Skin irritancy from nonanoic acid

100 hospitalized patients with skin disease were patch tested with graded dilutions of nonanoic acid (NON), sodium lauryl sulfate (SLS) and benzalkonium chloride (BENZ). Smooth dose-response curves were obtained. The concentration needed to produce a discernible irritant reaction in 50% of the population (ID50) was found to be lower in cases of irritant than of allergic contact dermatitis; this finding warrants further study. Björnberg's observation that it is not possible to predict the strength of the reaction to one irritant by knowing the strength of the reaction to another was confirmed. Benzalkonium chloride caused a high frequency of pustular and/or bullous reactions with scarring as a sequela. It is suggested that this irritant could be replaced by nonanoic acid in experimental studies of topical irritancy, since the test reactions from nonanoic acid were reproducible, easy to read and left no staining or scarring.