Do mosquito repellents reduce the effectiveness of sunscreens?

However, while mosquito repellents and sunscreens are summer essentials, a recent study questions their compatibility. To assess their interactions, human skin biopsies were used ex vivo, enabling reproduction of real-life conditions. Three products were tested: a repellent containing 35% IR3535; an SPF 50 sunscreen formulated with avobenzone, octyl triazone, and anisotriazine as UV filters; and a hybrid product combining these filters with plant extracts, including lemon eucalyptus essential oil.

The products were applied alone (50 μL) or in combination (25 μL each), starting with the sunscreen. The reverse order of application (repellent first, then sunscreen) was not tested—this comparison might have yielded different results. After 30 minutes of incubation, explants were exposed either to intense UVB radiation (300 mJ/cm²) for 3 minutes or to natural sunlight with a UV index of 8 for 2 hours (144 mJ/cm²). Two controls were included: a skin explant exposed to sun without protection (positive control) and one unexposed (negative control). Skin structure was examined using hematoxylin and eosin staining. Researchers evaluated several parameters, including cell nucleus morphology, density, and their distribution in the epidermis.

Using computational analysis, researchers extracted a high contrast mean value (HCM), a quantitative indicator of halo formation around cell nuclei in histological images. These halos correspond to areas of cytoplasmic disorganization and suggest a cellular apoptosis that may be induced by UV. The HCM measured 24 to 48 hours after UVB exposure are shown in histograms A and B below.

Two applications of a sunscreen containing avobenzone, octyl triazone, and anisotriazine and a mosquito repellent containing IR3535 reduce sun protection.

When sunscreen is applied alone, HCM remains comparable to that of unexposed explants, confirming its expected efficacy. In contrast, applying repellent after sunscreen results in a significant decrease in protection, with values similar to those observed without photoprotection. These results suggest that the repellent alters the efficacy of UV filters, or neutralizes them completely. It is notable that the hybrid product, designed to offer dual protection against mosquitoes and UV radiation, provides only minimal sun protection in this test, which calls its efficacy into question.

We can also question another point: HCM values at 48 hours sometimes fall below those at 24 hours, which is counterintuitive. This decline could indicate progressive product degradation, partial elimination of active compounds, or partial cell recovery in the absence of renewed exposure. We can assume citronella essential oil in this product has altered the distribution or stability of UV filters, reducing their protective capacity. It is also possible that combining these ingredients modifies the product’s refractive index, reducing UV ray absorption.

A study published in 1997 made a similar observation: the simultaneous application of a DEET-containing repellent and a sunscreen formulated with ethylhexyl methoxycinnamate, oxybenzone, and ethylhexyl salicylate had reduced the sun protection factor by 28% in 14 volunteers. These results, echoing recent observations, suggest that the interaction between certain repellents and UV filters could compromise sunscreen efficacy.

No explanation has been provided for how mosquito repellents and sunscreen products might interact. Possible mechanisms include UV filters degrading through reactions with repellent compounds, mechanical alteration, or dilution. Experiments tested a limited number of products: one repellent and one sunscreen in laboratory conditions, plus another combination tested in 1997. There are 27 UV filters regulated in Europe, including both chemical and mineral filters, and not all interact with mosquito repellents.

Scientists tested sunscreen efficacy alone, with mosquito repellent, and with the hybrid product during a two-hour sun exposure (histogram C). The results are less conclusive. Unlike UVB-only exposure, sunscreen alone no longer provides adequate protection. The HCM value in this condition matches that obtained with the sunscreen-repellent combination or with the hybrid product, which suggests reduced efficacy. This finding is notable. It indicates that even without repellent, sunscreen protection declines during prolonged exposure to natural sunlight. We can hypothesize that UV filters degraded during exposure. In any case, these data do not allow a conclusion on the interaction between sunscreen and mosquito repellent under normal exposure conditions.

Despite the relevance of the initial results, additional real-world studies with a larger sample and varied formulations would clarify interactions between repellents and sunscreen products.

How can you combine sunscreen and mosquito repellent?

A possible incompatibility between sunscreen and insect repellent does not require giving up either product. While we await more data on this interaction, we recommend youwait at least 20 minutes the application of these products. In line with CDC recommendations, apply sunscreen first so filters adhere to the skin, then follow with insect repellent. Also reapply the sunscreen, after swimming, sweating, or every two hours, to maintain protection throughout exposure.