LOSS OF WATER FROM THE STRATUM-CORNEUM INDUCES EPIDERMAL DNA-SYNTHESIS IN HAIRLESS MICE

Many clinical studies have shown that low humidity has a deleterious e ffect on skin, but the mechanisms involved are poorly understood. To c larify the changes that occur in skin, me examined epidermal cell prol iferation in mice kept in a dry (relative humidity < 10%) or a moist ( relative humidity > 90%) environment. In animals exposed to low humidi ty, epidermal DNA synthesis started to increase within 12 h, reaching twice the original level, and the increased level was maintained for u p to 5 days. The transepidermal water loss (TEWL) of mice kept for 12 h in the dry environment was the same as that of mice kept in the mois t enviroment, but the skin conductance was lower. The increase in epid ermal DNA synthesis following exposure to the dry environment was inhi bited by topical application of petrolatum. It is concluded that loss of water from the stratum corneum induces epidermal cell proliferation within 12 h, and this change occurs in the absence of apparent cutane ous barrier dysfunction.