Stratum corneum swelling and enhanced permeability can be induced by water exposure, so the scientist say that it was only logical to examine whether the application of modern high-performance sunscreens have any effect to skin barrier during water exposure.
This is the first study of its kind, evaluating water barrier functionality of such products in relevant clinical models, and was published in the International Journal of Cosmetic Science.
The researchers say that this added benefit of sunscreen shown in the study is both desirable and practical, as recreational sunscreens are made for outdoor activities which frequently involve extended water exposure periods.
“Extended beach and pool water exposure can compromise skin barrier. Topical application of hydrophobic sunscreen formulations can help resist the hygroscopic pressure caused by water exposure and help maintain the integrity of skin barrier,” say the team.
“The dual functions of sunscreen as UV and water barriers are unique and useful for the safety and health of skin in the summer.”
Sunscreen testing
In order to test whether sunscreen formulations can also serve as additional water barriers, the research team conducted trans-epidermal water loss (TEWL) measurement in a controlled water patch (including salt and chlorine water) model and then applied this relevant model to study the effects of pre-treatments of sunscreen sprays and stick.
They also conducted a water sorption–desorption test in vivo with and without sunscreens, before finally studying the effect of constant water exposure combined with a known irritant, sodium lauryl sulphate (SLS), in a randomized clinical trial.
The results showed that application of sunscreen formulations help mitigate water-induced barrier disruption by repelling water at skin surface. Pre-treatment of sunscreen also statistically decreased the irritation in an acute patch test model.
Water-resistant
People often wear water-resistant sunscreen formulations during extended period of water activities in the summer to protect skin from harmful UV rays.
Knowing that extended water exposure can cause stratum corneum swelling and a more porous skin barrier, and that hydrophobic, water-resistant sunscreen films that stay on the skin surface have the potential to resist , the team used this as the basis for their study.