ALTERATIONS IN THE SKIN PHYSIOLOGY $ 3. Keratin reducers. 4. Keratin stimulators. 5. Protein precipitators. 6. Desiccators. 7. Oxidizers. 8. Hydrolyzers. Though we cannot readily apply all of these effects to the problem of de- tergency, certain of them, such as fat solvency, sweat neutralization, and keratin alteration, have long been associated with the cutaneous action of soaps and detergents. We know that solvents, soaps, and synthetic detergents are able to dis- solve or emulsify lipids and thereby remove them from the skin. The natural lipid material, known as sebum, is a secretory product of the sebaceous glands which is extruded through the hair follicle orifices to form a thin waxy film upon the skin surface. According to Rothman, the protec- tive action of this lipid film against water and water-soluble materials is one of hindering the wetting and penetration of the horny layer. He be- lieves, however, that this role has been overemphasized and that the film is not the only factor which protects the skin against water and water-soluble materials. It has long been held that whenever the skin became dry, or roughened, or cracked, it did so because the lipid content had in some way been dimin- ished. There seems to be no question that the defatted skin surface is more dried and roughened than the normally fatted surface, but the exact role of sebum in maintaining the soft, pliable condition of the skin is not com- pletely understood. It is possible that the layer of sebum may definitely assist in providing a feeling of smoothness, but the recent work of Irvin Blank has introduced a new concept regarding skin pliability. Blank found that the water content of keratin is far more significant in maintaining its pliability than the action of fats and oils. By using cornified epithelium (dried brittle callus from the plantar surface of the foot), and allowing it to remain in contact with lanolin, petrolatum, and natural glycerides of fatty acids lot months at normal or elevated temperatures, he noted that the callus repeatedly failed to soften. However, when the dried brittle callus, under the same conditions, was allowed to absorb a little moisture, it soon became sott and pliable. Further, by taking skin and removing the surface lipids, as described by Winson and Burch, he was able to corroborate their finding that the re- moval of the surface lipid did not increase the rate of water loss from the specimen. This served to indicate that there is no lipid layer acting as a barrier to water loss. On the other hand, when the skin is thoroughly ex- tracted with an ether-alcohol mixture for five days and then allowed to ab-

6 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS sorb water, its rate of water loss is 20 to 50 times greater than seen in the un- extracted skin. This procedure would indicate that the extraction process had created an alteration in barrier effect more significant in influenc- ing water loss than was observed after simply removing the surface lipid layer. He concluded, therefore, that the lipid barrier on the skin surface was not the factor which inhibited watec diffusion from the skin and that the true barrier was contained somewhere within the epidermis, probably at the base of, or below, the horny layer. Applying the knowledge of loss of water by evaporation from the skin surface, Blank found that meteorologic conditions, such as relative humid- ity, temperatures, and air currents, have a great influence upon the water content of keratin and thus tend in no small degree to regulate its softness and pliability. He reported that "under the low relative humidity of winter weather and heated houses or the rapidly flowing air of windy conditions, the stratum comeurn does dry out and the fissures of a chapped skin and scaling of a windburn can develop because of the brittleness of a dried stratum corneum." This laboratory observation concerning the pliability of keratin has a striking clinical corollary in the studies by Gaul and Underwood, who re- ported the relationship of dewpoint and barometric pressures to chapping of normal skin. In a series of clinical observations of a group of patients, they plotted the incidence of hand chapping against air humidity and barometric pressure. Their observations showed that dryness, scaling, and cracking of the skin were accentuated when the air humidity (dewpoint) experienced a sudden drop. Further, they noted that the exacerbations were preceded by low barometric pressures followed by sudden rises parallel- ing the onset of the chapping. The authors found it difficult to show that soap alone accentuated the chapping however, they stated that washing and cleaning days definitely aggravated the chapping condition. The use of very hot water and soap seemed to have more influence on the degree of chapping than did the use of cool water and soap. These studies, and others, dealing with water content of keratin, its pliability, brittleness, scaling, and fissuring, have an intriguing implication in the detergent effects upon the skin. It is well established that the clinical appearance of the skin following the excessive use of detergents is quite similar to that noted in the chapping phenomenon. It is also a fact that detergent dermatitis is more common during the cold months of the year. When seen during the warm months, however, the dermatitis is generally a result of excessive use of detergents, habitual lack of rinsing them from the hands, failure to dry the hands, or an innately dry skin asso- ciated with subnormal fat secretion. Loss of water from keratin may well explain the dryness, scaling, and redness which reflects the cutaneous action of detergents. Although the sebaceous barrier may play no part in inhibit-