The present trial was designed to evaluate clinical scores (single observer) of sodium lauryl sulphate (SLS)‐induced skin irritation in a group of subjects (n =10) over a 10‐day period along with various skin function parameters. In order to avoid significant variations due to secondary phenomena, the following parameters were recorded with non‐invasive instruments in this order: skin capacitance (Cl; arbitrary units; CM420 Corneometer), transepidermal water loss (TEWL:, g/m2. H: Evaporimeter) and laser Doppler fowmetry (CBFV: cutaneous blood flow values; Periflux. All examinations were performed during water on reclined relaxed subjects present for at least 10 min in a test, room with controlled temperature und relative humidity (to: 19.5–20.70 C and RH: 47.3 60.3%). The analysis of differential data (∂=value at tx‐value before test; 2‐way ANOVA) was made on single parameters as a function of site (volar forearm versus neck) and time (from 24 h after 48‐h occlusion with 5% SLS up to 10 days later). The profile of erythema scores over time differed between neck and forearm, but the ∂CBFV readings with the laser Doppler instrument did not detect significant site‐time interactions. Roughness (blind evaluation with palpating finger) and capacitance readings (∂CI) showed significant differences between sites, but the profile over time was similar in both locations. ∂TEWL did not differ according to anatomical location. The reason (or different erythema scores on neck and forearm might be related to inherent regional variation of optical properties of the skin or to a substantial contribution of SLS‐induced roughness to the readings of erythema. Indeed, such a discrepancy has already been reported with 10% SLS, and a significant dose effect was observed between 5 and 10% SLS. indicating that these observations were not due to a saturation of the skin vascular response quantified as CBFV. Hence, the influence of optical phenomena on clinical scorings might be worth further consideration.
