194 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS -0.75 GLU PC^ -0.46 HIS uc^ -0.31 -0.54 ARG = ORN CIT -0.75 ASP ALA Figure 8. Correlation coefficients showing the inverse relationships between levels of free amino acids and their metabolites in cheek skin of 46 female subjects. acceleration of keratinization. A similar tendency was observed when hexadecane and ultraviolet rays as well as LAS were applied. In addition, the rates fell further as the irradiation with ultraviolet rays was prolonged (9). These suggest that the conversion rates well reflect the degree of hyperkeratosis. The decreases in the rate of conversion may be attributed to a decrease in activity of enzymes which catalyze the conversion or a scarcity of time for relevant metabolism due to acceleration of the turnover. The precise mechanism, however, remains as yet to be elucidated. In hyperkeratotic epi- dermis, at least, free amino acids in the stratum corneum are affected, and the rates of amino acid conversion through the four metabolic pathways involved in the keratini- zation especially reflect this feature of keratinization. Taking advantage of the process, the skin condition could biochemically be estimated with water soluble constituents extracted from the skin surface without invasion. Dry skin in winter. Each of the four amino acid conversion rates measured in dry skin was lower than those in normal skin (p 0.05), as shown in Figure 7. This suggests that keratinization was disordered simultaneously with the skin's getting chapped. Para- keratotic changes in the epidermis can be examined by usual histological techniques. It is, however, difficult to perform biopsies on many subjects. A new technique reported recently provides a simple method of estimating parakeratotic changes, wherein residual nuclei in the stratum corneum are counted in a cornified cell specimen detached with the aid of adhesive tape (10, 11). In the investigation of parakeratotic changes, the residual nuclei were evaluated by the new procedure. The results are shown in Table V. In normal keratinization, the nuclei disappear in the process of differentiation, and the stratum corneum consists of non-nucleated cells alone. When the keratinization is disturbed, the disappearance becomes incomplete, resulting in nucleated cells in the stratum corneum. Although all the subjects chosen for the present study were healthy, only 19.5% showed stratum corneum consisting of non-nucleated cells alone. Accord- ingly the nucleated horny cells were found in a considerable portion of the subjects. The degree of parakeratosis was proportional to the roughness of the skin. As described above, the studies on changes in the composition of free amino acids in the stratum corneum and the extent of parakeratosis suggest changes in the epidermis in association with skin roughness and that skin lesions associated with dry skin do not stay within the stratum corneum. In experimentally induced hyperkeratosis, the skin surface ex- hibited changes similar to the surface of dry skin: the surface became dry, furrows and

AMINO ACID METABOLITES IN DRY SKIN 195 ridges were indistinct, and scales were visible. These facts suggest that the etiology of the superficial lesion of dry skin may partly be interpreted as the stimulatory effects of low temperature and dry air in winter. These cause a slight inflammation of the skin, accelerating keratinization, leading to abnormal stratum corneum. Dry skin encountered in winter may involve only the surface of the stratum corneum without changes in viable epidermal levels. Although it is also certain in the present study that parakeratosis could not be demonstrated in some cases in which roughness of the skin was macroscopically evident, examination with an increasing number of panels revealed changes in free amino acid compositions similar to those noted in hyperkeratotic epidermis. In addition, parakeratosis was increasingly noted in dry skin. All of these results suggest that changes in the epidermis take place in dry skin. Based upon this assumption, in order to obtain a good treatment for chapped skin, it is necessary to consider improvement of the lesion in the viable epidermis. REFERENCES (1) P. Flesh, C. Hodgson, and E. C. J. Esoda, Water-soluble organic components of psoriatic scales, Arch. Dermatol., 85, 84-92 (1962). (2) E. Schwarz, Freie aminosauren und hornstoff in psoriatischen und normalen epidermalen verhor- nungsprodukten, Arch. Klin. Exp. Dermatol. 225, 229-305 (1966). (3) S. Marstein, E. Jellurn, and L. Eldjarn, Reduced amounts ofpyroglutamic acid in scales from psoriatic plaque, Arch. Dermatol., 108, 578-579 (1973). (4) J. D. Rossmoller and W. G. Hoekstra, Hexadecane-induced hyperkeratinization of guinea pig skin. IV. A comparison of free amino acid levels in normal and hyperkeratotic epidermis, J. Invest. Der- matol., 47, 44-48 (1966). (5) K. Nakamura, Y. Morikawa, and I. Matsumoto, High speed liquid chromatographic analysis of citric, lactic, urocanic and pyroglutamic acids in cosmetic products, Bumeki Kagaku, 29, 314-318 (1980). (6) I. Horii, S. Akiu, K. Okazaki, K. Nakajima, and S. Ohta, Biochemical and histological studies on the stratum corneum of hyperkeratotic epidermis, J. Soc. Cosmet. Chem. Japan, 14, 174-178 (1980). (7) I. Horii, K. Kawasaki, J. Koyama, Y. Nakayama, K. Nakajima, K. Okazaki, and M. Seiji, His- tidine-rich protein as a possible origin of free amino acids of stratum corneum, J. Dermatol., 10, 25-33 (1983). (8) N. W. DeLapp and D. K. Dieckman, Biosynthesis of pyrrolidone carboxyric acid in hairless mouse epidermis, J. Invest. Dermatol., 68, 293-298 (1977). (9) Unpublished observations. (10) H. Goldschmid and A.M. Kligman, Exfoliative cytology of human horny layer, Arch. Derm., 96, 572-576 (1967). (11) H. Goldschmid and M. A. Thew, Exfoliative cytology of psoriasis and other common dermatoses, Arch. Derm., 106, 476-483 (1972).