Seasonal variation of skin resistance to irritants.

In order to investigate a possible seasonal variation in the skin response to irritants, 17 healthy volunteers were patch tested with sodium lauryl sulphate (SLS) and nonanoic acid in the winter and summer. The response to these irritants was quantified by visual scoring, measurement of transepidermal water loss, measurement of electrical conductance indicating the hydration state of the superficial epidermis, measurement of blood flow by laser Doppler and measurement of oedema by ultrasound A-scan. Significantly stronger reactions to SLS were found during the winter than the summer as indicated by visual scoring and by measurements of transepidermal water loss, whereas no significant seasonal variation was found in the response to nonanoic acid. A decreased hydration state of the epidermis of unexposed skin was found during the winter, and we believe this to be responsible for the increased susceptibility to SLS during this season.