380 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Although the rise in water content of old skin is far from spectacular, the data appear to be sufficiently confirmed (13-15) to merit some considera- tion. The somewhat higher water content h/rs been explained on the ground that the physico-chemical changes in old collagenous and elastic fibers affect their water-binding ability (15). While this explanation may well be correct, it is not supported by experimental evidence, although it would be easy to obtain such evidence by direct experiments. Indirect evidence for a decreased water-binding capacity of old skin has been advanced by Herrmann (20). In carefully controlled studies, he pointed out that water is more loosely bound to the aging tissue colloids and released more easily thus the false impression is created that old skin has an increased water content. The most impressive and characteristic chemical changes in senile skin occur in the coriurn. The exact nature of these changes is unknown, but there is ample evidence for their existence. Thus young collagen is trypsin- resistant, but aging collagen is digested by trypsin (16). The tinctorial properties of the corium are also markedly changed. There is an increase in elastic staining of the corium which gave rise to the belief that the elastic fibers actually become more numerous with advancing age. Also a "merg- ing" of the collagenous fibers with the elastic tissue has been described. The term "senile elastosis" to denote these changes (17) is anachronistic and should be abandoned. It is based on two fallacies common with his- rochemists: the first fallacy is that if two objects look alike or stain alike, they have the same composition. By this reasoning, faraway mountains and the blue sky should be identical. The other misconception stems from the belief that if two objects are next to each other, they originate from each other, as though the sky were a product of the blue mountains. Today we know that the apparent increase of elastic tissue is due to a degeneration of the collagenousfibers. In the course of this degeneration, the collagenous fibers become susceptible to elastic stains, assume abnor- mal shapes and finally disintegrate into amorphous masses which are vulner- able to trypsin. The changed tinctorial properties of the collagenous fibers indicate profound changes in their composition, but pertinent chemical data are not available. Whether or not the recently described histochemi- cal changes in the so-called basophilic collagen (18) are applicable to senile collagen, remains the subject of further studies. Equally serious are the morphological and chemical changes in the aging elastic fibers, both at the junction of the epidermis and dermis (12, 19) and in the deeper layers (12, 15). Again, the marked staining abnormalities of the old elastic fibers reflect their changed chemical composition the exact nature of this change is unknown. In elastic fibers of other old tissues an accumulation of calcium and an increase of dicarboxylic amino acids has been reported (12).

THE CHEMISTRY OF THE AGING SKIN 381 The ground substance apparently becomes less permeable in old age, as evidenced by its cloudy and opaque appearance. The spreading reaction is decreased in old animals (12). Again the chemical basis of these changes is unknown. The paucity of chemical information about the components of aging skin leads to two conclusions: 1. In view of the unexplored chemical characteristics of the aging skin, there is no rational dermatological therapy or cosmetic device for the "re- juvenation" of aging skin. At best, all recommended local treatments (hormones, vitamins, etc.) are based on alleged morphological changes and "improvements" which have been subjectively evaluated. In the author's opinion, the only acceptable cosmetic measure for the treatment of old skin is the replacement of the fatty cover of the skin surface by frequent lubrication with ointments or lotions. The fatty cover helps in retaining the moisture in the horny layer and prevents the chapping and drying of the skin surface. 2. There is a great need for further chemical analyses of the components of the aging skin. It is indispensable to have objective data on the cutane- ous changes of the aging process. In the absence of such data, we cannot devise adequate cosmetic measures for "resuscitating" old skin. SUMMARY' In senile skin the following chemical changes have been described: 1. Dryness of the horny layer with possible changes in the process of keratinization. 2. An increased calcium, magnesium and ash content of whole skin. 3. Profound alterations in the collagenous and elastic fibers and in the ground substance of the corium. The exact chemical nature of these changes is unknown. It is emphasized that there is a great need for further chemical studies in this field in order to develop rational cosmetic measures for the treatment of aging skin. REFERENCES (1) Rothman, S., "Physiology and Biochemistry of the Skin," Chicago, University of Chi- cago Press (1954), p. 380. (2) Lewis, B. L., and Montgomery, H., "The Senile Nail," 7. Investigative DermatoL, 24, 11 (1955). (3) Tadokoro, T., and Ugami, H., "On the Cystine and Cysteine Contents of Human Hair," 7. Biochem., 12, 187 (1930). (4) Brown, H., "The Mineral Content of Human Skin," •e. Biol. Chem., 75, 789 (1927). (5) Biirger, M., "Haut- und Stoffwechsel," alrch. Dermatol. u. Syphilis, 191, 71 (1950). (6) Meyer, A., "Vergleichende Gesamtsterin- und Sterinesterbestimmungen der Haut des wachsenden und erwachsenen Organismus," Z. Kinderheilk., 50, 596 (1931). (7) Brown, H., "The Mineral Content of Human, Dog and Rabbit Skin," 7. Biol. Chem., 68, 729 (1926). (8) Herrmann, F., "Erweiterung des Verfahrens der Schnittveraschung. Differenzierung der anorganischen Struktur gesunder und kranker Haut," Z. wiss. Mikroskop., 52, 257 (1935).