THE ANATOMY AND HISTOLOGY OF AGING SKIN*, By W•RRE•½ A•qI)REw Department of .4natomy The Bowman Gray School of Medicine, l/Fake For:st College, l/Fake Forest, N. C. INTRODUCTION The skin is one of the most conspicuous features of the body of any person or animal. It is so available for visual observation and for palpa- tion that we frequently characterize people in our descriptions by the ap- pearance of the skin. This has been particularly true of age. The con- cept of the rosy and elastic skin of a young person as compared to the pale or yellowed and somewhat flaccid, inelastic skin of the old person, is well known. The skin is a coverin• for the entire body. It is a protective covering which prevents the drying out of the delicate tissues beneath it and which prevents the entrance of injurious organisms. There is a layer of dead cells rather firmly cemented together covering the entire surface of the body. A word of caution, however, should be interposed. The skin it- self is not to be thought of as a dead covering. It is only the superficial cells of one part of the skin, the epidermis, which are dead. The skin itself is an organ with many and important functions. It is not only an organ but it is a complex organ made up of many and varied parts. The two fundamental parts of the skin are the epidermis, a cellular layer, and the dermis, which is composed primarily of connective tissue. Besides these two essential parts, there are the so-called appendages of the skin, thousands of minute glands, including the sweat glands and the oil or seba- ceous glands, generally but not always connected with the roots of the hairs. Then also there are the nails and finally the hairs themselves which are found on almost every part of the body with the exception of the palms of the hands and soles of the feet. The epidermis and the dermis, the two chief subdivisions, again are fairly complicated parts and the epidermis is found to be divided into a number of layers. The first of these layers, the lower layer, is known as * Presented at the May 13, 1955, Meeting, New York City. t These studies were aided by a contract between the Office of Naval Research, Depart- ment of the Navy, and the Bowman Gray School of Medicine. NR 102 024. 299

300 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS the stratum germinativum, or "germinative" layer, because it is here that the cells are definitely living and dividing to form new cells. The second layer is known as the stratum granulosum. Here the cells are entering upon a moribund condition and there are large granules present which stain deeply with basic dyes. The third layer, above the stratum granulosum, is usually called the stratum corneum. It is composed of dead cells which contain a very large amount of a horny or hard substance known as keratin. It is this outermost layer which is continually "scuffing off" and being lost to the body. The dermis, besides containing the roots of the hairs, the ducts of the glands and portions of the glands themselves, has in it the rich blood supply and the lymphatics of the skin as well as many nerves and end organs for the reception of sensations of pain, pressure, touch and of temperature. EARLIER WORK ON Aoz CH.•NOv. S IN THE SKIN As early as 1896 Unna described changes in the fibers in the dermis. These fibers are of two main types, white or collagenous and yellow or elastic. Unna found changes in both types. The collagenous fibers under- went a change toward the basophilic type rather than the eosinophilic type of staining and the elastic fibers often became swollen and fragmented. The elastic fibers seem to undergo a modification into a material which Unna called "elacin." Unna believed that the collagenous and elastic fibers even merge together in some cases in old age. Writers have differed on what happens to the fibers in the dermis in senility. Strobel (23), for example, found that the principal age change was in the white fibers and that from the time of the middle thirties on these fibers showed an atrophy and a rarefaction. He does not believe that the elastic fibers show any truly degenerative change with age but only a cer- tain extension in length, probably the effect of overstretching. His study represents an extensive series of cases as he had specimens of unexposed skin taken from the umbilical region, from the internal aspect of the thigh and from the upper arm of two hundred and forty individuals belonging to all age groups. Hill and Montgomery (14) studied human skin from 20 autopsies, includ- ing four senile subjects ranging from sixty-one to seventy-eight years of age. They studied the pubis, the axilla, the chest, the scalp and the web of the toes. They say that the changes both in the collagenous and the elastic fibers are not very marked. They state that while the collagenous fibers seem to be atrophic in some of the very old persons the presence of clumped masses of elastic tissue does not seem particularly related to age and that the elastic connective tissue about the hair follicles and their sheaths and just beneath the epidermis seem to be well preserved even in old people. They believe that findings by others concerning the changes in the elastic