The bug spray on your bathroom shelf may not be working quite the way you think it does, and new research explains exactly why that might be happening.
A study published May 28, 2026, in the Journal of Experimental Biology by researchers from the University of Tours, France, and Virginia Tech found that Aedes aegypti mosquitoes — the species that transmits dengue fever, Zika virus, yellow fever, and chikungunya — can be conditioned to shift their behavioral response to DEET from aversion to attraction. In a form of Pavlovian learning, mosquitoes repeatedly exposed to DEET while feeding on warm blood came to associate the chemical's scent with a meal reward. In subsequent tests, those trained mosquitoes moved toward DEET-treated human skin rather than away from it.
As Science News reported, the researchers used a training protocol in which mosquitoes were restrained behind mesh while warm blood was placed just out of reach. As the insects began feeding, DEET was introduced. After repeated sessions, the mosquitoes had learned the association. In subsequent behavioral tests, the trained mosquitoes "actually bit people who were soaked in DEET more than those who wore no repellent at all," according to The Scientist's coverage of the study.
"Our study aimed at better understanding what makes DEET a repellent," said study co-author Clément Vinauger, associate professor of biochemistry at Virginia Tech, in an interview with Chemical & Engineering News. "Is it something intrinsic to its chemical structure, or is it about how mosquitoes interpret the molecule in a way that can be modified by their prior experiences? Turns out, it's more of the latter."
What This Means for Your Repellent Strategy — and When DEET Still Works
The finding raises an immediate practical concern: if a mosquito has previously fed in the presence of DEET — for example, biting through thin fabric treated with repellent, or feeding on exposed skin where DEET has worn off from an earlier application — it may be conditioned to approach rather than avoid DEET-treated people in the future.
Lead researcher Claudio Lazzari of the University of Tours stated the concern directly: "If mosquitoes are repeatedly exposed to DEET, it becomes less effective as a repellent," raising concerns that in some situations the repellent may even begin to attract some biting insects, according to the companion commentary published in the same issue.
But researchers and outside experts caution against abandoning DEET entirely — because the picture is more complicated than the headline suggests. Anandasankar Ray, a neuroscientist at the University of California, Riverside, who was not involved in the study, noted that mosquitoes also detect DEET through their legs when they land, not only through olfactory sensing in flight: "You'd be getting the smell of DEET being paired with a bitter touch contact." Because mosquitoes need to land on skin to feed, DEET's contact-deterrent effect — independent of its olfactory repellent effect — remains an important barrier. A mosquito that is attracted to the smell of DEET may still be deterred from landing and biting.
The study results from Phys.org's summary also confirm that this learning effect only occurs through repeated conditioning in a controlled setting — it is not a universal property of wild mosquito populations that have never previously fed in the presence of DEET. However, in high-density mosquito environments where DEET use is common and inconsistent, the training effect is plausible.
| Key Findings From the DEET Study | Detail |
| Study organism | Aedes aegypti (yellow fever mosquito) |
| Diseases transmitted | Dengue, Zika, yellow fever, chikungunya |
| Mechanism of conditioning | Pavlovian learning — DEET scent paired with blood meal |
| Result in trained mosquitoes | Active movement toward DEET-treated skin |
| Contact deterrence (legs) | Still operates independently of olfactory learning |
| Implication for reapplication | Inconsistent/worn-off DEET may promote conditioning |
| Published in | Journal of Experimental Biology (May 28, 2026) |
What to Do Now — Beyond DEET Alone
Experts are not calling for people to stop using DEET, but they are calling for smarter use and for diversification of repellent strategies, particularly in areas with active dengue, Zika, or other Aedes aegypti-borne disease transmission.
The EPA currently approves four active repellent ingredients as effective against mosquitoes: DEET (the most-tested, most data-backed), picaridin (also called icaridin), IR3535, and oil of lemon eucalyptus (OLE or PMD). Picaridin in particular has been recommended by the CDC and WHO as a comparable alternative to DEET with a lower-odor profile and similar duration of protection. Using picaridin-based repellents on days when DEET is not being applied, or alternating between them, reduces the risk that any individual mosquito population develops a conditioned preference for DEET's scent.
Reapplication timing matters significantly. DEET's repellent effect lasts two to eight hours, depending on concentration. A 10% DEET formulation lasts approximately two hours; 25–30% formulations protect for up to eight hours. Allowing protection to lapse, and then reapplying, creates exactly the scenario in which a mosquito might feed while DEET is present during the period of lapsed protection, beginning the conditioning process. Reapplying before the prior application wears off, rather than after bites begin, is more protective.
Structural barriers, including EPA-registered picaridin or DEET-treated permethrin clothing, door and window screens, and elimination of standing water, remain the most reliable protections against Aedes-borne diseases. For residents and World Cup visitors in Houston, Miami, Dallas, and other dengue-risk cities this summer, layering these approaches, rather than relying on DEET alone, is the current public health best practice.
Frequently Asked Questions
Can mosquitoes actually be attracted to DEET?
According to the May 28, 2026 study in the Journal of Experimental Biology, Aedes aegypti mosquitoes can be conditioned through repeated exposure to associate DEET's scent with a blood meal. In controlled experiments, trained mosquitoes moved toward DEET-treated skin and bit DEET-treated individuals more than untreated controls. However, this is a conditioned learned behavior — not an innate preference — and requires repeated exposure paired with feeding to develop.
Should I stop using DEET?
No. Leading researchers and outside scientists emphasize that DEET remains effective and that its contact-deterrent effect through skin-landing mechanisms operates independently of the olfactory learning described in the study. The takeaway is that reapplication timing matters and that diversifying repellent strategies with alternatives like picaridin is advisable for consistent protection.
What mosquito repellents should I use besides DEET?
The EPA approves picaridin (icaridin), IR3535, and oil of lemon eucalyptus (OLE/PMD) as effective mosquito repellents alongside DEET. Picaridin in particular is recommended by the CDC and WHO as a comparable alternative. Wearing permethrin-treated clothing adds a structural barrier that operates independently of spray repellents.
Which diseases are carried by the Aedes aegypti mosquito?
Aedes aegypti is the primary vector for dengue fever, Zika virus, yellow fever, and chikungunya — all diseases that infect tens of millions of people worldwide annually. This species is present in parts of Texas, Florida, California, and other southern states, and is the subject of all World Cup dengue health warnings in U.S. host cities.
When should I reapply DEET for best protection?
DEET lasts approximately two to eight hours depending on concentration (10% = ~2 hours; 30% = up to 8 hours). Reapply before the prior application wears off, not after bites begin. Allowing protection to lapse and then reapplying is the scenario most likely to contribute to Pavlovian conditioning in local mosquito populations.
