In the field of human skin care, talc, which is a natural hydrous magnesium silicate, is the most important ingredient in most body powders. The excellent slip characteristics of a cosmetic grade of platelet talc provides a lubricant action between touching skin surfaces such as in the groin, axilla, neck and buttocks.
However, because pure talc powder does not absorb moisture well, many have employed powders consisting chiefly of starch and fragrance, with 0.05 methylbenzonium chloride often added for antiseptic action.
The starches do not slip or disperse as readily as talc but they have an excellent moisture absorbent quality. They are soft, white, odorless, nontoxic materials of small particle size, rice starch granules having an average diameter of 3 to 8.mu. and cornstarch granules about 15.mu..
The principal defect of starch is that it combines avidly with moisture and thus tends to become pasty, collecting in the groin and other folds, where it produces irritation. In addition, moist starch is an excellent culture medium for C. ALBICANS, a yeast-like fungus responsible for a severe form of diaper dermatitis in infants. For these reasons, Pediatric Dermatologists do not recommend pure cornstarch as a baby powder.
Attempts have been made to modify the starch granules both to decrease as well as to increase moisture absorbency. In order to decrease moisture absorbency, a chemically modified cornstarch known as Dry-Flo has been used. This is an aluminum salt of a low-substituted alkenyl succinic half-ester of starch. In order to increase the moisture absorbency of starch, others have used a pregelatinized starch. (U.S. Pat. No. 4,485,092).
Acid buffers have also been used in baby powders to counteract the alkalinity of talc, which in the unbuffered state has a pH of 9.0 to 9.3, considered by some as too alkaline for a baby's skin. Boric acid in 5% strength has long been used for this purpose and appears to help keep the pH of diaper just on the acid side of neutral. However, because of the toxicity of boric acid in more concentrated forms, Pediatric Dermatologists prefer that it not be used at all in baby skin powder preparations.
While non-toxic organic acids have been added to talc powder and to other skin care products, they have all been used in ways not related to use in accordance with the present invention. Thus, Tukamoto et al (Chem. Abstracts, Vol. 80, 87415, 1974) studied the stability of ascorbate salts in talc preparations, concluding that the calcium salt was most stable, next to that of the free acid, at the conditions specified. Also, 20% citric acid has been used to bind a polymer to talc powder to improve perfume retaining properties and heat stability. (Japanese Patent No. 57,145-007-1982). Still another publication (German patent No. 2,600,498) describes an aqueous solution of 0.5-3.0% NaCl in 0.2-1.0% lactic acid, thickened with carboxymethylcellulose for use in moistened wipes to clean the ano-genital areas of babies.
Another German patent No. (2,703,642) describes the addition of organic acids to body deodorants as a means of preventing bacterial decomposition of sweat, thus enchancing deodorant action.
The use of a buffer system is disclosed in British Patent No. 1,357,731 issued in 1970 to Lake who claimed success in maintaining a pH of 6.5 in the presence of 0.065N ammonia. The drawbacks to this approach include the fact that the buffer system alone accounts for 45% by weight of the finished powder composition, thus severely compromising the virtues of the inert ingredients (a) starch (added for softness and moisture absorption qualities) and (b) talc (necessary for its excellent slippage and lubricant qualities.) Moreover, this method requires the addition of an antibacterial agent such as BACTERIOSTAT or hexachloraphene, something obviated in the present invention.
Calcium undecylenate is an antifungal agent which also serves as a hydrophobic lubricant and water repellent. In the presence of moisture, this salt releases free undecylenic acid which is both antifungal and antibacterial.
The strengths of undecylenate used in powders at present varies from 20% in a popular foot powder, to 10% in one commercial baby powder. For the purpose of this invention, 3-6% calcium undecylenate is preferable.
The perfumes useful in this invention are any commercial perfume which results in a fragrance desired by the make of this powder composition.
Among the perfume components used in commercial perfume mixtures are: oil of lemon, cananga, sandalwood, copaiba, orange, nutmeg, geranium and lavender; as well as methyl gamma ionone, hydroxycitronellal, benzyl isoeugenol, musk ketone, ylang ylang oil, hexylcinnamic aldehyde, tetrahydro linalool, resin balsam fir, to name only a few.
The proper strength of fragrance is well known to those skilled in the art, and in powder preparations designed especially for babies, the least amount of fragrance necessary is generally used. According to Barnett, the fragrance in baby powder should be present in the 0.20%-0.25% range.