Site variations in susceptibility to SLS

According to the European Society of Contact Dermatitis (ESCD) guidelines on the sodium lauryl sulfate (SLS) exposure test 'the flexor side of forearm skin with cubital fossa and wrist excluded is the preferred study site'. In this study we analysed the exact anatomic region within the suggested test area in respect to the outcome of the SLS exposure test. 3 test areas at the volar forearm were chosen: 'distal' with a 5-cm distance to the wrist, exact 'midvolar' and 'proximal' with a 5-cm distance to the cubital fossa. 25 healthy volunteers were irritated for 24 hr with 1% SLS. Transepidermal water loss (TEWL) measurements were taken before and 1 and 24 hr after removal of Finn Chambers((R)). Median baseline TEWL showed no significant differences in the 3 test sites. However, postexposure TEWL proximal was significantly (P < 0.01) higher than midvolar and distal. The distal volar forearm showed the lowest TEWL 24 h after the irritation. The differences were in comparison to midvolar (P < 0.01) and proximal (P < 0.001) significant. The results show that it is essential to point out the exact position of the test area at the volar forearm in study reports and to randomize the irritation areas at the volar forearm if different treatments are to be compared.