Studies rule out the effectiveness of electronic repellents, bracelets, and citronella candles against insects.
14ymedio/SINC/Javier Yanes, Madrid, July 25, 2026 – Mosquitoes transmit about 78 diseases that, according to some estimates, cause up to one million deaths each year, 600,000 of them from malaria. In Cuba, where mosquito control campaigns were a public health priority for decades, the economic crisis and the deterioration of public services have weakened that response capacity.
The dengue and chikungunya epidemic that swept across the Island beginning in 2025 found favorable conditions due to the lack of fumigation, the accumulation of garbage, and difficulties in diagnosing and treating patients. In February of this year, the Pan American Health Organization reported two new chikungunya deaths in January, bringing the total number of deaths recorded by the organization to 67, along with 1,457 cases of the disease during that month.
How can we protect ourselves from mosquitoes? While science searches for new weapons against this pest, the best option remains to rely on methods whose effectiveness has been proven. Despite their popularity, this does not include certain remedies that have been shown to be useless.
DEET “remains the most widely used, the most effective, and the least expensive in the world”
During World War II, troops deployed in tropical regions suffered from mosquito-borne diseases. Sixty percent of U.S. soldiers in the Pacific contracted malaria, while another 5% came down with dengue. In total, 1.2 million suffered from one or both infections. Although mortality was low, the impact on military operations was so severe that it forced the U.S. government to seek solutions.
At the time, insect repellents such as citronella oil (lemongrass) were already in use, but they were not effective enough. Beginning in 1942, scientists such as chemist Samuel Gertler of the Department of Agriculture tested more than 7,000 compounds in search of new formulas to protect against insects. That was how Gertler discovered DEET (diethyltoluamide). Patented in 1946, after the war, it was kept as a closely guarded military secret until civilian use was authorized in 1957.
DEET has stood the test of time: eighty years later, it remains the benchmark repellent. “It is still the most widely used in the world, the most effective, and the least expensive,” Claudio Lazzari, a biologist specializing in disease-carrying insects at the University of Tours (France) and the University of Buenos Aires, told SINC.
Higher concentrations are recommended for regions at risk of malaria and other mosquito-borne diseases
DEET is the reference standard against which any new candidate is measured. It is sold under numerous brand names and in different concentrations; higher concentrations provide longer-lasting protection, up to eight or nine hours, although protection does not appear to increase significantly beyond 50%. Higher concentrations are recommended for regions at risk of malaria and other mosquito-borne diseases.
DEET’s long history also supports its safety, and it can even be used on babies as young as two months old. According to Lazzari, at very high concentrations, around 75%, “it has been associated with allergic reactions and some toxicity,” but “no commercial repellent contains that much in its formulation.”
In addition, although it is moderately harmful to aquatic organisms, it biodegrades slowly and therefore does not tend to accumulate.
In short, DEET is the closest thing we currently have to the perfect repellent. But it has one major drawback: it is unpleasant to use. Its oily texture leaves the skin greasy, and, even worse, it dissolves plastic, meaning it can damage many objects or materials that come into contact with the skin, including bracelets, sandals, watchbands, sunglasses, nail polish, or synthetic fabrics such as elastane or Lycra.
“Alternatives, especially natural ones, tend to be more expensive, provide less protection, and are not usually completely harmless”
This shortcoming of DEET leaves room for other options, although, Lazzari warns, “alternatives, especially natural ones, tend to be more expensive, provide less protection, and are not usually completely harmless.” These other repellents include traditional citronella oil, Merck’s IR3535, or distilled oil of lemon eucalyptus (OLE), enriched with an active ingredient called para-menthane-3,8-diol (PMD). However, this is not the essential oil extracted directly from the plant, which is sometimes falsely marketed as a repellent.
However, study after study reaches the same conclusion: the protection provided by citronella oil and other plant oils fades quickly because of their high volatility, dropping by half after two hours, whereas DEET’s protection remains. Although PMD is an option, DEET’s strongest competitor is picaridin, also known as icaridin, developed by Bayer in the 1980s. It is the only repellent that has matched DEET’s performance in tests, without damaging plastics or leaving a greasy feel. Concentrations of 20% provide the same level of protection as DEET.
It is possible that new repellents will be discovered in the future, but this search faces a major obstacle: despite DEET’s long history, scientists have still not resolved exactly how it works. “There is no general model explaining why repellents repel,” Lazzari points out. There are at least three hypotheses, each supported by experimental evidence: “That they block mosquitoes’ ability to detect us, that they are toxic and affect the nervous system, and that mosquitoes smell them and avoid them.”
“The more we understand how mosquitoes process odors, the better we will be able to design more precise repellents”
This last idea is supported by a recent study led by Lazzari that revealed a surprising result: mosquitoes exposed to a puff of DEET while feeding can learn to associate its smell with food, causing the repellent to become an attractant for them.
It is the classic conditioning demonstrated by Pavlov’s dogs, which salivated in response to a stimulus associated with food. This indicates that, for mosquitoes, DEET’s action is not purely mechanical but also has a cognitive component.
Humanity’s battle against pests has repeatedly encountered this kind of obstacle: over time, one way or another, our enemies eventually find ways to resist, avoid, or tolerate the weapons we use against them.
Although DEET remains widely effective for now, “the fact that we do not know exactly why mosquito behavior changes in this way is a major obstacle to the search for new molecules,” says Lazzari.
In recent years, research has delved deeper into the mosquito’s systems that guide it toward humans, beginning with the odor of substances we emit, such as carbon dioxide from our breath, lactic acid, and other metabolic products and skin bacteria. “The more we understand how mosquitoes process odors, the better we will be able to design more precise repellents,” Floris van Breugel, a researcher at the University of Nevada, Reno, whose studies have shed light on this field, told SINC.
“The fact that we do not know exactly why mosquito behavior changes in this way is a major obstacle to the search for new molecules”
Researchers are therefore looking for compounds that interfere with mosquitoes’ sense of smell or confuse them, enhancing the effect of repellents. Although more extensive testing is still needed, substances have already been identified that provide longer-lasting protection than DEET.
According to Lazzari, this knowledge makes it possible to design “rational strategies,” such as the one he is developing through a collaborative project between Argentina and France. “The idea is to test molecules that are likely to trigger an avoidance response, such as bitter substances.”
Repellents are a primary resource in areas at risk of mosquito-borne diseases, but they are not the only means of personal protection. The most traditional basic measure is a physical barrier such as a mosquito net, especially one treated with widely available insecticides such as permethrin. The World Health Organization has recently added a new recommendation for malaria control: the use of so-called emanators, or spatial repellents, systems that gradually release insecticides into the air.
On the other hand, environmental concerns argue against ultraviolet mosquito lamps. Studies have shown that they attract very few mosquitoes but many beneficial insects, such as moths. In one sample, only 31 out of 13,789 insects killed in the trap were mosquitoes.
“Many of the products marketed as repellents that have been tested do not reduce mosquitoes’ attraction to humans.”
As for other types of measures, at best they may provide slight help; at worst, they are completely useless. One example is one of the most popular supposed mosquito defenses available in stores every summer: citronella candles. Although citronella oil works as a repellent when applied to the skin, there is absolutely no guarantee that burning wax mixed with this substance will repel insects.
In fact, it does not. A study by New Mexico State University comparing various mosquito control methods concluded that “the citronella candle has no effect whatsoever.” The authors added that “many of the products marketed as repellents that were tested do not reduce mosquitoes’ attraction to humans.”
Among these major failures are two other popular products: repellent bracelets and electronic ultrasonic mosquito repellents.
“Our hypothesis is that the concentrations released by the tested bracelets are too low to have any effect”
As for the bracelets, one study found a 30% reduction in bites when using a DEET-treated bracelet, but only on the arm wearing it. Regarding bracelets containing citronella or other plant extracts, the New Mexico study found no benefit.
“Our hypothesis is that the concentrations released by the tested bracelets are too low to have any effect,” the authors wrote, emphasizing that a compound that works in one form does not necessarily work when used differently—for example, a topical repellent incorporated into bracelets.
Even worse are electronic devices that claim to repel mosquitoes with ultrasound. Time and again, tests have shown that they do not deter mosquitoes at all.
“Field entomological studies confirm that electronic mosquito repellents have no effect whatsoever in preventing bites,” wrote the authors of a review of the available studies.
“Field entomological studies confirm that electronic mosquito repellents have no effect whatsoever in preventing bites”
The same applies to smartphone apps. According to the New Mexico study, any system claiming to repel mosquitoes with sound is “the modern equivalent of snake oil,” a reference to fraudulent remedies.
The list of false anti-mosquito claims is endless. For example, some people claim that certain foods or supplements, such as vitamin B1 (thiamine), yeast, or garlic, protect us from mosquito bites.
According to National Taiwan University entomologist Matan Shelomi, who reviewed the available studies, “the scientific consensus is unequivocal that oral repellents do not exist. Despite extensive searches, no food, supplement, medication, or condition has ever been proven to make people repellent to mosquitoes.” The New Mexico study also tested vitamin B1 patches applied to the skin. The verdict: they do not work either.
The same drawer of failed remedies also includes so-called repellent plants, as emphasized by medical entomologist Cameron Webb of the University of Sydney.
This expert also warns about mosquito-repellent clothing. Although garments treated with permethrin or other insecticides provide better protection than untreated clothing, “they are unlikely to prevent mosquito bites on exposed areas of the skin.” Furthermore, “after washing, any protection these garments provide is likely to decrease.” At the very least, covering the entire body remains a measure that never fails.
Translated by Regina Anavy
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