The combined use of insect repellant and sunscreen may reduce ultraviolet protection, a new study suggests.

It has become increasingly common for people to combine these two products during outdoor activities to protect themselves from both the sun and these pests.

This is the first paper that studied the effects of such a mixture. It is published in Parasites and Vectors.

Stress Responses Measured by AI

To reproduce the real conditions, optimally preserved ex vivo samples were subjected to artificial and natural UV rays emitted by the sun after application of sunscreen and repellent. Thanks to a new computer tool developed by one of the partner companies of this study, the samples were analyzed in the form of thin slices corresponding to the different layers of the skin. This software, a deep-learning artificial intelligence system, made it possible to measure the stress response of skin cells to the radiation.

The analysis points to a decrease in UV protection in the case of a mixture of sunscreen and insect repellent. For “mixed” products, presenting themselves as carrying both protections at the same time, the data obtained are less categorical. Further studies are needed to consolidate and extend these initial results.

PHOTO CAPTION: Histometric analysis of UVB-irradiated human skin biopsies after application of sunscreen and/or insect repellent or “combo” product. Skin samples (from the same donor) were treated with a sunscreen containing UV filters (panels d and e), or (panels c and e) a mosquito repellent containing the synthetic active ingredient IR3535, or a commercial preparation composed of a natural insect repellent and a sunscreen (f) (“combo spray”). Except in the control condition (panel a), skin biopsies were previously exposed to UVB irradiation under controlled conditions (300 mJ/cm2). Histological sections stained with saffron hematoxylin-eosin. Scale bar: 50 µM. Inset details show areas of interest with haloed nuclei (reflecting cellular damage) indicated by arrows