The chronic effects of the irritant sodium lauryl sulphate (SLS) on stratum corneum (SC) barrier function, determined by transepidermal water loss (TEWL) measurements and on epidermal cell kinetics, estimated by stratum corneum turnover time (SCTT) determination (dansyl chloride staining method), were investigated in 18 healthy female volunteers. SLS (7·5%) was applied without occlusion for 20 min once daily, over a period of 3 weeks (5 days a week) on dansyl chloride-stained skin and on untreated skin. SCTT of untreated skin (19·3 ± 0·8 days; mean ± SEM) was not changed by daily treatment with water (control) (19·3±2.0) but was significantly reduced by SLS (10·9±0·6; P0·0001; compared to controls). However, TEWL was increased in SLS-treated sites 1·5-fold after 4 days of treatment (5·3±0·6 vs. 3·5 ± 0·3; P<0·001). At the end of the second week, TEWL was increased 2.6-fold and after 3 weeks TEWL was 3·3 times higher than in controls (13·0±1·6 vs. 3·9, P0.0001) The intensity of SLS-induced irritation as measured by TEWL was significantly correlated with baseline TEWL (r=0·50; P0·02) and significantly negatively correlated with SCTT of SLS treated sites (r=− 50; P0·02) but not with SCTT of untreated skin (r=0·19).