Sunscreen: do not mix it with mosquito repellent on your skin

This is the first time a scientific team has examined the combined effect of these two products, used by millions of people during the summer. The goal was to replicate as closely as possible the real-life conditions of human skin exposure to these substances, taking into account the rise of the tiger mosquito in many parts of the world.

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5 things to know about the tiger mosquito

In fact, the name "tiger mosquito" can easily mislead people about the shape and color of the Aedes albopictus (the scientific name for the tiger mosquito). It is actually small (smaller than a 1 euro cent coin) and is not striped yellow and black like the tiger mosquito, but rather black and white. Other distinctive features, and unlike many other mosquitoes, are that it does not strike at night but during the day. It is also silent.

For this study, the researchers used human skin biopsies, taken and preserved under optimal ex vivo conditions. These samples were then exposed to artificial and natural ultraviolet rays—emitted by the sun—after successively applying sunscreen and mosquito repellent, among the best-selling brands in France.

The analysis was then carried out using innovative software developed by a partner company in the study. This artificial intelligence, based on deep learning, made it possible to examine with great precision the reaction of the different layers of the skin to UV radiation. In particular, it measured cellular stress markers, key indicators of potential sun damage.

The results are clear: "Analysis of these data points to a reduction in UV protection in the case of a mixture of sunscreen and mosquito repellent," the CNRS said in a press release . In other words, the chemical interaction between certain components of these two products could reduce their effectiveness, particularly that of the sunscreen.

As for so-called "combination" products, which claim to have both a repellent and sun protection effect, the data are "less definitive." Further studies are needed to confirm and expand on these initial findings.

For effective protection, researchers recommend not applying these two products simultaneously, nor mixing them in your hand before use. It's best to apply the sunscreen first, waiting for it to absorb well into the skin—at least 15 to 20 minutes—before adding the repellent.