Anatomical site differences of sodium lauryl sulfate-induced irritation: randomized controlled trial

Sodium lauryl sulfate (SLS)-induced contact dermatitis is a commonly used model for testing the effects of different topical formulations. According to the guidelines, the volar forearms are the preferred testing site; however, other anatomical locations have been used in previous research, particularly the upper back as the clinically used site for testing different antigens.

To investigate the existence of anatomical variations of the skin response to irritation and its effects on the response to treatment.

Irritation was induced with SLS on symmetrical sites on both forearms and sides of the upper back with additional sites exposed to water as controls. Half of the sites were treated with emollient cream while the other half were left untreated. Irritation was assessed using bioengineering methods and clinical scoring. The trial was registered at ClinicalTrials.gov as NCT03231813.

Upper back skin showed higher reactivity to irritants with stronger barrier disruption (measured by Tewameter^® , 80·2 ± 18·3 vs. 48·0 ± 24·2 g m^-2  h^-1 ), more pronounced erythema (measured by Mexameter^® , 186·5 ± 88·4 vs. 92·1 ± 58·2 arbitrary units) and dryness (measured by Corneometer^® , -28·6 ± 14·5 vs. 2·7 ± 16·9 arbitrary units). Skin recovery rates were also influenced by anatomical location with the upper back showing faster recovery (316·7 ± 223·1 vs. 156·2 ± 198·5). Treatment did not lead to improvement in measured parameters, regardless of anatomical location.

The skin's reaction to irritant and recovery was dependent on anatomical location. The location where testing was conducted should always be reported, as treatments tested across different locations could not be directly compared with each other.