Dry environment increases mast cell number and histamine content in dermis in hairless mice

Background A variety of skin diseases, such as atopic dermatitis, senile xerosis or psoriasis tends to worsen during the dry winter season. These skin diseases are also characterized by itch sensation. Objectives To evaluate the generation of histamine in the dermis of hairless mice kept under various conditions of environmental humidity. Materials and methods We carried out the quantification of mast cell population and evaluated the histamine content in the epidermis, dermis and serum of the mice kept under various conditions of environmental humidity. Results Histamine content in the dermis of the mice kept in a low environmental humidity (relative humidity < 10%) for 3 and 5 days was significantly higher than that of the mice kept in a high environmental humidity ( relative humidity > 80%) for the same period of time. No significant difference was observed on the histamine content in the epidermis between the two humidity groups. The number of mast cells in the dermis of the mice kept in the low environmental humidity was significantly higher than that of the mice kept in the high environmental humidity. Topical application of petrolatum reduced the level of histamine in the dermis of the mice under the low environmental humidity. Conclusions These results suggest that a low environmental humidity increases mast cell number and dermal histamine content.