Skin penetration of cosmetic ingredients.

A decade ago, generally recognized wisdom among cosmetic chemists suggested that the skin was a well nigh impenetrable barrier, that chemicals and fragrance materials performed their function while remaining safely ensconsed among the topmost layers of the stratum corneum. Sensitivity and irritation, where encountered, were regarded as surface phenomena--even where there was a suggestion of hair follicle involvement.

There were, of course, exceptions. For antiperspirants, deposit of the aluminum salts as a sort of "plug" in the sweat gland duct openings was regarded as essential to the function of the products, though research dermatologists such as Dr. Albert Kligman (University of Pennsylvania) were quick to point out that even the optimum formulations reduced sweating by only about 55 percent. And, a decade ago Dr. Kligman was also suggesting that the formation of that plug in the sweat gland opening might take 24 hours to complete--indicating that daily bathing might be undermining the functioning of a product that has become a principal after-bath ritual in the U.S.

But the major …