EVALUATION OF ANTIDANDRUFF FORMULATIONS 137 cutis. Another basic structural dissimilarity that may be responsible for a difference in epidermal desquamation is the relative lack of sweat glands in the animal skin, except in special areas. Animals like the cat and dog do not regulate their body temperature by evaporation of water from the entire body surface hence there is no flow of water to wash continuously against and through the cellular structure, as is the case with the human epidermis. It is quite apparent from Fig. 2 that rabbit and guinea pig i½.. • .•,.. -',,,•$%"•.•.. -....•. .... .. ß ....... •:...., -.•- . ...: ..... :. % ..•.• . .• .:. .: •..,. -• •...... .: .',.:::. - .-' •':. •'•3•- • .½' ':: " :•..• "• •:: - •. ---•'-...• .. .: .......• ..... -'• • : .,.. '...'-. , . : :"' .}• .. .. :.... :.:-: -• :' .• ..•, . . *'.•. :• '•.., ... ..... •...: ,.. '-,.-**•...:- .. ß :: . . ..... ..'-.:• :,• -, ,.•:: --.• •. :.•::'•. ' ' ß •.•-'•½'•-.'• ' ,,• ,7' .. ', •,. "...'• -% ........ -.•. •.:' • • - '•½•-•• Figure 9.--Skins of Animals. (Credit: H. J. Spoor, Proc. Sci. Sect. Toilet Goods/lssoe. No. $6, 20 (1961).) skins are very different from human skin. The epiderms are so thin that it takes an extremely competent technician to obtain an adequate section. Calf skin approaches human more closely, but the hair structure is quite different. Pig skin, in thickness of epidermis is quite comparable to human, but the bristle structure is totally foreign. Normal human skin has a reasonably consistent epidermal thickness varying from 0.06 to 0.09 mm. except on the palms and soles (1), and is structurally quite similar in the infant and adult except for acquired maturity of dermal fibers. However,

138 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS the epidermis does respond quickly to irritation. The section labeled "eczema" shows a maximum thickness reached by one epidermis before frank eczematization and exfoliation occurred. Seborrheic eczema could appear this way. Another important factor influencing dandruff formation is the amount and type of sebum secreted. This emollient, when properly dispersed, can smooth and flatten out dry horny skin layers without affecting normal desquamation. However, should sebum become excessive or accumulate at the pore openings the desquamating scale may adhere i• visible oily masses. Dandruff is most apparent on the scalp or other hairy areas because sebaceous glands surround hair follicles and the sebum is discharged upon the hair shaft as a lubricant and protective coating. Sebaceous secretions also furnish lubrication to the non-hairy skin, but here the emollient is discharged directly upon the skin surface through pore open- ings that are associated with lanugo or primitive hairs. The oil is dis- persed more broadly than in the hairy areas. The amount of sebum is influenced by the individual's genetic pattern, nutritional state and endo- crine balance. Usually dark skinned individuals secrete more sebum than do those with lighter skins, the younger adult has more skin oil than the older and the male more than the female. Nutritionally, variation in :the intake of fats or their impaired metabolism due to deficiency or improper utilization of certain vitamins may alter sebum flow. Specific Gods, drugs or allergens may aggravate oil excess. Steroid hormones influence the development and function of the sebaceous glands. Generally, testosterone or the male type hormones promote both the growth and excessive function of the oil glands, while the estrogens or the female type hormones counteract both these actions. Work with the pituitary and the adrenal cortical hormones shows that these, too may have direct action upon sebaceous glands. The oil-rich, scale-laden scalp furnishes an excellent culture medium for many types of bacteria, some of which may bear causal rela- tionship to the extension of simple dandruff to clinical seborrhea (2). I have found it increasingly difficult dermatologically to separate simple scalp dandruff from the rest of the seborrheic diatheses, so to my mind, antidandruff agents must have therapeutic value. I think that: 1. The seborrheic state, in all its facets, stems from a common cause. 2. Some disturbances of the sebaceous secretion and epithelial kera- tinization are involved. 3. These disturbances may well be of allergic nature. 4. They are always found associated with bacterial and yeast invasion. Furthermore, legally, if not medically, one of these yeast groups, Pityro- spoturn ovale, has been considered a causative agent of infectious dandruff. Accordingly, any product making antidandruff claims must be capable of destroying both these yeasts and certain associated bacteria (Staphylo-