Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Cosmetic – antiperspirant – dentifrice
Reexamination Certificate
2000-01-24
2002-08-27
Dees, Jose′ G. (Department: 1616)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Cosmetic, antiperspirant, dentifrice
C514S059000, C514S060000, C514S844000, C514S938000
Reexamination Certificate
active
06440432
ABSTRACT:
FIELD OF THE INVENTION
Cosmetic compositions for human skin containing a dextran or maltodextrin and a weak carboxylic acid.
BACKGROUND OF THE INVENTION
Cosmetic products which improve the appearance of skin are increasingly popular with consumers. Frequently, consumers seek to alleviate or delay the signs of aged or photoaged skin, such as fine lines and wrinkles, dry and sagging skin. Consumers also seek other benefits in addition to anti-aging.
Some ingredients used in topical products are potentially irritating, especially to people with “sensitive skin.” Such irritation is commonly perceived as sting or burning.
As an example, hydroxy acids and several other weak carboxylic acids have been proven to deliver cosmetic benefits, such as improvement in the appearance of photodamaged or naturally aged skin, skin lightening, treatment of age spots, etc. Unfortunately, their use at high concentrations may occasionally be associated with skin irritation, e.g. skin redness and stinging sensation upon application. For aesthetic reasons, these actives are most often delivered as oil-in-water emulsions. Practically, the final composition pH should be higher than 3 in order to prevent deleterious effects to skin tissues and unacceptable levels of irritation. Water soluble weak acids when delivered from an oil-in-water emulsion at acidic pH often induce high levels of sting. The sting occurs immediately after application, reaches a maximum intensity usually by 5-8 minutes after application and then begins to reduce in intensity.
The irritation can be ameliorated by lowering the amount of an active ingredient in the composition or by reducing the active's penetration through the skin. A serious drawback of both approaches is that the efficacy is impaired. The weak acid related irritation can be reduced by raising the composition's pH but this method yields reduced efficacy due to a decreased acid penetration through the skin. It is desirable to reduce or eliminate the irritation potential of weak acids while maintaining their efficacy.
The need exists, therefore, for a composition and method that prevents or reduces the skin irritation.
Coury et al. (U.S. Pat. No. 5,618,850) discloses cosmetic compositions containing polyhydroxy acids conjugated to the dextran polymer. EP 691126 (Beiersdorf) discloses cosmetic compositions with low stinging potential for treatment of sensitive skin. The compositions contain pigment to sequester AHA. A serious shortcoming of the Coury and Beirsdorf disclosures is that conjugation or sequestration significantly reduces delivery of the active and its efficacy. Most actives in current use have molecular weight less than 1000 Dalton. The penetration of actives through the skin decreases strongly with its molecular weight (Ref: Transdermal Delivery of Drugs; Volume III, P 7-8. Agis F. Kydonieus and Bret Berner (ed) CRC Press, Inc Boca Raton, Fla., 1987). Polymers have high (>>1000 Dalton) molecular weight. Conjugation of actives with the polymer Dextran will make it a high molecular weight molecule and hence will significantly lower penetration.
Sequestration of the weak acid will reduce the amount of acid that would be available for delivery.
Another approach to lower the sting is to formulate the acid with a strong alkali metal base. Yu et al. (U.S. Pat. No. 4,105,783) suggested the use of ammonium hydroxide or an organic base. Unfortunately, this method raises the pH of the composition and reduces the ability of the weak acid to penetrate the skin, thus lowering its efficacy (see Sah et al. in
J. Cosmet. Sci
. 49, 257-273, 1998).
A clear need exists for a cosmetic composition with a weak acid that reduces sting but does not reduce dermal delivery.
Publication from LAREX (Mar. 23, 1998) discloses the use of a polysaccharide (arabinogalactan) to increase the exfoliation performance of a skin care lotion containing alpha hydroxy acid by 80% and to do so without increased irritation. The present invention, however, aims to decrease irritation, rather than merely not increasing it. It has been found, as part of the present invention, that other polysaccharides, dextran and maltodextrin, decrease irritation associated with the use of weak carboxylic acids, whereas arabinogalactan does not have this effect. Additionally, it has been found that dextran, unlike arabinogalactan, enhances the anti-aging efficacy of hydroxy acids.
SUMMARY OF THE INVENTION
The present invention includes a skin cosmetic composition comprising:
(i) from about 0.5 to about 20 wt. % of a dextran or maltodextrin;
(ii) from about 0.01 to about 20 wt. % of a weak carboxylic acid having pKa of above about 2; and
(iii) a cosmetically acceptable vehicle.
The invention also includes cosmetic methods of stimulating collagen synthesis by fibroblasts and keratinocyte differentiation in the skin, by applying to the skin the inventive composition.
The invention also includes a cosmetic method of treating or delaying aged, chronoaged, photoaged, dry, lined or wrinkled skin, increasing stratum corneum firmness and flexibility, improving skin tone, and generally increasing the quality of skin by applying to the skin the inventive composition.
The invention further provides a method for reducing skin irritation caused by the topical application of a composition containing a weak carboxylic acid, the method comprising topically applying a dextran or maltodextrin in a cosmetically acceptable vehicle. Thus, according to this inventive method, the dextran or maltodextrin may be co-present with a weak acid in the same composition, or it may be applied from a separate composition.
DETAILED DESCRIPTION OF THE INVENTION
Except in the operating and comparative examples, or where otherwise explicitly indicated, all numbers in this description indicating amounts of material or conditions of reaction, physical properties of materials and/or use are to be understood as modified by the word “about.” All amounts are by weight of the oil-in-water emulsion, unless otherwise specified.
The term “skin” as used herein includes the skin on the face, neck, chest, back, arms, armpits, hands and scalp.
The terms “irritation,” “sting,” and “burn,” “inflammation,”, and “redness” as used herein are synonymous and are used interchangeably.
The molecular weight is expressed in Dalton (D). The numerical terms followed by letters “KD” denote molecular weight of a compound, to be read as the numerical term ×1,000 e.g. 10 KD means molecular weight of 10,000 D).
Dextran
Both dextran and maltodextrin are glucose homopolymers.
Dextran is a beta-1,6-glucan with several glucose side chains, bound primarily to the main chain of the macromolecule through 1,3-linkages but, in part also by 1,4- and 1,2- linkages. On the average, 95% of the glucose residues are present in the main chain. It is produced by certain bacteria from a nutrient medium containing saccharose. The molecular weight of dextrans generally ranges from 5 KD to 2,000 KD, preferably from 5 KD to 1,000 KD, to maintain anti-iiritation efficacy, yet to minimize increase in formulation viscosity.
Maltodextrin
Maltodextrins (C
6
H
10
O
5
)
n
·H
2
O (CAS Reg. No. 9050-36-6 are non-sweet nutritive saccharide polymers that consist of D-glucose units linked primarily by alpha-1,4-bonds, having a DE (Dextrose Equivalence) less than 20. They are prepared as a white powder or concentrated solution by partial hydrolysis of corn starch with safe and suitable acids and/or enzymes. The suitable source of maltodextrin is Maltrin® from Grain Processing Corp. Matrin® contains maltodextrin and corn syrup solids.
The amount of dextran or maltodextrin in the inventive composition ranges from 0.5 to 20%, preferably from 1 to 15%, most preferably from 1 to 10%, by weight of the composition.
Weak Carboxylic Acid
A weak carboxylic acid suitable for use in the inventive compositions is an acid with dissociation constant, pKa, of above about 2. Preferably, the pKa is above about 3, most preferably in the range of from about 3 to about 5.
The Concept of pKa
An acid is a species having
Habif Stephan Samuel
Mukherjee Surajit
Rick Donald
Weinkauf Ronni Lynn
Dees Jose′ G.
Lamm Marina
Plotkin Ellen
Unilever Home & Personal Care USA a division of Conopco, Inc.
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