Irritant patch testing with sodium lauryl sulphate: interrelation between concentration and exposure time

BACKGROUND: It is well known that the degree of skin reaction to an irritant depends on its concentration and exposure time. OBJECTIVES: To determine the interrelationship between the concentration of sodium lauryl sulphate (SLS) and exposure time in both weak (subclinical) and severe reactions. METHODS: Patch testing with SLS was performed at different concentrations (0.125%, 0.25%, 0.5%, 1.0% and 2.0%) and with different exposure times (3, 6, 12, 24 and 48 h). Evaluation was conducted by measurement of transepidermal water loss and by laser-Doppler flowmetry both 30 min and 24 h after patch removal. RESULTS: We found more reliable and constant skin reactions 24 h after patch removal, and a higher correlation between SLS concentration and skin reaction. CONCLUSIONS: We conclude that the concentration of SLS influences the test outcome to a larger degree than the exposure time. We present formulae by which the outcome of SLS patch testing at various SLS concentrations ranging from 0.125% to 2% and any exposure time between 3 and 24 h can be estimated.