THE PARTICULARITY OF HUMAN SKIN WILLIAM MONTAGNA ALL MEDIA of communication warn us constantly that natural skin can be ugly and evil, and that to be civilized we must combat its natural attributes. Overly aware of the impression we make, we bathe our skin daily, we accentuate or depress its color with various artifices, we try to make it smoother, we attempt to depress the growth of hairs in some areas and to induce it in others. We wage a constant war against the natural odors from the secretion of skin glands. Yet, skin goes on unconcernedly, ignoring, tolerating or trying to overcome the ravages of these harassments. Man has survived because his skin is undaunted by countless centuries of iniquity, and has lost none of its sturdiness, and may even have gained some. In spite of all the pamperings, skin ages, as do all other organs. It loses tonus, it loses its youthful bloom and smoothness the scalp of some men undergoes curious involutional changes, and may become bald some women develop variable amounts of hirsutism. Wattles and dewlap form on the face and throat, and sun-baked cracked-clay patterns form on the back of the neck. Claims that the application of certain youth-restoring lotions can change this inexorable, genetically determined devastation are less than honest. We live in an unfriendly society, and we should use every conceivable device to make ourselves more acceptable the use of makeup can make us appear more attractive and younger, but we should not be hoodwinked into believing that we are restoring vigor and youth- fulness to our tired skin. The two main component parts of skin, dermis and epidermis, are each derived from a different germ layer. The epidermis and its appendages, being on the surface, have drawn, and will always draw, our greatest attention. Yet, the various expressions of the epidermal structures seem to be triggered and controlled by agents in the dermis. Since the dermis seems to be morphologically uninteresting, the biologist has cleverly avoided studying it now, he can no longer ignore it, because electron microscopists, biochemists, tissue culturists and experimental embryolo- gists are finding out that the dermis is far fi'om dull, and together, they will gradually squeeze its secrets out of it. When we understand the various evocating potencies of the dermis, we will begin to find intelligible 303

304 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS the many vicissitudes of the epidermis, and not before. We do not even know what agencies govern the differentiation of cutaneous appendages from the simple, undifferentiated epidermis during the early epochs of organogenesis. The early pattern of differentiation of cutaneous append- ages is orderly and precise. The hair follicles grow. first, and from them grow their secondary appendages, the sebaceous glands and apocrine sweat glands. The eccrine sweat glands develop last, their topographic distribution often determined by the distribution of the hair follicles. Each of these appendages differentiates into an organ that produces a different end-product. The surface epidermis is concerned with manu- facturing keratin, a mantle of dead cells that protects the body the hair follicles produce cylinders of keratin of varying thickness, length and color. Other than being ornamental, pelage serves little purpose in modern man. Sebaceous glands secrete on the surface of the skin oily, waxy substances that keep the corneal mantle supple. Eccrine sweat glands, the thermoregulatory organs of the body, are structurally and functionally beautiful organs that must be indefatigable in eliminating sweat. Apo- crine sweat glands, in spite of their exuberant development, in the axilla of man, secrete a small amount of substance, which when degraded by bacteria becomes fetid, a function of little use in modern man. These glands develop slowly during infancy, attain some activity in late child- hood and blossom just before adolescence. Regardless of what usefulness we can ascribe to apocrine glands, it is incorrect to consider them vestigial organs in man, since in no other mammal are they as well developed as they are in the human axilla, around the nipple of the breast and in the external auditory meatus. Skin shows striking topographic differences over the body. It is rough in some places, smooth in others it is taut or lax, highly colored or pale it is naked or hairy, and thick or thin. Skin is always thicker on the dorsal than on the ventral part of the body, and it is thicker on the ex- tensor than on the flexor side of the limbs. Satisfy yourselves of this by pinching first the skin on the lateral side of your forearm and then the skin on the roedial face of it. Differences in thickness, in tautness, in color, in smoothness and in the number of hairs and glands present are accompanied by differences in the quantity and quality of the connective tissue ele- ments present in the dermis, and most important, by the pattern and the richness of the blood-vascular system. An extensive study is now being carried out in our laboratory by Doctors Richard A. Ellis and Giuseppe Moretti on the differences in vascularity of the skin over the different regions of the body, and the results obtained thus far emphasize the enor- mous differences that occur. When the catalogue of the surface blood vessels of the skin is completed, we will have a better understanding of the gross and the minute topographic differences that exist in the skin.