Clinical morphology of sodium lauryl sulfate (SLS) and nonanoic acid (NAA)irritant patch test reactions at 48 h and 96 h in 152 subjects

In this study of 152 women, comparison of patch test responses between 2 ir ritants over 96 h. at 2 symmetrical anatomical sites is studied. 2 irritant s, each at 4 different concentrations (nonanoic acid (NAA) 80%, 40%, 20%, 1 0%; sodium lauryl sulfate (SLS) 3%, 2%, 1% and 0.5%) and using propan-1ol a nd 'water for injection' as the respective controls, were placed as 15 mu l aliquots, soaked onto filler paper discs in Finn Chambers, on the voluntee r's left and right lower back. The patches were removed at 47, and read at 48 and 96 h. Irritant reactions were evaluated for erythema and surface cha nges by degree and area affected. Statistical analysis of the results showe d that erythema decreased with time for all concentrations of NAA, and at h igher concentrations for SLS. Surface changes increased with time for SLS a nd at higher concentrations of NAA. There was no statistically significant difference comparing left and right sides. Traditionally in patch testing, reactions which fade after 48 h have been regarded as irritant rather than allergic. This study refutes that assumption. Data from our left to right c omparisons, made in the same individuals at the same time, show that irrita nt reactions may be more reproducible than previously appreciated.