Natural Insect Repellents Weaken in Hot Weather

A new study suggests that increasing temperatures could diminish the effectiveness of natural insect repellents. Researchers found that when exposed to heat, a mosquito pain receptor known as TRPA1 becomes less sensitive, reducing the insects’ ability to detect and avoid repellent chemicals.

TRPA1, sometimes referred to as the “wasabi receptor,” plays a role in detecting noxious heat and irritants in animals. In humans, activation of this receptor can cause eye and skin irritation. In mosquitoes, TRPA1 influences host attraction, particularly by helping them avoid substances that act as repellents.

Natural repellents less effective in extreme heat

Insect repellents function by creating a chemical barrier that discourages mosquitoes from approaching their target. However, the study found that natural compounds such as citronellal and catnip oil, which rely on TRPA1 activation, become less effective as temperatures rise.

To examine this effect, researchers removed mosquito TRPA1 receptors and expressed them in frog egg cells, a common laboratory technique for studying receptor proteins. They then exposed the receptors to citronellal and catnip oil at both normal and elevated temperatures. The results showed that while the receptors were activated, their sensitivity decreased significantly in hotter conditions.

Further testing involved live mosquitoes to observe their behavioral responses at different temperatures. When exposed to repellent compounds in conditions above 32 degrees Celsius, the mosquitoes were less likely to avoid the substances, indicating a potential reduction in repellent efficacy in natural environments.

Synthetic repellents remain effective

In contrast to natural repellents, a synthetic alternative, DEET, was not affected by temperature changes. Unlike citronellal and catnip oil, DEET does not rely on TRPA1 activation to repel mosquitoes, making it a more reliable choice in hot weather.

“This suggests that during the hottest days of the year you’d probably want to stick with a more conventional synthetic repellent and avoid using a natural product with citronella or catnip oil.”

Dr. Peter Piermarini. 

The researchers suggest that as climate change leads to more frequent extreme heat events, individuals may need to reconsider their choice of mosquito repellent. Synthetic repellents could offer more consistent protection in high-temperature environments, while natural alternatives may be less effective.

Future research aims to further explore the mechanisms behind TRPA1 desensitization at elevated temperatures and examine whether similar effects occur in real-world settings.

Reference: Park Y, Piermarini PM. Heat activation desensitizes Aedes aegypti transient receptor potential ankyrin 1 (AaTRPA1) to chemical agonists that repel mosquitoes. Pest Biochem Physiol. 2025;209:106326. doi: 10.1016/j.pestbp.2025.106326

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