Despite the frequency of irritant contact dermatitis, very little is known about the duration of barrier function impairment following cumulative irritant contact dermatitis. We studied post-irritation irritant reactivity by assessing the response to SLS irritation in previously irritated sites. Cumulative irritant contact dermatitis was induced on the forearms of 15 volunteers aged 18 to 50 years by repeated occluded application of 0.5% SLS 1 h per day over 3 weeks. 3, 6 and 9 weeks later, previously irritated and unirritated control sites were challenged with 2% SLS under occlusion for 23 h. Irritation was assessed by visual scoring, transepidermal water loss (TEWL) as an indicator of epidermal barrier function, and capacitance as a parameter of epidermal water content. While no difference in irritant reactivity between pre-irritated and unirritated sites was observed 3 weeks following irritant contact dermatitis, there was a significant hyporeactivity of previously irritated skin as expressed by clinical scores, TEWL and capacitance at 6 and 9 weeks. Our results indicate that epidermal barrier function remains altered even 9 weeks after cumulative irritant contact dermatitis. With regard to patch testing, post-irritation hyporeactivity might be a cause of false-negative tests on previously irritated sites.