The Effect of Sunscreens on the Skin Barrier.

Transepidermal water-loss (TEWL), stratum-corneum hydration (SCH), erythema, elasticity, pH and melanin, are parameters of the epidermal barrier function and skin homeostasis that objectively indicate the integrity of the skin barrier. Sunscreens are necessary to protect people from skin cancer, but could modify the skin barrier function. Nevertheless, there are not many studies on their impact on skin homeostasis. The aim of this study is to evaluate the impact of sunscreens on the epidermal-barrier function and skin homeostasis of healthy individuals. A prospective observational study was designed. TEWL, SCH, erythema, elasticity, pH and melanin were measured on the cheek and volar region of the forearm, using non-invasive methods before and after applying sunscreen. Four different sunscreens were tested, one full-body sunscreen and three facial sunscreens. The study included 51 healthy volunteers, 72.5% (37/51) women, with a mean age of 41.63 years. After full-body sunscreen application, temperature increased by 0.68 °C (p < 0.001), pH by 0.16 units (p < 0.001), and elasticity by 0.22% (p = 0.039), while melanin decreased by 10.95 AU (p < 0.001), erythema by 28.79 AU (p < 0.001) and TEWL by 0.66 g·m−2·h−1 (p = 0.019). On the cheek, facial sunscreen 1 increased temperature by 0.51 °C, TEWL 0.7 g·m−2·h−1 (p < 0.05), pH by 0.12 units (p < 0.001) and elasticity by 0.059% (p < 0.001), but decreased erythema by 19.87 AU (p < 0.05) and SCH by 5.63 AU (p < 0.001). Facial sunscreen 2 increased temperature by 0.67 °C, TEWL by 1.93 g·m−2·h−1 (p < 0.001), pH by 0.42 units (p < 0.001) and elasticity by 0.12% (p < 0.01), but decreased melanin by 15.2 AU (p = 0.000), erythema by 38.61 AU (p < 0.05) and SCH by 10.80 AU (p < 0.01). Facial sunscreen 3 increased temperature by 1.15 °C, TEWL by 2.29 g·m−2·h−1 (p < 0.001), pH by 0.46 units (p < 0.001) and elasticity by 0.15% (p < 0.01), but decreased erythema by 35.7 (p < 0.05) and SCH by 10.80 AU (p < 0.01). In conclusion, sunscreen could slightly modify the skin-barrier function. All of them decreased erythema, likely in relation to anti-inflammatory power.