even skin surface. This is shown diagrammatically in figure 3.

Loss of skin barrier function A breakdown of the skin's barrier leads to excessive trans-epidermal water loss [TEWL], and the opportunity for external irritants to gain entry and cause problems. This can be part of the natural ageing process, or brought about by over-washing and other damaging activity. The natural ageing process includes a loss of elasticity and a decrease in skin water content.

The water content of skin is in the range of 10 to 30 per cent, and decreases with age. Production of sebum, skin’s own natural lipid, also reduces with age creating further stress to the skin barrier function and integrity. Photo-ageing through UV light exposure is known to irreversibly damage elastin and collagen fibres, and leads to premature wrinkling of the skin.

Loss of lipids from the matrix is associated with a reduction in the hydrostatic pressure within the cells, and a loss of their shape and volume. This leads to the opening up of tiny channels between the cells. Skin barrier breakdown therefore leads to, the skin becoming dehydrated and prone to irritation, with a loss of its tone and smooth complexion. This is shown diagrammatically in figure 4. Loss of skin barrier function is also seen in medical conditions, such as eczema and psoriasis.

Moisturisers versus emollients

The terms moisturiser and emollient are often used interchangeably. This is incorrect as they each have specific functions and meanings. A moisturiser is a topical application whose function is to actively hydrate the skin by attracting and drawing water into its cells. To this end, these products contain humectants within their formulation. Humectants are important molecules such as urea and glycerine, that help draw water into the skin. This water comes from tissue fluid contained in the deeper layers of the skin.

Emollients are occlusive products, that, when applied to the skin, fill the small channels within the SC and prevent water loss through excessive TEWL. They also make the skin feel smoother by filling in surface inconsistencies. They are lipid containing products, and can have a range of physical characteristics including smoothness, wetness or greasiness. The ideal emollient should mimic the effect of our natural skin epidermal lipids as closely as possible.

Skin hydration and associated products

Hydration of the skin is grossly mis-understood. The whole concept of external hydration is erroneous. Our skin is water-proof, so that concept of applying water to the skin by applying skin care products is flawed. In fact, the application of water to our skin, especially in the presence of any detergent, dries us out even more.

The human body has a very sophisticated set of mechanisms for regulation of its hydration status, especially with regard to the blood. Simplistically put, we intake water through ingestion, and output waste water through excretion, but the control of this is very carefully balanced. Water that we drink, therefore finds its way through our systems into the capillaries that traverse all of our bodily tissues. Here water is exuded into the tissue spaces and can travel into the surrounding cells for their hydration.

Blends of occlusive emollients, coupled with humectant moisturisers, are essential products in skin care. They are like applying a protective dressing to the skin, to prevent excessive evaporation and provide a temporary restorative cover. This allows the lipid layers to re-form and the cells to regain their volume and shape. In doing so, the gaps between the cells are minimised, and the skin's natural barrier integrity is reestablished. This is shown diagrammatically in figure 5.

The water required to hydrate our skin cells comes from drinking. With regard to hydration, the use of skin care products is essentially to limit excess water loss, and to allow the cells to replenish themselves with water from their deeper tissues.

Clinical skin types

It is important to classify skin types in a number of ways, in order to aid diagnosis and prescribe appropriate treatments. The Fitzpatrick classification grades our genetically determined sun sensitivity and tanning ability, and is split into six prototypes. We also classify skin by how it feels to examination in clinical practice, and most people fall into four main groups; Oily, Normal, Dry and X-Dry.

The determining features regarding our hydration level is complex and includes; genetic traits and environmental factors, such as humidity and the use of washing agents. Additionally, it is well documented that our skin type tends to change as we age; moving towards the drier end of the spectrum over time. Different clinical skin types therefore require a range of different products from being 'lipid light' to being more 'lipid heavy' at the other, where skin barrier breakdown may be more pronounced.

Skincare products

To have an understanding of skin products, we must address their base formulations. This is fundamental to how they work with regard to supporting skin barrier function, and acting as the 'delivery system' for any active elements added. Purified water, is the main solvent used, into whieh, other ingredients are added. 'Lipid' is a general term that encompasses oils, fats and waxes.

Oil and water do not readily mix, so an emulsifier is required to blend these together. A stabiliser is then required for the products to remain mixed. The choice of lipids selected, and their relative amounts, determines the physical characteristics of the final emulsion. There are many other factors which affect the consistency of the base formulation, including; the ambient temperature, other constituents added, and method of manufacture.

The important beneficial components added to the base formulation of a skin care product are known as 'active ingredients'. These constitute a smaller proportion of the formulation, but confer additional benefits for the skin. The 'actives' ingredients are carried into the deeper layers, and can influence the environment and working of the living cells. The selection of these active ingredients is a key part of the design process for any product. They should be tailored to the specification of the product, and each active should have been scientifically tested and shown to provide benefit.

Ointments, creams and lotions

Ointments, creams and lotions are different emulsions of lipids in water; the significant difference being, the type of lipid used, and the ratio of 'lipid to water' mixed. Lotions are the lightest product, with very high water content and only a small amount of'light' lipids emulsified into their base formulation.

Products for Oily skin are more 'lotion-like', as shown by their higher water content. Then, they become more like creams for the products designed for the Normal and Dry clinical skin types. For products suited for X-dry skin, they need to be more “ointment-like”. A range of products designed to cater for the range of clinical skin types, therefore should show the trends of: 1. An increase in the lipid content of its base formulation, as products traverse the spectrum of clinical skin types. 2. A decrease in the water content of its base formulation as products traverse the spectrum of clinical skin types. 3. An increase in viscosity as the products traverse the spectrum of clinical skin types.

Viscosity

In Figure 6, the line without markers represents the products viscosity, or thickness. This increases significantly as we move across the clinical skin types that these products are designed for. The viscosity of a product, be it a lotion, cream or ointment, is a function of its lipid and water constituents. A water based lotion is of low viscosity, a thick ointment is a very high viscosity and creams span the gap in between.

Viscosity is a very important aspect in the skincare products of the present invention, as it reflects how the products are prescribed by Dermatologists in clinical practice.

Many different test samples were created and their clinical performance assessed, before making the final selections. The viscosity of these noticeably increases as we transition for Oily to X-Dry. The night products are all purposely thicker than the day versions. Furthermore, as the more mature skin requires increased skin barrier support, the products formulated for mature skin' are designed to be more viscous than the products formulated for younger skin.

Skin ageing and moisturisers

The process of skin ageing is complex, and has several components, two if which include; chronological ageing and photo-ageing. The natural ageing process of skin includes a loss of elasticity and a decrease in its overall water content. The water content of our skin sits in the range of 10 to 30 per cent, and decreases as we age. Production of sebum, the skin’s own natural lipid, also reduces. Lipid based emollients in this instance, act as replenishment therapy, and as we age, the more viscous the products we require.

Photo-ageing, and sun-damage, is due to exposure to ultra-violet radiation in sunlight. This is known to irreversibly damage our elastin and collagen fibres, and lead to premature wrinkling of the skin. Sun protection ingredients, when added to moisturisers, are proven to reduce the long-term damage done by exposure to UV radiation. It is known that the regular use of skin care products that contain sun protective ingredients can decrease the incidence of UV related skin cancers, when applied correctly.

Results of Viscosity Tests

Two skin cream ranges were prepared, one designed for the mature skin and the other for younger skin. Each range had variants for the clinical skin types of oily, normal, dry and extra dry (X-dry), and each of these has a variant for day and night use. This created 16 different creams, all with different performance characteristics, [for age, time of use and skin type] all with different viscosities.

The formulations were adjusted and refined through heuristic assessment until judged ideal for each of the requirements, based upon an extensive experience of patients traversing all clinical skin types. A clinical assessment was then made testing each cream on a skin type specified for its intended use, including younger and older test subjects, with consideration given for day or night use.

At that stage, the viscosity of each variant was measured. Measurements were carried out using a Brookfield Viscosimeter, with Helipath accessory and T-bar spindles. This arrangement permits viscosity/consistency measurements in relative centipoise values for pastes or creams having limited flow characteristics.

The results of the viscosity tests are shown in Figure 6. As can be seen in figure 6 when the amount of water in the cream (line with triangles) decreased the viscosity of the cream (solid line without markers) increased. The increased viscosity creams provide more suitable creams for dry skin to prevent water loss from the skin and allow the water-balance in the skin to be restored. Surprisingly adding less water to the creams made them more hydrating to the skin because they prevented water loss from the skin. The higher water content creams, formulated for oily skin have a lower viscosity and are suitable for oily skin, which does not require additional oil from a cream, the high water content is drying to the skin and therefore balances the natural oiliness of oily skin.

From the experiments performed a standardised scale was devised, of recommended viscosity for skin care products, relative to the clinical skin type for their intended use.

The standardised scale is advantageous because it provides a measure to quickly test the viscosity of potential treatments to check suitability for use on a given clinical skin type. This avoids making subjective judgements and reduces the cost of treatment by avoiding the use of inappropriate treatments.

The viscosities of each of the day and night creams for each age range and skin type is shown in figure 7.

Consideration of the base formulation of a product is essential to how it behaves a medical moisturiser and also for the delivery of any active ingredients it may contain.

This should be tailored to its intended use as a moisturiser, taking into consideration, clinical skin type, timing of use and age of the skin.

Conclusion

An intact skin barrier is essential for maintaining optimal skin health. When breakdown of this skin barrier occurs, we are exposed to external irritants resulting in inflammation, redness and itching. Desiccation of the 'Stratum Comeum' skin cells leads to dehydration of the skin and further dryness through 'Trans Epidermal Water Loss'. This results in flaking, cracking and wrinkling of the skin, along with a loss of elasticity and tone. All of these adversely affect our cosmetic appearance.

Emollient therapies are useful to support our Stratum Corneum and its barrier function. However, these must be of the correct composition [of water to lipid] to be functional, and specific for each clinical skin type. This is reflected by its viscosity, and a range of viscosities is required to cover variations in skin type, age and day or night usage.

Supporting our skin's natural barrier function with lipid based emollients, is one of the most important things we can do to improve and maintain our skin's youthful Cosmetic appearance.

Advantageously, the above described range of skin creams having respective viscosities which are tailored for particular skin types avoids the risks involved in making subjective judgements. The provision of such a range also reduces cost by avoiding the use of inappropriate treatments.

Claims (13)

1. A range of skin creams, wherein each skin cream in the range has a different viscosity due to different percentage water content, and wherein the creams are arranged to be effective for support of the skin’s natural barrier function, in different clinical skin types.

2. The range of skin creams according to claim 1 wherein the range comprises at sixteen creams each having a different viscosity.

3. The range of skin creams according to claim 1 or claim 2 wherein the range comprises creams formulated for four clinical skin types.

4. The range of skin creams according to any one of the preceding claims wherein the range comprises creams formulated for clinical skin types oily, normal, dry and extra dry skin.

5. The range of skin creams according to any one of the preceding claims wherein the range comprises a day cream and a night cream for each clinical skin type.

6. The range of skin creams according to any one of the preceding claims wherein the night cream for each clinical skin type has a higher viscosity than the day cream for the same clinical skin type.

7. The range of skin creams according to any one of the preceding claims wherein the range comprises a cream for each clinical skin type formulated for mature skin and a cream for each clinical skin type formulated for younger skin.

8. The range of skin creams according to any one of the preceding claims wherein the creams for mature skin may have a higher viscosity than the creams for younger skin of the same clinical skin type.

9. The range of skin creams according to any one of the preceding claims wherein the range comprises 16 creams: four day creams for younger skin formulated for oily, normal, dry or extra dry skin; four night creams for younger skin formulated for oily, normal, dry or extra dry skin; four day creams for mature skin formulated for oily, normal, dry or extra dry skin; and four night creams for mature skin formulated for oily, normal, dry or extra dry skin.

10. The range of skin creams according to any one of the preceding claims wherein the range comprises 16 creams having viscosities within the range +/- 10 % of the viscosities shown in table 1.

11. A standardised scale of recommended viscosity for skin care products, relative to the clinical skin type for their intended use.

12. A range of skin creams as described herein with reference to the examples and figures.

13. A standardised scale as described herein with reference to the examples and figures.