Mosquitoes Are Now Using Your Repellent to Find You
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Time to read 3 min
Every summer, the same ritual. Spray on the mosquito repellent, hope for the best, scratch the bites you somehow got anyway. DEET, the active ingredient in most mosquito repellent products sold worldwide, has been the gold standard in insect protection since the 1940s, recommended by the World Health Organisation and credited with saving countless lives in malaria and dengue-endemic regions. A new study published this week suggests the picture may be more complicated than we thought.
The good news: mosquito repellent still works.
The less comfortable news: mosquitoes can learn.
What the Study Found
Claudio Lazzari, professor at the Insect Biology Research Institute at France's University of Tours, ran what amounts to a Pavlov's dog experiment, but with mosquitoes instead of dogs, and blood instead of a bell.
In the original Pavlov experiments, dogs were repeatedly presented with food at the same time as a neutral stimulus: a sound. Eventually the sound alone triggered salivation, because the dogs had learned to associate it with eating. Lazzari and colleagues replicated this structure with Aedes aegypti, the yellow fever mosquito that also transmits dengue, Zika, and chikungunya.
Hungry mosquitoes were placed in a mesh enclosure and presented with warm sheep's blood, while being simultaneously exposed to a gentle breeze of DEET-scented air. The researchers then presented their own hands: one treated with mosquito repellent, one untreated.
The result was striking. Sixty percent of the conditioned mosquitoes flew toward the mosquito repellent-treated hand and attempted to bite it. Mosquitoes that had not been conditioned did the opposite: they avoided the repellent entirely, as expected.
The full study is published in the Journal of Experimental Biology.
Does This Mean Mosquito Repellent Doesn't Work?
No, and the researchers are emphatic on this point.
The results were conducted "under very specific conditions" in the lab and do not "call into question the effectiveness" of mosquito repellent, lead author Lazzari told AFP. Lazzari added that DEET is still the most effective mosquito repellent available, protecting people from mosquito-borne diseases. "It saves lives!", he said.
The key limitation is physical: mosquitoes also smell with their legs. When they land on mosquito repellent-treated skin, the bitter contact repels them before they can feed, meaning mosquito repellent still does its job at point of contact, even in trained insects. The training effect matters at the stage of approach, not landing.
Bug spray alone was never enough. Long sleeves, bed nets, and avoiding dawn and dusk are just as important.
So What Is the Real Risk?
The real-world concern centres on what happens when mosquito repellent wears off.
"If someone applies mosquito repellent and the concentration fades over time, but a mosquito still manages to feed, the insect may begin associating that smell with a reward," said Clément Vinauger, co-author and biochemist at Virginia Tech. "That's a possibility we should take seriously when we think about how mosquito repellent is used in the real world."
The scenario: you apply mosquito repellent in the morning. By afternoon, the concentration has dropped: you're sweating, you haven't reapplied. A mosquito manages to feed. From that point, it has learned to associate the smell of mosquito repellent with food. The next time it encounters someone wearing the same product, it may be more likely to approach rather than retreat.
Vinauger's practical advice: "Instead of applying a lot at once, you may want to reapply regularly so it's always active and providing continuous protection."
What You Should Actually Do
Reapply regularly. The learning effect kicks in when mosquito repellent concentration drops below the threshold of full repellency. Follow the label and reapply every two to four hours, especially if you are sweating.
Don't rely on mosquito repellent alone. Long sleeves and trousers dramatically reduce exposed skin. Bed nets, particularly insecticide-treated nets, are the single most effective barrier against night-time biting. Avoid the outdoors at dawn and dusk, when mosquito activity peaks.
Choose the right concentration. Mosquito repellent products vary significantly in DEET concentration. Higher concentrations provide longer-lasting protection, not stronger protection. For extended periods in high-risk environments (a safari, a jungle trek, a river cruise) higher concentrations or alternatives such as picaridin are worth considering.
Consider picaridin as an alternative mosquito repellent. Picaridin (also known as icaridin) is now recommended alongside DEET by the WHO. It is odourless, less greasy, and there is currently no evidence of a similar learning vulnerability. It does not replace DEET as the gold standard mosquito repellent, but it is a credible alternative for everyday use.
A Note on Mosquito-Borne Disease
The study focuses on Aedes aegypti, the vector for dengue, Zika, chikungunya, and yellow fever. These diseases are expanding geographically due to climate change, urbanisation, and international travel. Malaria, transmitted by Anopheles mosquitoes, is a separate species not studied in this research, though the broader question of mosquito repellent resistance is relevant across vectors.
If you are travelling to a destination where mosquito-borne disease is a genuine risk (tropical Africa, Southeast Asia, parts of South America) mosquito repellent is not optional. Apply it correctly, reapply regularly, and combine it with physical barriers. That combination remains the most effective protection available.