Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – For cleaning a specific substrate or removing a specific...
Reexamination Certificate
2000-10-20
2002-11-26
Hess, Bruce H. (Department: 1774)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
For cleaning a specific substrate or removing a specific...
C510S159000, C510S405000, C510S470000, C510S477000, C510S488000, C510S505000
Reexamination Certificate
active
06486106
ABSTRACT:
The present invention relates to compositions for topical application to the skin surface, in particular to skin wash compositions which are applied to water-wetted skin and subsequently rinsed off with water. Specifically, the present invention relates to skin wash compositions comprising an &agr;-hydroxy acid as an active ingredient formulated in a mild and non-irritant detergent base.
The class of compounds generally known in the field of cosmetic and therapeutic skin treatments as &agr;-hydroxy acids includes compounds such as salicylic acid, lactic acid and glycolic acid. These compounds constitute the active ingredients of a number of commercially available products which are applied to the skin in order to confer a beneficial effect with respect to appearance and skin condition, in particular smoothness and suppleness. Salicylic acid for example has been shown to have keratolytic and comedolytic activity as well as anti-bacterial efficacy and has been used in the treatment and prevention of mild to moderate acne for more than 100 years. Lactic acid has a beneficial effect on skin hydration and is a constituent of a number of skin tonic and moisturising products.
&agr;-Hydroxy acids, whilst conferring a beneficial effect on the skin, may cause local irritation when applied to sensitive areas of the skin, in particular the face. Moreover, local irritation may be exacerbated by the carrier system in which the active ingredient is formulated. For example, skin wash compositions and in particular face wash compositions which are generally formulated with a soap-free detergent base selected for effective cleansing and foaming, may confer an irritant effect due to the use of ionic surfactants commonly employed in such detergent systems.
A further problem associated with formulating compositions containing &agr;-hydroxy acids arises because of the desirability to formulate the composition at an acid pH at which the most efficacious free-acid form of the &agr;-hydroxy acid will predominate. For skin wash compositions, this problem is exacerbated by the difficulty of obtaining a detergent base system at sufficiently low pH. A skin wash composition described as having a gentle yet effective cleanser for acne treatment and containing 2.0% w/w salicylic acid in a detergent base comprising a mixture of anionic and amphoteric surfactants is commercially available. Analysis of this product shows that it has a pH of 5. It follows, having regard to the pKa of salicylic acid which is attributed the value 2.97, that the free-acid form of the &agr;-hydroxy acid does not predominate in this product and that its efficacy is accordingly not fully optimised.
It is an object of the present invention to provide a skin wash composition containing an &agr;-hydroxy acid and a detergent base which has good cleansing and foaming characteristics, is mild and non-irritant and wherein the pH of the composition approaches the pKa of the &agr;-hydroxy acid such that the efficacy of the &agr;-hydroxy acid is enhanced. This object is achieved according to the present invention which is based on the unexpected finding that a detergent base comprising a mixture of a non-ionic alkylpolyglucoside surfactant and an amphoteric surfactant not only has the desired cleansing and foaming characteristics and is mild and non-irritant when applied to the skin but also enables compositions to be formulated at low pH.
According to the present invention there is provided a skin wash composition comprising from 0.1 to 10% w/w of an &agr;-hydroxy acid and a detergent base consisting of a mixture of a non-ionic alkylpolyglucoside surfactant and an amphoteric surfactant wherein the pH of the composition is in the range 3.0 to 4.5.
Suitable &agr;-hydroxy acids for incorporation into skin wash compositions of the invention include salicylic acid, lactic acid, citric acid, glycolic acid, malic acid, maleic acid, pyruvic acid and hydroxy-octanoic acid. Preferred &agr;-hydroxy acids are salicylic acid, lactic acid and glycolic acid, especially salicylic acid and lactic acid. Salicylic acid will suitably be present in compositions of the invention at a concentration in the range 0.2 to 5.0% w/w, more suitably in the range 1.0 to 3.0% w/w. A preferred concentration for salicylic acid is 2.0% w/w. Lactic acid will suitably be present in compositions of the invention at a concentration in the range 0.1 to 5.0% w/w, more suitably in the range 0.5 to 2.5% w/w. A preferred concentration for lactic acid is 1% w/w. Glycolic acid will suitably be present at a concentration in the range 2.0 to 10.0% w/w.
As used herein, the term alkylpolyglucoside surfactant means a non-ionic surfactant derived from common natural organic monomer units as found in starch, fats and sugars, and most suitably derived from D-glucose monomer units. Alkylpolyglucosides derived from D-glucose are acetal compounds in which the alkyl residue has a carbon chain length of from 8 to 16 carbon atoms and the degree of glucosidation (or polymerisation), i.e., the average number of glucose units per alkyl radical, is between 1.1 and 6. A range of suitable alkylpolyglucosides are commercially available either individually or as mixtures or blends. Compositions according to this invention will generally contain mixtures or blends of different alkylpolyglucosides. Preferred alkylpolyglucosides for use in the present invention include decyl glucoside and lauryl glucoside and mixtures thereof. Alkylpolyglucoside surfactants generally comprise up to 20% w/w of the skin wash composition, suitably from 2.0 to 15.0% w/w and preferably from 4.0 to 10.0% w/w of the composition. It will be appreciated that the amount of alkylpolyglucoside will be determined to some extent by the nature and amount of amphoteric surfactant present in the composition.
In principle, any amphoteric surfactant which is acceptable for topical application to the skin may contribute, with the alkylpolyglucoside surfactant, to the detergent base but, in view of their inherent mildness and good foaming performance, the preferred amphoteric surfactant will belong to the class of compounds known as betaines. Structurally, betaine compounds contain a carboxylate functional group and a quaternary nitrogen function separated by a methylene moiety. They include n-alkyl betaines such as cetyl betaine and behenyl betaine, and n-alkylamido betaines such as cocoamidopropyl betaine. The amphoteric surfactant component of the detergent base for compositions of the present invention may be a single compound or a mixture of blend of two or more different substances. A preferred amphoteric surfactant is cocoamidopropyl betaine. Amphoteric surfactants will generally comprise up to 10% w/w of the skin wash composition, suitably from 2.0 to 8.0% w/w and preferably from 2.5 to 6.0% w/w of the skin wash composition. The amount of amphoteric surfactant will to some extent be determined by the alkylpolyglucoside surfactant component of the detergent base.
Typically, the detergent base consisting of the mixture of non-ionic alkylpolyglucoside surfactant and amphoteric surfactant will constitute up to 30% w/w of the skin wash composition. Suitably the detergent base will constitute from 5.0 to 20.0% w/w and more suitably from 8.0 to 18.0% w/w of the skin wash composition.
Control of pH to within defined limits is an essential feature of the present invention. A pH within the desired range 3.0 to 4.5 is conferred partly by the inherent properties of the &agr;-hydroxy acid and specific surfactants and quantities thereof making up the detergent base and partly, where required, by use of a suitable neutralising agent for the &agr;-hydroxy acid. Any topically acceptable neutralising agent which is compatible with the other components of the composition can be used. It has been found that the neutralising agent tromethamine is particularly suitable for skin wash compositions containing &agr;-hydroxy acids. Other suitable neutralising agents include sodium hydroxide and triethanolamine. The amount of neutralising agent will be determined by the
Charlton Lynda Rosemary
McGillycuddy Juliet Teresa
Owen Sharon
Garrett Dawn
Hess Bruce H.
SmithKline Beecham p.l.c.
Stein-Fernandez Nora
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