Anatomical Site Differences of Sodium Laurylsulphate Induced Irritation: Randomised controlled trial D Leskur1, J Bukić1, A Petrić1,2, L Zekan1,2, D Rušić1, A Šešelja Perišin1, I Petrić1,2, M Stipić1, N Puizina-Ivić3, D Modun1 1Department of Pharmacy, University of Split School of Medicine, Šoltanska 2, 21000 Split, Croatia 2Split-Dalmatia County Pharmacy, Kneza Ljudevita Posavskog 12 b, 21000 Split, Croatia 3Department of Dermatovenerology, University of Split School of Medicine, Šoltanska 2, 21000 Split, Croatia British Journal of Dermatology. DOI: 10.111/bjd.17633

Lead researcher

Introduction (1) What’s already known? Sodium laurylsulphate (SLS) is commonly used to induce skin irritation. The skin’s susceptibility to irritation could be dependent on anatomical location.

Introduction (2) What’s already known? Anatomical differences in skin response to irritation has been observed in other irritation models such as tape stripping and benzalkonium chloride models. Such differences are also possible in an SLS irritation model, as some studies with limited sample sizes suggested.

Objective The primary aim of the study was to investigate anatomical variations in skin response to irritation and its effects on treatment in an SLS-induced irritant contact dermatitis. The secondary aim of the study was to test the effectiveness of an emollient in the SLS-induced irritation model.

Methods (1) 25 young and healthy participants with written consent recruited Median age: 22.0 years (Interquartile range: 22.0 - 23.5 years) 14 females Baseline skin parameters measured Instrumental (transepidermal water loss, erythema, hydration); and Clinical scoring Instrumentation used – Tewameter, Corneometer, Mexameter (Courage+Khazaka, Cologne, Germany)

Methods (2) Irritation induction: Forearms and upper back Exact sites where irritation was induced were decided randomly for each participant. 60 μL 2% w/v SLS solution under occlusion (12 mm Finn chambers) for 24 hours AND sham irritation: 60 μL water. Irritation and recovery assessment: Instrumentation and clinical scoring Fig.1. Test sites

Methods (3) Treatment: Commercially available emollient cream. Chosen as a treatment based on its ingredients with previously shown positive effects. One forearm and one side of the back treated with the emollient, while the other side was left untreated. Second randomization to determine effects on the treated and untreated sites. Fig.2. Trial timeline

Results (1) Significantly stronger reaction on the upper back in comparison to the forearms. Skin recovery rates (calculated from TEWL change over time) were also influenced by anatomical location with the upper back showing faster recovery. Tested emollient did not lead to improvement of measured parameters in used model or intact skin.

Results (2) Fig.3. TEWL and (b) were irritated with SLS; (b) and (d) were treated with emollient; All data given as mean and SD, unless stated otherwise

Results (3) Fig.4. Erythema – difference from baseline and (b) were irritated with SLS; (b) and (d) were treated with emollient; All data given as mean and SD, unless stated otherwise

Results (4) Fig.5. Hydration – difference from baseline and (b) were irritated with SLS; (b) and (d) were treated with emollient

Results (5) Fig. 6. Barrier recovery rates and derived parameters (a) AUC (b) AUC/TEWL(irritation)# (c) AUC/(TEWL(9th day)/TEWL(baseline)) * Significant difference between barrier recovery rates.Results are given as median± interquartile range. # Data multiplied by 100 to be up-to-scale and shown on the same chart for more clarity.

Discussion (1) Proposed reasons for differences in skin reactivity and recovery Morphological differences of the skin on different anatomical locations. Variations in stratum corneum ceramides and natural moisturizing factor (NMF) constituents. Differences in SLS skin permeability. Baseline skin values of cytokines IL-1RA and IL-8.

Discussion (2) Baseline erythema and hydration values were significantly different between forearms and upper back. TEWL values between anatomical locations were comparable. TEWL was suggested as an irritation predictor Higher baseline TEWL means stronger reaction to the irritant.

Discussion (3) TEWL did not accurately predict a reaction in the present study. Skin properties and susceptibility to irritation dependent on anatomical location. Different skin sites - varied responses to treatment.

Discussion (4) Most conducted studies tested the efficacy on forearms Possible that the achieved effects could not be replicated on other locations. Moreover, this could explain why treatments tested across different studies could not be directly compared to each other. Importance of accurate reporting of the test site locations.

Conclusions What does this study add? This study tested the anatomical differences of SLS-induced irritation in a trial with a larger sample size compared to previously conducted research. Baseline TWE, commonly used as an indicator of susceptibility to irritation, showed contrary results in this trial. This trial investigated anatomical differences in recovery To our knowledge, this is the first trial investigating anatomical difference in recovery under treatment.

The research team

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