Human cutaneous irritation: induced hyporeactivity

The variation in human skin response to sodium lauryl sulfate (SLS) was determined with patch and open applications. Reactions in different subjects and in multiple simultaneous patch tests were compared. Skin responses were assessed with visual scoring (VS), laser Doppler velocimetry (LDV) and transepidermal water loss (TEWL). Previous open, unpatched SLS exposure decreased patch test reactivity to 1% SLS assessed with VS (p less than 0.05) or LDV (p less than 0.05). Corresponding TEWL alteration was inconstant. Variation in reactivity at different test sites in multiple simultaneous tests was considerable, though less than the variation at different test times (p less than 0.05). Inter-subject variation in test reactivity was greater than the variation between different test times or adjacent test sites. Repeated open applications and the subclinical dermatitis appear to have produced a hyporeactive state. The results suggest that non-specific skin inflammation is elicited by multiple factors, e.g., stratum corneum integrity and vascular reactivity. Their balance determines the ensuing reactions. The induced hyporeactivity may be one of many causes of false negative diagnostic patch tests.