Sunscreen formulations do not interfere with sweat cooling during exercise

Sweating plays a critical role in maintaining thermal balance and keeping skin cool during exercise. People often wear sunscreens on hot summer days for sun protection. Most recreational sunscreens are designed to be water- and sweat-resistant, so that sweating will not remove or compromise the protection. The objective of this study was to determine whether wearing sweat-resistant sunscreen might impede natural sweating, potentially interfering with thermal regulation and resulting in the elevation of skin temperature.

We conducted a controlled, randomized, split-face and split-arm clinical study with 24 female subjects wearing an SPF 70 lotion sunscreen on half of the face and an SPF 70 spray sunscreen on one of the forearms at a dosage of 2 mg cm^-2 . Following sunscreen application, subjects participated in two sessions of indoor exercise to induce clearly visible sweating.

We found that both skin temperatures and sweat evaporation rates were significantly elevated after each session, yet there were no significant differences in either skin temperatures or sweat rates between the treated and untreated control sites at any time point for any of the skin sites measured.

We conclude that the application of tested sweat-resistant sunscreen lotions and sprays does not have any measurable effects on skin cooling by natural sweating process. People should continue to use these sunscreens during recreational activities.