A new study conducted by CNRS researchers on the combined use of sunscreen and an insect repellent that is among the best selling in France during summer concludes that UV2 protection decreases after application of the mixture. With the spread of tiger mosquitoes in many countries, 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 studies the effects of such a mixture. It has been published in Parasites & Vectors.

In order to reproduce the real conditions to which the human epidermis is subjected as faithfully as possible, scientists have used skin biopsies. Optimally preserved ex vivo, these 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, they 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 of these data 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.

Many other product mixtures, including cosmetics, have never been studied as such. This new analytical method, combining the use of biopsies (more reliable than tests on in vitro cultured cells) and artificial intelligence, would now allow the examination of their effects on human health.