Changes in environmental humidity affect the water-holding property of the stratum corneum and its free amino acid content, and the expression of filaggrin in the epidermis of hairless mice

Background: Seasonal changes affect the condition of skin and may trigger various cutaneous disorders. Objective: To clarify the effects of the environmental humidity on the skin pathology, we studied the effects of the humidity on a water-holding function of the stratum corneum. Methods: We evaluated the skin surface conductance, amino acid in the stratum corneum, and immunoreactivity of filaggrin of the epidermis of hairless mice kept in different environmental humidity. Results: Skin surface conductance in the stratum corneum of hairless mice 3-7 days after transfer from a humid environment ( > 80% relative humidity) to a dry (< 10% relative humidity) environment, was significantly lower than that of the mice transferred from a normal environment (relative humidity = 40-70%) to a dry environment. The free amino acid content in the stratum corneum significantly decreased 24 h after we transferred the mice from a normal to a dry condition, then it recovered to the original level within 3 days, white the mice transferred from a humid to a dry condition showed a significantly tower amino acid content even 7 days after the transfer. No obvious change was observed in the relative composition of the major components of the free amino acids during the experiments. Immunoreactivity of filaggrin, which is the main precursor of free amino acids in the stratum corneum, also became faint in the epidermis of the mice transferred from a humid or normal to a dry environment. Conclusion: These results suggested that a drastic decrease in the environmental humidity reduced the total free amino acid generation and consequently induced skin surface dryness in the stratum corneum. (C) 2002 Japanese Society for Investigative Dermatology. Published by Elsevier Science Ireland Ltd. All rights reserved.