DEET has been the leading defense against mosquito bites for decades, but a new study suggests the world’s most widely used insect repellent may not always trigger the same response in mosquitoes.
Researchers found that mosquitoes can learn to associate DEET with a blood meal under certain conditions and later show attraction to the chemical.
The findings, published in the Journal of Experimental Biology, add a new layer to scientists’ understanding of how DEET works and how mosquito behavior may adapt through experience. The study was led by Claudio Lazzari of the University of Tours in France.
Questions remain about how DEET works
DEET, formally known as N, N-diethyl-meta-toluamide, has been used for more than 80 years. It remains a key tool for preventing bites from mosquitoes that can spread diseases such as malaria, dengue, chikungunya, Zika, and yellow fever.
Despite its long history, scientists still debate exactly how the repellent works. Earlier studies suggested DEET interferes with mosquitoes’ ability to detect human odors, effectively confusing them rather than simply driving them away. Other research found that some mosquitoes show reduced sensitivity to the chemical and that this trait can be inherited.
Scientists have also observed signs that mosquito responses to DEET may involve learning. In one previous study, mosquitoes exposed to the repellent became temporarily less sensitive to it when they encountered it again within a few hours.
Researchers tested mosquito learning
To investigate further, the researchers designed a series of laboratory experiments. Mosquitoes were placed in small cages and presented with a warm blood-filled target that mimicked a host. The team measured movements of the insects’ proboscis, the mouthpart used for feeding, as an indicator of biting attempts.
The mosquitoes then underwent different training programs involving heat, DEET, and short opportunities to feed on blood.
Mosquitoes may be able to learn to associate #DEET with a blood meal and later show attraction to the world's most widely used insect repellent, according to a new study.
Researchers say the findings do not mean DEET has stopped working. pic.twitter.com/A6hAYNvvu0
— Tom Marvolo Riddle (@tom_riddle2025) June 2, 2026
The most striking results came from mosquitoes exposed to DEET while they were actively feeding. Afterward, those insects showed a significantly stronger biting response when they encountered DEET again. The findings suggest they had learned to associate the chemical with a rewarding blood meal.
The team also tested the behavior using a volunteer’s hands. One hand was treated with DEET while the other was left untreated. About half of the mosquitoes that had received the DEET-and-blood training attempted to bite the DEET-treated hand. Untrained mosquitoes consistently avoided the treated hand and chose the untreated one.
Findings highlight a possible limitation
The findings do not mean DEET has stopped working or that people should stop using it. The experiments were conducted under tightly controlled laboratory conditions, and the training process may not reflect how mosquitoes encounter repellents in everyday situations.
Still, the study suggests DEET may influence mosquito behavior through both sensory and cognitive processes. Researchers said a better understanding of those mechanisms could help improve future repellents as mosquito-borne diseases continue to spread worldwide.
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