MXPA97006398A - Composition for the treatment of the p - Google Patents

Abstract

The present invention relates to an oil in water emulsion for treating the skin, comprising from about 2 to about 10 weight percent of a cationic emulsifier such as the dimethyl distearyl ammonium halide, a substantially non-ionizable humectant such as glycerin and a low acid material having a dissociation constant of about 1 to 6. The amount of the low acid material is such that the pH of the finished emulsion is about 2.5 to 4.5. A method for preparation of the emulsion is also described

Description

COMPOSITION FOR THE TREATMENT OF SKIN BACKGROUND OF THE INVENTION This invention relates to improved cosmetic emulsions, especially to emulsions useful for moistening and conditioning the skin. This invention relates more particularly to cosmetic compositions using cationic emulsifiers, especially cosmetically acceptable skin lotions or creams having an emulsified petrolatum base or mineral oil base. In various embodiments, this invention also relates to methods for preparing skin treatment compositions emulsified by cationic surfactants and having a petrolatum or mineral oil base. A normal corneal layer of epidermis usually contains 10-20% moisture, which helps to impart elasticity, flexibility, or softness to the skin and to maintain a protective effect for the skin. When the moisture content decreases to less than 10% due to changes in environmental or similar conditions, the skin loses its elasticity and protective function and develops a so-called dry skin condition that causes several skin problems. A wide variety of emulsions have been used to moisten the skin. Both oil-in-water (water-out) emulsions and water-in-oil emulsions (oil out) have been tested. The emulsifiers employed in these formulations have included anionic, nonionic, cationic emulsifiers and mixtures thereof, although the most common commercial products have used anionic and nonionic emulsifiers. A skin cream based on cationic emulsifiers, which has been popular with consumers, is the CUREL lotion sold by Bausch & Lomb Incorporated. The product is a skin treatment composition that uses a quaternary ammonium compound as the sole emulsifying agent in an oil-in-water emulsion. By using particular quaternary ammonium compounds, superior properties are obtained for a hand treatment product. Cosmetically acceptable products, including a substantial amount of petrolatum or mineral oil, can be prepared in combination with fatty alcohols and fatty ester emollients. The composition has excellent tactile properties and, at the same time, provides good protection for the user's hands. See United States Patent No. 4,389,418. Other skin treatment products using cationic surfactants are described in U.S. Patent Nos. 4,781,918, 5,013,763 and 5,135,748. Hydroxy (alpha and beta), keto, carboxylic and dicarboxylic acids have long been used in a wide variety of cosmetic products in detail to remove dead cells from the surface of the skin and to assist in humidification, thus providing a clearer and more beautiful complexion. See U.S. Patents Nos. 3,879,537, 3,920,835, 3,984,566, 4,105,783, 4,197,316, 4,234,599, 4,380,549, and 5,691,171. See also Smith, W.P., "Hydroxy Acids and Skin Aging", Cosmetics & Toiletries, Vol. 109, pages 41-48 (September, 1994). They are components of interest in current cosmetic products due to the demand for products that diminish the appearance of fine lines on the face and improve the appearance of escapes or dry skin. Treatments for dry skin often involve the application of hydrocarbons such as petrolatum or mineral oil to cover the skin with a hydrophobic occlusive film that prevents the loss of water from the surface of the skin into the environment. Other components such as the hydroxy acids mentioned above and hydrophilic humectants such as polyols, especially glycerin, are included in formulations to add moisture to the skin. It would be desirable to provide more effective formulations that not only prevent water loss from the skin, but also act more efficiently to directly hydrate dry skin.

COMPENDIUM OF THE INVENTION A skin treatment product has now been discovered that exhibits superior humidification properties. The product is an oil-water emulsion for topical application comprising from about 2 to about 10% by weight of a particular cationic emulsifier, from about 1 to about 40% by weight of a water-soluble humectant, substantially non-ionizable, and a weakly acidic, pharmaceutically acceptable material in an amount sufficient to adjust the pH of the finished emulsion to a value in the range of about 2.5 to about 4.5, preferably 3.0 to 4.0, when the emulsion is diluted with purified water up to 10 times its weight. The cationic emulsifier employed in this invention is a quaternary ammonium compound of the formula R2 I where Rx and R2 are each long chain, substantially linear alkyl groups having from about 16 to about 22 carbon atoms, R3 and R4 are each lower alkyl groups having from about 1 to about 3 carbon atoms and X is a salt-forming anion. The humectant is best exemplified by glycerin. The weakly acid component has a dissociation constant (pKa) in the range of about 1 to about 6. The selection of the weakly acid component is not considered strictly critical, although alpha hydroxy acids, especially alpha hydroxy acids of the formula are currently preferred.

OH I R5-C-COOH I wherein R5 and R6 are aliphatic hydrocarbon groups and ester having from 1 to 10 carbon atoms. Preferred alpha-hydroxy acids are selected from the group consisting of citric acid, glycolic acid, glucuronic acid, galacturonic acid, alpha hydroxybutyric acid, alpha hydroxyisobutyric acid, lactic acid, malic acid, mandelic acid, mucic acid, pyruvic acid, alpha-phenylactic acid , alpha phenylpyruvic acid, saccharic acid, tartaric acid, and tartronic acid. Glycolic acid, lactic acid, tartaric acid and malic acid are particularly preferred. Although the mechanism by which the emulsion of this invention moistens the skin is not fully understood, it is currently thought that the unusual effectiveness of the composition is related to the pH and temperature-dependent ionization properties of the system. More particularly, it is believed that the temperature change accompanying the application of the product to the skin induces a phase change that causes the water-soluble, substantially non-ionizable humectant (eg, glycerin) to move from the micellular interface ( where it is associated with the hydrophilic portion of the cationic emulsifier) to the outer surface of the emulsion (ie, to the air / emulsion and skin / emulsion interfaces). The temperature change additionally ionizes the weakly acidic component, displacing the humectant component associated with the cationic emulsifier at the micellular interface. The result is a formulation that has the ability to deliver humectant (eg, glycerin) to the stratum corneum in amounts beyond those foreseeable from the simple consideration of the humectant concentration. Components can be added, in addition to those indicated above, in the formulation, as will be apparent to those skilled in the art. Examples described in more detail below include petrolatum or mineral oil components, fatty alcohol components, fatty ester emollient components, lubricants such as silicone oils, and preservatives. Being an oil-in-water emulsion, the formulation also includes a significant portion of purified water. A related, but distinct aspect of the invention relates to the stability of the emulsion. More specifically, it has been found that particularly desirable compositions are obtained if the formulation is prepared in the substantial absence of added salt.

A further aspect other than the invention relates to methods for preparing oil-in-water emulsions of the type exemplified by the formulation of this invention, ie, formulations containing water-insoluble components, a water-soluble humectant, and an emulsifier. cationic The method includes: (a) providing an aqueous solution of a weakly acidic material having a pKa within the range of about 1 to about 6, said solution having a pH in the range of from about 2 to about 4, preferably from 3 to 3.8 (measured at 25 ° C); (b) forming an aqueous mixture of the water insoluble components and the humectant; (c) adding the cationic emulsifier to the aqueous mixture at a temperature of from about 80 to about 95 ° C, preferably from about 84 to about 88 ° C, to form a water-in-oil emulsion; (d) cooling the emulsion formed in step (c) to a temperature in the range of about 45 to about 60 ° C, preferably about 52 to about 55 ° C, by direct injection of purified water, causing this way a phase inversion and forming an oil-in-water emulsion; and (e) adding said aqueous solution of weakly acidic material at a temperature in the range of about 45 to about 55 ° C to the emulsion formed in step (d) to produce an oil-in-water emulsion having a pH within the range of about 2.5 to about 4.5 when diluted with purified water to 10 times its weight. The method is illustrated and described in more detail in the following description.

DETAILED DESCRIPTION OF THE INVENTION The quaternary ammonium emulsifiers used in this invention have the general formula R2 I [R, -N-R3] + X ~ I R4 where Rx and R2 are each long-chain, substantially linear alkyl groups having from about 16 to about 22 carbon atoms, R3 and R4 are each alkyl groups lower ones having from about 1 to about 3 carbon atoms and X is a salt-forming anion. Preferably, the salt-forming anion is chloride, bromide or iodide. The cationic emulsifiers preferably exhibit hard, waxy, non-tacky characteristics. The most preferred cationic emulsifier is dimethyl distearyl ammonium chloride. The cationic emulsifier is preferably present in the emulsions of this invention in concentrations of about 2 to about 10% by weight, preferably about 3 to 8% by weight. The humectants act as hydroscopic agents, which increase the amount of water retained in the stratum corneum and which contribute to the softening of the surface of the skin. The humectants employed in the formulations of this invention are water soluble and are substantially non-ionizable. By "substantially non-ionizable" it is understood that there is no significant or detectable dissociation in water. Suitable humectants for the formulations of this invention include glycerin, propylene glycol, sorbitol, polyethylene glycol, 1,2,6-hexantriol, hydrolysates of hydrogenated starch, inositol, mannitol, PEG-5 pentaerythritol ether, polyglyceryl sorbitol, xylitol, sucrose, and the like. Glycerin is a particularly preferred humectant. The humectant is preferably present in the emulsions of this invention in concentrations of from about 1 to about 40% by weight, more preferably from about 1 to about 20% by weight, and still more preferably from about 5 to about 15% by weight. The selection of the weakly acid, pharmaceutically acceptable material employed in this invention is not strictly critical, as long as the acid dissociation constant (pKa) is within the range of from about 1 to about 6, preferably from about 2.5 to about 5.0 (measured at 25 ° C). The pKa of the acid component is preferably greater than the pH of the finished emulsion. PKa is an expression of proton dissociation in solution and is a negative record of the dissociation constant. Therefore, an acid is stronger if its pKa number is lower. Some In¬ acidic materials have more than one proton and, therefore, have more than one pKa. An example is citric acid having three protons that have the following acid dissociation constants: pKal = 3.13; pKa2 = 4.76; and pKa3 = 6.40. The selected acid material will have at least one proton within the desired pKa range and preferably each of the protons of the acid material will be within the indicated pKa range. Examples include hydroxymonocarboxylate acids, hydroxydicarboxylic acids, hydroxy-aryl-boxyl acids, and keto acids. The hydroxy polycarboxylic acids may be provided as the alpha or beta analogs and may be present as free acids, peroxides, lactones, amides, esters, or salts. Illustrative of the variety of acids include saccharic acid, 2-hydroxyglutamic acid, 3,4-dihydroxyglutamic acid, 2,5-dihydroxy-6-aminohexanoic acid, acetopyruvic acid, acetyl pyruvic acid, beta-fluoropyric acid, tartaric acid, citric acid, 2-hydroxybenzoic acid (salicylic acid), 2-hydroxy-2-methylbutyric acid, 2-hydroxy isobutyric acid, mandelic acid, and 2-hydroxy caproic acid. A class of preferred acids are hydroxy, dihydroxy, and keto amino acid analogues. Examples include glycolic acid, lactic acid, pyruvic acid, glyceric acid, malic acid, beta phenyl lactic acid, beta phenyl pyruvic acid, alpha hydroxy isovaleric acid, alpha hydroxy isocaproic acid, 2,3-dihydroxybutanoic acid, and 2 acid, 6-dihydroxyhexanoic. Preferred acids are selected from the group consisting of citric acid, glycolic acid, glucuronic acid, galacturonic acid, alpha hydroxybutyric acid, alpha hydroxyisobutyric acid, lactic acid, malic acid, mandelic acid, mucic acid, pyruvic acid, alpha-phenylactic acid, acid phenylpyruvic alpha, saccharic acid, tartaric acid, tartronic acid, and mixtures thereof. Another class of preferred acids are described by the general formula OH i R5 - C - COOH I R < where R5 and R6 are aliphatic hydrocarbon groups and ester having from 1 to 10 carbon atoms. Particularly preferred materials within this class are acids selected from the group consisting of glycolic acid, lactic acid, tartaric acid, malic acid, and mixtures thereof. Even more preferred materials within this class are selected from the group consisting of glycolic acid, lactic acid, and mixtures thereof. It can happen that the concentration of cations such as Ca, Fe, K, Na, P, S, and Si affects the ability of the emulsions of this invention to transport humectants through the skin membrane. Although this phenomenon is not understood, the emulsions of this invention will desirably include the following cations (shown as ppm by weight): Calcium 0.1-14.0 Iron 0.3-3.0 Potassium 0.5-10.0 Sodium 0.5-103.0 Phosphorous 0.9-7.0 Sulfur 0 , 9-70.0 Silicone 0.3-4.0 The amount of acidic material added to the formulation sufficient to adjust the pH of the finished emulsion to a value in the range of about 2.5 to about 4.5, preferably from 3.0 to 4.0, when the emulsion is diluted with purified water up to 10 times its weight. The pH is measured at 25 ° C. In particularly preferred embodiments of this invention, the amount of acidic material in the emulsion is in the range of about 0.5 to 7% by weight, more preferably 4 to 6% by weight. This aspect of the invention will be illustrated in more detail in the examples and in the description of the process for preparing the emulsion. In addition to the cationic surfactant or emulsifier and the alpha-hydroxy acid components, the emulsions of this invention will include other components conventionally used in skin treatment formulations. Such other components include (a) petrolatum or mineral oil, (b) fatty alcohols, (c) fatty ester emollients, (d) silicone oils or fluids, and (e) preservatives. These components must be generally safe for application to human skin and must be compatible with the other components of the formulation. The selection of these components is generally within the skill of the art. The following description refers to particular components, although it will be understood that it is intended that combinations or mixtures are also included. The petrolatum component or mineral oil selected will generally be USP or NF grade. The petrolatum can be white or yellow. The viscosity or degree of consistency of the petrolatum is not strictly critical. The petrolatum can be partially replaced with mixtures of hydrocarbon materials that can be formulated to look like petrolatum in appearance and consistency. For example, mixtures of petrolatum with microcrystalline wax, paraffin wax, and the like can be melted together. Preferred mineral oils are white mineral oils that have a viscosity of 6.7 to 69 centistokes at 40 ° C, a specific gravity (SG 15.6 ° C / 15.6 ° C) of 0.828 to 0.890, and a pour point maximum of -18 to -7 ° C. Even more preferred mineral oils have a viscosity of 6.7 to 17.0 centistokes at 40 ° C, a specific gravity of 0.828 to 0.860, and a maximum pour point of about -7 to -10 ° C. When used, the petrolatum or mineral oil component is included in the formulations at a concentration of from about 1 to about 10% by weight, more preferably from about 2 to about 6% by weight. The fatty alcohols (typically monohydric alcohols) used in the formulations of this invention stabilize the emulsion and provide a cosmetically acceptable viscosity. The selection of the fatty alcohol is not strictly critical, although generally saturated alkanols of C12 to C32, preferably of C14 to C22, will be used substantially. Examples include stearyl alcohol, ketoestearyl alcohol, myristyl alcohol, behenyl alcohol, arachidonic alcohol, isosteryl alcohol, and isocetyl alcohol. Cetyl alcohol is preferred and can be used alone or in combination with other fatty alcohols. When used, the fatty alcohol is preferably included in the formulations of this invention in a concentration in the range of about 1 to about 8% by weight, more preferably about 2 to about 4% by weight. The fatty ester emollients improve the tactile properties of the composition. Examples of suitable fatty esters for use in the formulation of this invention include isopropyl myristate, isopropyl palmitate, isopropyl isostearate, isostearyl isostearate, diisopropyl sebacate, propylene glycol dipelargonate, 2-ethylexyl isononoate, 2-ethylhexyl stearate, C12 fatty alcohol lactate -C16, isopropyl lanolate, 2-ethyl-hexyl salicylate, and mixtures thereof. The currently preferred fatty ester is isopropyl palmitate. When used, the fatty ester emollient is preferably included in the formulations of this invention in a concentration of from about 1 to about 8% by weight, more preferably from about 2 to about 5% by weight. Oils or silicone fluids are used to improve the lubricity of the composition during application to the skin. Preferably the viscosity of the silicone component at a temperature of 25 ° C is from about 5 to about 12,500 centistokes. Examples of suitable materials are dimethyl polysiloxane, diethyl polysiloxane, dimethyl polysiloxane, diphenyl polysiloxane, cyclomethicone, trimethyl polysiloxane, diphenyl polysiloxane, and mixtures thereof. Currently, dimethicone - a dimethylpolysiloxane blocked at the end with trimethyl units - is preferred. Dimethicone having a viscosity between 10 and 1000 centistokes is particularly preferred. When used, silicone oils are preferably included in the formulations of this invention in a concentration of from about 0.1 to about 5% by weight, more preferably from about 1 to about 2% by weight. The formulation may also contain other conventional additives used in cosmetic emulsions. Such additives include aesthetic enhancers, fragrance oils, dyes, preservatives, sunscreen additives, and medications such as menthol and the like. Preferred aesthetic enhancers are polyqua-ternium 31 and aluminum starch octenylsuccinate. Sometimes salts are used to adjust the viscosity of cationic emulsions. However, in a different aspect of this invention, it has been found that the salt in high concentrations tends to destabilize the formulations of the present invention. Some salt will form during the preparation of the emulsion. For example, as described in more detail below, it is sometimes desirable to adjust the pH of the weakly acidic material. However, it is preferred that the formulation be prepared in the substantial absence of added salt. The term "added salt" means that salts formed as a consequence of pH adjustment of other components added to the formulation are excluded. In more preferred embodiments of this invention, the total salt concentration of the composition will not be greater than 0.5 molar and more preferably is within the range of about 0.1 to about 0.2 molar. The water employed in the formulations and method of this invention is purified water obtained, for example, by distilling ordinary tap water, purifying ordinary water through an ion exchange resin, or by other techniques apparent to those skilled in the art. The water preferably represents from 30 to 90% by weight, more preferably from 55 to 85% by weight of the emulsions of this invention. The oil-in-water emulsions of this invention are prepared by first forming an aqueous mixture of the water-insoluble components and the humectant. Water-insoluble components include the cationic emulsifier, the petrolatum or mineral oil component, the fatty alcohol component, the fatty ester emollient, and the silicone oil component. The components are preferably added to the water in the following sequence: humectant, petrolatum / mineral oil, fatty ester, silicone oil, fatty alcohol. After these components have been thoroughly mixed, the cationic emulsifier is added to the aqueous mixture at a temperature of about 80 to 95 ° C under stirring to form a water-in-oil emulsion. The mixing energy input will be high and will be maintained for a sufficient time to form a water-in-oil emulsion that has a uniform appearance (indicating the presence of relatively small micelles in the emulsion).

The water is injected directly into the emulsion to cool it to a temperature of about 45 to about 60 ° C. The temperature is critical. Unstable emulsions result if the temperature falls below about 45 ° C. Higher temperatures favor the unacceptable loss of water through evaporation. During this rapid cooling step, the emulsion, initially water-in-oil, is inverted to form an oil-in-water emulsion. An aqueous solution of weakly acidic material is then added to the oil-in-water emulsion. Attempts to add the acidic material prior to the formation of the emulsion produced emulsions that were thin and granular. It is important for the stability of the emulsion that the pH of the solution be within the range of about 2 to 4, preferably 3 to 3.8. It is better not to "shake" the emulsion by the addition of more concentrated acids and by variable temperatures. Accordingly, the temperature of the acid solution should be from about 45 to about 55 ° C. The weakly acidic material is added to the formulation as an aqueous solution having a pH (measured at 25 ° C) within the range of about 2 to about 4, preferably about 3.8, according to the method of this invention. Therefore, it may be necessary to adjust the pH of the selected acid. The pH adjusting agent is not believed to be strictly critical, although agents that have weak electronegativities are currently preferred. Examples include amines such as triethanolamine and tetrahydroxypropyl ethylenediamine. At present, ammonium hydroxide is particularly preferred. After complete mixing and additional cooling, the mixture is filtered to produce a homogeneous lotion or cream. Water is added at three points during the process: when the aqueous mixture of insoluble water and wetting components is formed, when the water-in-oil emulsion is rapidly cooled and an oil-in-water emulsion is formed, and when the aqueous solution of weakly acidic material is added. The volume of water is added during the rapid cooling step, adding minor amounts with the aqueous mixture of insoluble components in water and humectant and with the weakly acidic material. Preferably about 20% water is added with the aqueous mixture and about 5% is added with the weakly acidic material, the remainder being added during rapid cooling.

The invention will now be described more fully and will be illustrated by the following examples.

Example 1 Preparation of water-in-oil phase The formulation of this Example was prepared in a pilot scale Pfaudler mixing tank (manufacturer's capacity 400 L). This tank has double jacket, with upper and lower heating / cooling jackets. It has a 1.5 hp agitation motor driven on a belt and is equipped with a single blade S-curved mixer. The tank employs a non-removable individual baffle and is equipped with a lower valve that allows the addition of materials below the surface through a positive displacement pump. Additionally, all pH measurements on the final product were made at 25 ° C in 1: 10 dilutions in purified water. Initially, the Pfaudler deposit was loaded with 50.0 kg of purified water. This was stirred and heated to 71 ± 5 ° C. During mixing at 54 rpm speed, 30.0 kilograms (kg) of 99.5% glycerin was added; 250 grams (g) of methyl paraben, 100 g of propyl paraben, 10.0 kg of white petrolatum USP, 7.50 kg of isopropyl palmitate and 3.13 kg of dimethicone 10 cst in that order. After increasing the temperature to 77 ° C, 6.250 kg of cetyl alcohol was added and mixed for 10 minutes. Maintaining the mixing speed at 54 rpm and the temperature of the charge at 77 ° C, 12.5 kg of dimethyl distearyl ammonium chloride (Varisoft TA-103 available from Witco Corp., New York, N.Y.) was added. The mixing was continued at the elevated temperature at 85-90 ° C and the mixing speed was increased to 80 rpm until the dimethyl distearyl ammonium chloride was completely dispersed. Then the heat of the deposit was disconnected.

Example 2 Preparation of acidic material In a separate flask was prepared a mixture of 7.15 kg of 70% glycolic acid and 8.83 kg of 88% lactic acid. To this solution, 2,855 kg of USP ammonium hydroxide were carefully added to achieve a pH of 3.3.

Example 3 Preparation of finished emulsion To the oil-in-water phase of example 1, 111.4 kg of cooling water (cooled to 19.8 ° C in a Mueller stainless steel tank of 200 L coated open at the top) for a period of 47 minutes below the surface through the bottom valve of the Pfaudler tank. The charge temperature was 46 ° C and the mixing speed was reduced to 50 rpm. At this point the acid phase of Example 2 was added below the surface to cool the water / emulsion phase over a period of 30 minutes. When the acid addition was over, the resulting emulsion was mixed for at least 15 minutes. When the temperature had dropped to 38 ° C, the product was finally filtered through a 200 mesh filter screen into a clean retention vessel. The resulting emulsion was creamy and did not separate over time. Example 4 A dry skin hydration study was conducted to compare the humidification capacity of four lotions containing alpha-hydroxy acids with the humidification capacity of a lotion famous for its humidification capacity, but which did not contain alpha hydroxy acid. Lotions containing alpha hydroxy acids were the lotion of Example 3; Jergens. { R) Advanced Therapy Dual Healing Cream from The Andrew Jergens Co. of Cincinnati, Ohio; EUCERIN (R) Plus Alphahydroxy Moisturizing Lotion from Beiersdorf, Inc. of Nor alk, Connecticut; and LUBRIDERM (R) Moisture Recovery Lotion (containing lactic acid) from Warner-Lambert of Morris Plains, New Jersey. CUREL (R) Therapeutic Moisturizing Lotion by Bausch & Lomb Incorporated of Rochester, New York, was the lotion that did not contain alpha hydroxy acids that was compared to the others. Sixteen female participants between 25 and 60 years of age completed the study. At the time of the study they were in relatively good health and had a dry skin classification of at least Grade 2 when examined using the following grading scale: 0 = Soft, without evidence of dryness 1 = Lightly dry skin 2 = Skin Moderately dry, with scales, peeled 3 = Very dry skin, with scales, peeled.

The participants refrained from using humidifiers, creams, lotions and sunscreen products on their legs for a week before the start of the study and also refrained from shaving their legs 72 hours before the start of the study. All participants used ivory soap during the study and for five days before the study. Four pairs of treatment sites were rotated between areas on the legs of each participant (outer aspect of the calf). Each of these areas was divided into two treatment sites. One site received Curel as described below and the other site received one of the four alpha hydroxy acid products. The designated test sites (each 2.5 cm x 2.5 cm each) were treated using a dose of 2 mg / cm2 of the test material applied by a 0.5 cm3 syringe and dispersed over the test area using a finger. Each participant received all the test materials. A fifth site on each leg remained as an untreated control site. The skin moisture levels were tested with a NOVA DPM 9003 instrument that measures the capacitance on the surface of the skin. It has been shown that the electrical capacitance of the surface of the skin is related to the water content of the stratum corneum. Tagami, H., "Impedance Measurement for Evaluation of the Hydration State of Skin Surface", Cutaneous Investigation in Health and Disease, pages 79-111, Marcel Dekker, Inc. (New York), New York, 1989) and Dikstein, S., et al. "Comparison of Different Instruments for Measuring Stratum Corneum Moisture Content", International Journal of Cosmetic Science, Vol. 8, pages 289-292 (1986). Before the study, the test materials were applied to an area of a glass transparency measuring 2.5 cm x 2.5 cm using a finger. After a drying time of 30 minutes, capacitance measurements were made with the NOVA instrument at five minute intervals until the readings were zero. If the values were not zero after a drying time of 30 minutes for any product, the additional time required to reach a zero reading was added to the time of 30 minutes before the first post-treatment reading. This was done to ensure that measurements of the skin capacitance of the participants were not influenced by non-evaporated water or other components of the test materials. The participants remained in a room at a temperature of 20-25 ° C and a relative humidity of 30-40% during the study. After a 30-minute equilibrium period, measurements of transepidermal water loss were made at the untreated control site every 5 minutes until the evaluations were consistent. After obtaining consistent values, baseline measurements were made at all sites using both instruments. The test materials were then applied to the appropriate test sites as described above. The measurements were made in triplicate at 60, 90, 120, 180 and 240 minutes to determine the effect of the test products on the skin's humidification. The average of the three readings was used in the following analysis. Variance analysis techniques of repeated measurements (ANOVA) were used to determine the existence, if any, of significant differences between the treatment partners. This design also evaluated the effect of time as well as the potential for interaction between sample and time. All hypothesis testing was performed at the alpha level = 0.05. The results of NOVA instrument measurements (indicated as capacitance in picofarads) are shown in Tables 1-4 below.

Table 1 shows the lotion of Example 3 compared to CUREL Therapeutic Moisturizing Lotion. The sites treated with the lotion of Example 3 showed higher moisture content of the skin than the CUREL lotion at each instant. TABLE 1 Minutes after application 60 90 120 180 240 Lotion CURL 241.9 240.4 247.0 250.5 246.1 Example 3 333.8 306.8 301.8 296.1 289.9 Table 2 shows the JERGENS Advanced Dual Healing Lotion compared to the CUREL Therapeutic Moisturizing Lotion. The sites treated with the JERGENS lotion showed higher moisture content of the skin than the sites treated with CUREL in the instant of 60 minutes, but the lotions acted similarly in the other instants.

TABLE 2 Minutes after application 60 90 120 180 240 Lotion CUREL 234.5 226.3 239.4 232.5 231.7 Lotion JERGENS 291.1 245.0 245.4 231.3 229.0 Table 3 shows the EURCERIN Plus Alphahydroxy Moisturizing Lotion compared to the CUREL Therapeutic Moisturizing Lotion. The sites treated with the lotion EURCERIN showed higher moisture content than the sites treated with CUREL at each moment.

TABLE 3 Minutes after application 60 90 120 180 240 Lotion CUREL 250.6 221.8 232.8 229.2 240.8 Lotion EUCERIN 330.3 279.6 276.0 262.0 268.8 Table 4 shows the LUBRIDERM Moisture Recovery Lotion compared to the CUREL Therapeutic Moisturizing Lotion. The sites treated with the CUREL lotion showed higher moisture content than the sites treated with the LUBRIDERM lotion at all times, except for the 60 minute instant.

TABLE 4 Minutes after application 60 90 120 180 240 Lotion CURL 255.9 249.8 259.9 260.6 251.2 Lotion LUBRIDERM 276.5 225.0 214.7 202.8 194.3

Claims (33)

1. CLAIMS 1. An oil-in-water emulsion for the treatment of the skin that includes: (a) from about 2 to about 10% by weight of a quaternary ammonium compound having the formula GO. where Rx and R2 are each long chain, substantially linear alkyl groups having from about 16 to about 22 carbon atoms, R3 and R4 are each lower alkyl groups having from about 1 to about 3 carbon atoms and X is a salt-forming anion; (b) from about 1 to about 40% by weight of a water-soluble humectant, substantially non-ionizable; and (c) a weakly acid, pharmaceutically acceptable material having a dissociation constant (pKa) in the range of about 1 to about 6, the acidic material being provided in an amount sufficient to adjust the pH of the finished emulsion to a value in the range of about 2.5 to about 4.5, when the emulsion is diluted with purified water up to 10 times its weight. The composition of claim 1, wherein the emulsion contains from about 3 to about 8% by weight of the quaternary ammonium compound. The composition of claim 1, wherein the salt-forming anion of the quaternary ammonium salt is selected from the group consisting of chloride, bromide, or iodide. 4. The composition of claim 3, wherein the anion is chloride. The composition of claim 1, wherein the quaternary ammonium compound is dimethyl distearyl ammonium chloride. The composition of claim 1, wherein the humectant is selected from the group consisting of propylene glycol, polyethylene glycol, sorbitol, and glycerin. 7. The composition of claim 1, wherein the humectant is glycerin. The composition of claim 7, wherein the emulsion contains from about 1 to about 20% by weight of glycerin. The composition of claim 1, wherein the dissociation constant of the weakly acidic material is within the range of about 2.5 to 5.0. The composition of claim 1, wherein the dissociation constant of the weakly acidic material is greater than the pH of the finished emulsion. The composition of claim 1, wherein the pH of the finished emulsion is within the range of about 3.0 to about 4.0. The composition of claim 1, wherein the weakly acidic material is an alpha hydroxy acid described by the formula OH I R5 ~ C - COOH I R6 where R5 and R6 are aliphatic hydrocarbon groups and ester having from 1 to 10 carbon atoms. 13. The composition of claim 12, wherein the alpha hydroxy acid is selected from the group consisting of citric acid, glycolic acid, glucuronic acid, galacturonic acid, alpha hydroxybutyric acid, alpha hydroxyisobutyric acid, lactic acid, malic acid, mandelic acid, mucic acid, pyruvic acid, alpha phenylactic acid, alpha phenylpyruvic acid, saccharic acid, tartaric acid, tartronic acid, and mixtures thereof. The composition of claim 12, wherein the alpha hydroxy acid is selected from the group consisting of glycolic acid, lactic acid, tartaric acid, malic acid, and mixtures thereof. The composition of claim 1, wherein the acidic material is selected from the group consisting of citric acid, glycolic acid, glucuronic acid, galacturonic acid, alpha hydroxybutyric acid, alpha hydroxyisobutyric acid, lactic acid, malic acid, mandelic acid, acid mucic, pyruvic acid, alpha phenylactic acid, alpha phenylpyruvic acid, saccharic acid, tartaric acid, tartronic acid, and mixtures thereof. The composition of claim 1, wherein the acidic material is selected from the group consisting of glycolic acid, lactic acid, and mixtures thereof. 17. The composition of claim 1, wherein the emulsion is prepared in the substantial absence of added salt. 18. The composition of claim 17, wherein the total salt concentration of the emulsion is not more than about 0.5 molar. The composition of claim 1, wherein the emulsion further comprises a petrolatum or mineral oil. The composition of claim 1, wherein the emulsion additionally comprises a fatty alcohol. The composition of claim 1, wherein the emulsion additionally comprises a fatty ester emollient. The composition of claim 1, wherein the emulsion further comprises a silicone oil or fluid having a viscosity in the range of about 5 to about 12,500 centistokes. The composition of claim 1, wherein the emulsion contains from about 30 to about 90 weight percent water. The composition of claim 10, wherein the emulsion contains from about 55 to about 85 weight percent water. 25. The composition of claim 1, further comprising: (a) from about 1 to about 10% by weight of petrolatum or mineral oil; (b) from about 1 to about 8% by weight of a fatty alcohol; (c) from about 1 to about 8% by weight of a fatty ester emollient; and (d) from about 0.1 to about 5% by weight of a silicone oil or fluid having a viscosity of about 5 to about 12,500 centistokes. 26. The composition of claim 14, wherein the weakly acidic material is selected from the group consisting of glycolic acid, lactic acid, and mixtures thereof. The composition of claim 25 or 26, wherein the quaternary ammonium compound is dimethyl distearyl ammonium halide. 28. The composition of claim 25 or 26, wherein the humectant is glycerin. 29. The compositions of claims 25 or 26, wherein the fatty alcohol is cetyl alcohol and the fatty ester emollient is isopropyl palmitate. 30. A method for preparing an oil-in-water emulsion containing water-insoluble components, a water-soluble humectant, and a cationic emulsifier, which method comprises: (a) providing an aqueous solution of a weakly acidic material having a pKa within the range of about 1 to about 6, said solution having a pH in the range of about 2 to about 4; (b) forming an aqueous mixture of the water insoluble components and the humectant; (c) adding the cationic emulsifier to the aqueous mixture at a temperature of about 80 to about 95 ° C, to form a water-in-oil emulsion; (d) cooling the emulsion formed in step (c) to a temperature within the range of about 45 to about 60 ° C, by direct injection of purified water, thereby causing a phase inversion and forming an oil emulsion -in-water; and (e) adding said aqueous solution of weakly acidic material at a temperature in the range of about 45 to about 55 ° C to the emulsion formed in step (d) to produce an oil-in-water emulsion having a pH within the range of about 2.5 to about 4.5 when diluted with purified water to 10 times its weight. The method of claim 30, wherein the aqueous solution provided in step (a) has a pH in the range of about 3 to about 3.8. 32. The method of claim 30, wherein the cationic emulsifier is added to the aqueous mixture at a temperature of about 84 to about 88 ° C. The method of claim 30, wherein the emulsion formed in step (c) is cooled to a temperature in the range of about 52 to about 55 ° C.