DEET: Mosquito Repellant or Attractant?

“[A] new study suggests that, as Pavlov’s dogs learned to associate the ringing of a bell with food, so mosquitoes can learn that the presence of DEET indicates the possibility of a blood meal.”

Nicola Davis, science correspondent, The Guardian

“If mosquitoes are repeatedly exposed to DEET, it becomes less effective as a repellent.”Claudio Lazzari, University of Tours, France

No one likes being bitten by mosquitoes. But, mosquitoes are not just annoying, pesky insects; they are the world’s deadliest animal carrying diseases that kill hundreds of thousands of people annually.    

In the 1940s, chemists at the U.S. Department of Agriculture developed DEET, the gold standard insect repellent. DEET seemed to solve the biting problem thereby protecting people from mosquito-borne diseases.

Now, barely one month into mosquito season in North America, there is a new study that shows that mosquitoes can develop a taste for DEET. This has raised concerns that, in some situations, DEET may begin to attract these insects. That study is the focus of this week’s post.

Mosquito, deadliest animal on Earth. Scientist have identified over 3,500 mosquito species but only a small fraction of these —less that 10%—bite humans. The three main genera that do are:

1. Aedes—950 species including the highly aggressive day-biters that transmit dengue, Zika, and yellow fever;

2. Culex—the vector for West Nile virus; and

3. Anopheles— about 430 species, including the only species that transmit human malaria.

These three mosquito genera transmit diseases that cause more than 700,000 deaths per year globally, making the mosquito, overall, the deadliest animal to humans. (The approximate number of human deaths caused by homicide, war, and violence is estimated at between 400,000 to 500,000 per year—about 100,000 deaths shy of malaria-related deaths.)

Antarctica is the only continent with no mosquitoes and, until recently, Iceland was the only mosquito-free country in the world. Last fall, the Icelandic Institute of Nature History confirmed the first “natural occurrence of Culiseta annulata mosquitoes in the land of fire and ice—two females and one male.” (Bassi, M., “Iceland was the only country in the world without mosquitos—now they’ve found three,” Popular Science, October 23, 2025).

Mosquito repellents. Mosquito repellents are a time-honored way to prevent mosquitoes from biting and thereby protecting oneself from acquiring a mosquito-borne disease. DEET has been  unsurpassed in repelling mosquitoes; it is the most widely used insect repellent in the world.

A common assumption is that DEET works because of its chemistry; it either blocks mosquitoes from smelling us or smells terrible to mosquitoes. DEET appears to work by affecting mosquitoes’ smell (olfaction), taste (gustation) and behavior.  It interferes with how mosquitoes detect human odor cues such as carbon dioxide, lactic acid, and skin-derived volatile compounds. When a mosquito lands on skin sprayed with DEET, receptors on the mosquito’s legs and mouthparts detect the chemical. (Dennis, E.J., et al., “Aedes aegypti mosquitos use their legs to sense DEET on contact,” Current Biology, April 25, 2019). It tastes unpleasant to most mosquitoes and prevents them from feeding. It can also alter flight patterns, host-seeking behavior, and landing decisions.

Repellent becomes attractant (or when DEET is a call for dinner). Researchers at the University of Tours in France and Virginia Tech recently published a study that suggests a mosquito’s reaction to DEET may be modified by experience, that is, a mosquito can learn to associate the smell of DEET with a blood meal. (Lazzari, C.R., et al., “Associative learning switches DEET valence from aversive to appetitive in Aedes aegypti,” Journal of Experimental Biology, May 28, 2026). This study represents a significant challenge to long-held assumptions of how DEET works and what mosquitoes may be capable of learning. (Bergson, L, “The scent of supper: Can mosquitoes learn to Love DEET?,” CIDRAP News, May 29, 2026).

Using a form of Pavlovian conditioning, the researchers trained mosquitoes to associate DEET with food. They placed a bag of warm sheep’s blood just out of reach in the mosquitoes’ enclosures for 20 seconds and then squirted in the scent of DEET for the final 10 seconds of dining. They completed this process four times before checking on how the insects responded to the scent of DEET alone. More than 60% of the trained mosquitoes tried to take a bite from the out-of-reach bag when they caught a whiff of DEET. (Knight, K., “Inside JEB: DEET insect repellent at risk: mosquitoes can learn it means dinner,” Journal of Experimental Biology, May 28, 2026).

The researchers then offered the trained insects the choice of a team member’s hands, one was clean the other bathed in DEET. The insects tried to bite the DEET-scented hand. Finally, the researchers tried another strategy. They attempted to train the mosquitoes to associate the scent of DEET with a sugary treat. The mosquitoes bit “enthusiastically whenever they picked up the scent of DEET.”

This study shows it is possible to condition mosquitoes to associate the scent of DEET with the prospect of a meal. Under the right circumstances, this could make people wearing DEET more attractive to biting insects.

Don’t ditch the DEET. An important caveat to consider when reviewing these findings is these were lab-bred mosquitoes and the experiments were conducted in a very particular controlled setting. No one knows whether this phenomenon—mosquitoes being attracted to DEET— happens in the real world. (M Bassi, “Could Bug Spray Attract Mosquitoes? Lab Insects Learned That the Smell of DEET Would Lead Them to a Tasty Treat,” Smithsonian Magazine, June 1, 2026).

The data does, however, offer guidance on the most effective way to use insect repellants. It highlights the importance of following the manufacturer’s recommendations for dosage and reapplication frequency in order to reduce the risk of mosquitoes learning to outsmart the repellants. According to co-author Professor Claudio Lazzari from University of Tours,  “If a mosquito bites someone who has applied DEET to their skin several hours earlier and the concentration of the repellent is too low to repel the mosquito, but still strong enough for the insect to smell it, the mosquito may be more likely to bite people who smell of DEET.”

The desired aversive effect of DEET may be dose-dependent. Nonetheless, DEET is still the gold standard for insect repellents. It protects people from mosquito-borne diseases. It saves lives. So, unless the laboratory-based switch to an attractant property is recognized in the real world: “Don’t Ditch the DEET.”