WATER AND THE HORNY LAYER 71 1.0 (Wma x -W) 0.1 (mg H20/m e S.C.) o.o• I i I I 0 100 200 300 400 Figure 3. Plot of In (Wmax- W) VS. t 1/2. Hydration data is same as in Fig. 2. Trypsin- harvested 8 mm punch of SC from male caucasian, age 45 years, hydrated at 97 per cent RH, 30 ø C to Wm•x equals 0.90 mg H,/mg SC approximately 0.11 mg H20/mg SC versus 0.06 mg H20/mg SC at 20øC. The sample has enough water to be pliable at 30øC, but less than the necessary 0.10 to 0.15 mg H20/mg SC (1) to be pliable at 20øC. At higher RH, when secondary bound water is present, the temperature effect is reduced, pos- sibly due to the rapid interchange between the secondary water and the pri- mary bound water necessary for pliability. In addition, Middleton and Allen (13) indicated that reduced temperature causes a reduction in the extensi- bility of SC exclusive of water content. The effects of temperature on both water content and extensibility indicate that temperature should be con- sidered as one factor in the increased incidence of dry skin (2) observed in cold dry weather. (Received June 11, 1975) REFERENCES (1) I. Blank, Factors which infiuepcc the water content of the stratum corneum, J. In- vest. Dermatol., 18, 433-40 (1952). (2) L. Gaul and G. B. Underwood, Relation of dew point and barometric pressure to chapping of normal skin, J. Invest. Dermatol., 19, 9-19 (1952). (3) T. S. Spencer, C. E. Linamen, W. A. Akers, and H. E. Jones, Temperature de- pendence of water content of stratum corncure, Brit. J. Dermatol., 92, 159-6d (1975). (d) A. M. Kligman and E. Christophers, Preparation of isolated sheets of human stratum corncure, Arch. Dermatol., 88, 702 (1963).

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