The efficacy of skin barrier protecting products is commonly assessed using pre-treatment models combined with standardized irritant challenges. However, the influence of application frequency prior to irritation is rarely addressed systematically. The objective of this study was to apply an intra-individual, dose- and frequency-dependent pre-treatment design on the forearm to evaluate the protective effect of a wound-protection cream on exposure to 0.5 % sodium dodecyl sulfate (SDS) compared to untreated skin.
Four test sites were allocated across the volar forearms of 29 healthy female volunteers with dry skin: one untreated control site and three sites pre-treated with the test product according to different application frequencies (once, twice, or three times) within 24 hours prior to irritation challenge. Product applications were scheduled immediately after baseline assessment/measurement (Day 0), on the evening of Day 0, and 2 hours before the next assessment/measurement at Day 1. Skin barrier function and irritation were assessed by transepidermal water loss (TEWL) and visual erythema scoring at baseline 1 (t0), 2 hours after the last application before SDS exposure (baseline 2/t1), and 24 hours after removal of a 0.5 % SDS patch (t2). Values at t1 and t2 were computed relative to baseline (t0). Additionally, t2 relative to t1 was analyzed to isolate the post-irritant effect from the acute pre-SDS product effect.
24 hours after irritation, all pre-treated sites showed statistically significantly lower TEWL values and erythema scores compared to the untreated control, indicating a significant protective effect of the test product, already evident after a single application.
This dose-frequency pre-treatment forearm model represents a robust and reproducible approach to investigating skin barrier protection under acute irritant exposure. Beyond demonstrating efficacy, the design allows differentiation of application-dependent protective effects, supporting relevance for claim substantiation and product recommendations.