With the heat arriving early, mosquitoes are already running rampant. More people are spraying repellents that mosquitoes dislike before heading to the mountains and fields. It's an easy way to repel mosquitoes, but if used incorrectly, it could instead attract them. When mosquitoes smell a repellent, they may approach more, judging it as a cue to feed on blood rather than to flee.
A joint team from the United States and France said on May 28 in the international journal Journal of Experimental Biology that "through a Pavlovian conditioning experiment, we confirmed that the mosquito repellent diethyltoluamide (DEET) can instead attract mosquitoes."
DEET is a representative mosquito repellent developed by the U.S. Army in 1946. It was initially thought to numb mosquitoes' sense of smell so they could not detect human body odor, but later it turned out that mosquitoes disliked the smell itself and fled. However, in this experiment, mosquitoes bit the arm of a researcher sprayed with DEET more often.
◇ Mosquitoes link repellent odor to blood
Russian physiologist Pavlov rang a bell every time he fed a dog. Later, the dog salivated at the sound of the bell alone. The researchers conducted an experiment to find out whether a repellent odor triggers conditioned reflexes in mosquitoes. They let mosquitoes feed on warm animal blood for 20 seconds and then sprayed DEET for 10 seconds. They repeated this process four times.
One researcher who served as the guinea pig placed both arms into a box containing mosquitoes that had undergone the Pavlov experiment. One arm was sprayed with DEET and the other was left as usual. Sixty percent of the mosquitoes flew to and bit the arm sprayed with DEET. Just as the dog in the Pavlov experiment anticipated food at the sound of the bell, the mosquitoes linked the smell of DEET with blood. Mosquitoes that did not undergo conditioned learning all avoided the arm that smelled of DEET.
The study was conducted by Claudio Lazzari, a professor at the Insect Biology Research Institute at the University of Tours in France, and his student, Clément Vinauger, a professor of biochemistry at Virginia Tech in the United States. Vinauger said, "This study shows that the mosquito brain can respond differently to chemicals based on experience."
Vinauger had previously confirmed through experiments that mosquitoes can learn and remember host-related odors. According to a paper released in 2023 in the international journal iScience, body washes with floral or fruity scents attract mosquitoes, while body washes with coconut scents have a repellent effect. Vinauger reasoned that DEET, depending on the situation, could also attract mosquitoes like body wash, and proceeded with the research.
◇ Repellent must be applied frequently to avoid backfiring
The researchers did not say people should avoid using DEET-based repellents. The Aedes aegypti used in this experiment transmits the dengue virus, which infects 400 million people worldwide every year, as well as the yellow fever virus, the chikungunya virus, and the Zika virus, which causes microcephaly in newborns, in which the brain does not develop properly.
Vinauger said DEET should be used actively in tropical regions where such mosquitoes are common. But it must be used properly. DEET's concentration decreases over time. If a mosquito feeds in this state, it may later use the repellent odor as a cue to find people. "DEET should be applied frequently rather than in a large amount at once to maintain repellent effectiveness," Vinauger said.
Mosquito repellents containing DEET are also widely used in Korea. About one in three mosquito repellents contains DEET. However, as studies continue to report that DEET may be harmful to the human body, regulators are limiting age of use, concentration, and frequency. Korea's Ministery of Food and Drug Safety recommends products with 10% DEET or less from 6 months of age, and products with more than 10% up to 30% from age 12.
To address the problems of existing DEET repellents, scientists have developed natural mosquito repellents with no concerns about side effects. A team at the Federal University of Amapá in Brazil announced in May in ACS Omega, an international journal published by the American Chemical Society (ACS), that they developed a mosquito-repellent cream containing patchouli oil. Earlier, U.S. scientists also identified components on human skin that repel mosquitoes. All act as a "cloak of invisibility," numbing mosquitoes' sense of smell and masking human body odor.
◇ Natural mosquito repellents found in flowers and on skin
Patchouli is a perennial herb in the mint family native to Southeast Asia. Oil extracted from patchouli has a deep, earthy scent and is widely used in perfumes and cosmetics. The Brazilian team hypothesized that patchouli fragrance overwhelms mosquitoes' sense of smell and prevents them from detecting people.
The problem is that oils extracted from plants evaporate easily. This is why the effects of natural insect repellents do not last long. The researchers combined oil extracted from patchouli leaves with an unscented cosmetic cream to create a mosquito-repellent lotion. Healthy men and women ages 20 to 35 were instructed not to use other cosmetics for 12 hours and to place their arms into a box with 50 Aedes aegypti mosquitoes.
In the experiment, arms treated with patchouli oil lotion and DEET lotion had no mosquito bite marks at all, but the untreated arms had many bite marks. Whereas existing natural repellents are volatile and their effects fade quickly, the mosquito-repellent effect of the patchouli oil lotion lasted up to 3 hours.
Ulrich Bernier of the Agricultural Research Service (ARS) at the U.S. Department of Agriculture announced at the American Chemical Society's annual meeting in 2013 that volatile compounds on human skin, such as 1-methylpiperazine, can interfere with mosquitoes' olfactory detection.
Human skin gives off a smell that mixes substances secreted by sweat and bacteria. Mosquitoes can detect that odor from as far as 30 meters away. People who are rarely bitten by mosquitoes effectively have such natural mosquito repellents on their skin. Since then, various efforts have continued to develop skin odor components into mosquito repellents, but none have been commercialized like DEET so far.
References
Journal of Experimental Biology (2026), DOI: https://doi.org/10.1242/jeb.251935
ACS Omega (2026), DOI: https://doi.org/10.1021/acsomega.6c00802
iScience (2023), DOI: https://doi.org/10.1016/j.isci.2023.106667
ACS (2013), https://www.acs.org/pressroom/newsreleases/2013/september/toward-making-people-invisible-to-mosquitoes.html