Delayed time course of irritation by sodium lauryl sulfate: observations on threshold reactions.

Irritant reactions to sodium lauryl sulfate were induced on the backs of 20 volunteers by means of patch test occlusion for 24 h. Different concentrations ranging from 0.25% to 2% were used, the lowest concentration being borderline irritant. The skin tests were read at 24, 48 and 72 h. Both the % of responding individuals and the intensity of the skin reactions were maximal at 48 h for all test concentrations. It is concluded that irritants may provoke inflammatory reactions which are not completely developed after 24 h, and are thus very similar to allergic patch test reactions.