Sodium lauryl sulfate irritant patch tests: degree of inflammation at various times.

Irritant reactions were induced on the forearms of 10 normal subjects with 10% aqueous sodium lauryl sulfate under patch test occlusion for 24 h. Test sites were observed at 24, 26, 28, 30, 48, 72 and 96 h and the degree of inflammation recorded. Inflammation was most prominent at 28 h and decreased in intensity over the time course of the study. Inflammation at 48 and 72 h was similar to when patches were removed. This suggests that inflammatory responses in skin for at least certain irritants like sodium lauryl sulfate do slowly decrease in intensity after 48 h. However, the inflammatory response may initially accelerate after patch test removal and remain intense for at least 48 h. Fading of irritant reactions by 48 or 72 h may not reliably distinguish irritant from allergic patch test reactions. This does not refute the usefulness of a delayed (96 h) reading since inflammation from sodium lauryl sulfate had decreased significantly by this time.