Drug – bio-affecting and body treating compositions – Designated organic active ingredient containing – Having -c- – wherein x is chalcogen – bonded directly to...
Reexamination Certificate
1998-09-02
2001-05-29
Jarvis, William R. A. (Department: 1614)
Drug, bio-affecting and body treating compositions
Designated organic active ingredient containing
Having -c-, wherein x is chalcogen, bonded directly to...
Reexamination Certificate
active
06239174
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a water-in-oil (W/O) emulsion containing ascorbic acid, to the use of this emulsion for topically treating the skin, on the face, including the area around the eyes, on the body and on the scalp of human beings, as well as to a process for treating the skin topically using this emulsion.
2. Description of the Background
It has been sought for a long time to stabilize ascorbic acid, or vitamin C, in appropriate pharmaceutical presentations, on account of its beneficial properties. This is because ascorbic acid has many biological functions, such as the stimulation of collagen synthesis, the strengthening of skin tissues against external attacking factors, depigmentation, its anti-free-radical activity, and the compensation for vitamin E deficiency.
However, on account of its chemical structure (&agr;-keto lactone), ascorbic acid is very sensitive to the influence of environmental parameters such as light, oxygen and water. This results in an unavoidable degradation over time of ascorbic acid in solution form leading to a loss of its activity. Moreover, degradation, even slight, of the ascorbic acid, causes yellowing of a composition containing it.
To reduce or delay the degradation of ascorbic acid in solution form, it has been recommended in U.S. Pat. No. 5,140,043 to introduce it into aqueous-alcohol solutions, formed of at least 80% water and having a pH of less than 3.5. However, repeated application of solutions of strongly acidic pH to the skin can disrupt the skin's equilibrium and in particular cause skin irritation.
Moreover, EP-A-670,157 describes the stabilization of vitamin C in a W/O emulsion having a pH of not more than 3.5 and containing, as emulsifier, a dimethicone-copolyol and/or an alkyldimethiconecopolyol. Such a W/O emulsion is better tolerated by users than an aqueous-alcoholic solution, since the aqueous acidic phase containing ascorbic acid is applied in small amount to the skin, in the form of fine droplets dispersed in the oil, which causes no skin irritation or burning. However, repeated application of a composition of acidic pH can have drawbacks for individuals with sensitive skin.
In addition, WO-A-95/28092 discloses stabilizing active agents, such as enzymes or vitamins, in a water-in-oil emulsion containing a high concentration of polyols and an emulsifier chosen from monoglycerides and polyglyceryl ricinoleate. However, the emulsions described in this application contain less than 10% water, and there is still a need for emulsions which can contain more water while at the same time maintaining good stability of the ascorbic acid.
While, it is Inown that the pH has an influence on the stability of ascorbic acid. Thus, the article by B.R. Hajratwala entitled “Stability of ascorbic acid”, published in Revue Sciences Pharmaceutiques on Mar. 15, 1985, shows that the decomposition of ascorbic acid exhibits minima at pH 2.5-3 and at pH 6. However, all the tests presented in that article are carried out using simple solutions of ascorbic acid in water and a person skilled in the art cannot deduce therefrom the behavior of ascorbic acid in an emulsion, in which the interactions of the oils and the surfactants modify the environment appreciably and unpredictably. In addition, prior literature in the cosmetics field encourage those skilled in the art to use an acidic pH (see U.S. Pat. No. 5,140,043 and EP-A670157, mentioned above).
The need thus exists for a composition which can be used in the cosmetics and/or dermatological fields, in which ascorbic acid is stable and which causes no skin irritation after application, even for individuals with sensitive skin.
SUMMARY OF THE INVENTION
The present invention is based, in part, on the surprising discovery that stability of ascorbic acid is considerably improved by incorporating ascorbic acid, or a salt thereof, into a water-in-oil emulsion containing a silicone-based surfactant, where the aqueous phase of the emulsion has a pH of 5.5 to 7.5, and that such a composition is very well tolerated by human skin.
Accordingly, the present invention provides a water-in-oil emulsion containing ascorbic acid and comprising an aqueous phase dispersed in an oily phase using at least one silicone-based emulsifier, where the aqueous phase has a pH ranging from 5.5 to 8, preferably equal to 6.
Thus, it has been found, surprisingly, that, in contrast with the teaching of that article according to which ascorbic acid in solution behaves very differently in aerobic medium and in anaerobic medium, the degradation of ascorbic acid in an emulsion according to the invention is the same, whether the medium be aerobic or anaerobic.
In the emulsion according to the invention, the pH is preferably equal to or close to 6. This pH is close to the skin's pH; this results in great compatibility of the emulsion of the invention with the skin.
The emulsion according to the invention allows the degradation of ascorbic acid to be avoided and thus stabilizes it. Thus, another subject of the present invention is the use of the emulsion as defined above to stabilize ascorbic acid.
The present invention also provides a method of tonifying and regenerating skin, smoothing out fine lines on the skin, improving the complexion of skin, removing skin pigmentation mark, combating the harmful effects of UV radiation, and/or to strengthening skin tissues against environmental attack, by applying the inventive emulsion to skin.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The ascorbic acid concentrations in the emulsion of the invention are those used conventionally in the cosmetics and dermatological fields and, for example, from 0.01 to 20%, preferably from 0.1 to 10% and better still from 0.5 to 5%, of the total weight of the emulsion. These ranges include all specific values and subranges therebetween, including 0.02, 0.05, 0.2, 1, 2, 3, 8, 12, 15 and 18% by weight. The ascorbic acid may be in the form of a salt. Preferred salts are alkali and alkaline earth metal salts of ascorbic acid (e.g., sodium, potassium, magnesium and/or calcium salts).
The silicone-based emulsifier is a compound having at least one silicone moiety. The silicone-based emulsifier is preferably chosen from dimethiconecopolyols and alkyldimethicone-copolyols. These emulsifiers preferably comprise fully oxyethylenated polyether groups. However, it is also possible to use emulsifiers having partially oxyethylenated polyether groups.
Advantageously, the weight percentage of polyether relative to the total weight of the emulsifier is chosen from 1 to 50%, preferably from 15 to 35%, in the case of dimethicone-copolyols, and from 1 to 5%, preferably from 2 to 3%, in the case of alkyldimethicone-copolyols. These ranges include all specific values and subranges therebetween, including 4, 10, 20, 25, 30, 35,40 and 45% by weight.
As dimethicone-copolyol which can be used in the emulsion according to the invention, mention may be made of the mixture of dimethicone-copolyol and cyclomethicone sold under the name “Q2-3225C” by Dow Corning and the product sold under the name “SF-1228” by General Electric.
As alkyldimethicone-copolyol which can be used in the emulsion according to the invention, lauryldimethicone-copolyol can be used, for example such as the product sold under the name “Q2-5200” by Dow Corning, and cetyldimethicone-copolyol, for example such as the product sold under the name “Abil EM 90” by Goldschmidt.
Other dimethicone-copolyols and alkyldimethicone-copolyols which may be used in the present invention are listed in
International Cosmetic Ingredient Dictionary and Handbook
, Volume 2, pages 1593-1595 (Seventh Edition, published by The Cosmetic, Toiletry, and Fragrance Association, 1997), incorporated herein by reference.
The emulsifiers are, for example, present in the em
Afriat Isabelle
Chanvin Florence
Jarvis William R. A.
Kim Vickie
L'Oreal
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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