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Certain Brands of Soap May Have Mosquito-Repelling Scents

A pile of soaps.
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Mosquitoes’ ability to transmit deadly diseases like dengue fever and Zika makes them a blight on all of humanity. But they show a clear preference for some unlucky individuals over others. A new discovery suggests that a simple hygiene shift could change how tasty mosquitoes find you.

Odor combinations make the difference

A scientific study published in the journal iScience has suggested that certain types of soap can be a mosquito magnet or deterrent. The exact effect of the soap appears to vary, as its scent interacts with each person’s unique odor.

Senior author and neuroethologist at Virginia Tech Clément Vinauger explained the magnitude of the effects: “The same individual that is extremely attractive to mosquitoes when they are unwashed can be turned even more attractive to mosquitoes with one soap, and then become repellent or repulsive to mosquitoes with another soap.”

A history of soapy smells

Humans have used soap and other strong-smelling hygiene items since time immemorial. We know they change how we smell to other humans, but how they might change insects’ perception of our aroma has not been investigated.

To answer this question, researchers categorized the smells emitted by four human volunteers, both before and after a wash with each of four brands of soap – Dial, Dove, Native and Simple Truth.

Unsurprisingly, each volunteers’ scent was unique, with some scent stamps proving more alluring to mosquitoes than others. After a soap scrub, these profiles rapidly changed – and not just by adding a floral hit as expected.

Chloé Lahondère, a co-author and biologist, added, “Soaps drastically change the way we smell, not only by adding chemicals, but also by causing variations in the emission of compounds that we are already naturally producing.”

The soaps that make mozzies hungry

Not all mosquitoes are bloodthirsty – far from it. Male mosquitoes gorge only on plant nectar, while females only get vampiric urges after mating. As a result, researchers only tested the attractiveness of post-coital female mosquitoes. Carbon dioxide exhaled by humans can also stimulate mosquitoes, so the team isolated these effects by analyzing fabric that had been exposed to the volunteers’ scent rather than the soaped-up people themselves.

The results were highly variable – Dove and Simple Truth made some (but not all) volunteers more appetizing to mosquitoes, while Native soap appeared to repel the insects.

“What really matters to the mosquito is not the most abundant chemical, but rather the specific associations and combinations of chemicals, not only from the soap, but also from our personal body odors,” says Vinauger. He pointed out that all of the soaps contained limonene, a known mosquito repellent. Yet, paradoxically, three out of the four soaps tested ended up increasing the mosquitoes’ attraction.

“We know that ratios of chemicals are extremely important for determining whether mosquitoes are attracted or repelled,” says Lahondère. “Changing the ratio of the same exact chemicals can result in attraction, indifference or repulsion.”

Bourbon chemical puts mosquitoes off

A deeper dive into the soaps’ chemicals in the context of their effect on mosquito attraction found four chemicals that made mosquitoes hungry for blood and three that fended them off. The repellant chemicals included a floral compound that can treat lice and scabies, and a coconut-scented molecule that can also be found in bourbon. By combining these chemicals together, the team could create strong pro- and anti-mosquito cocktails.

“With these mixtures, we eliminated all the noise in the signal by only including those chemicals that the statistics were telling us are important for attraction or repulsion,” says Vinauger. “I would choose a coconut-scented soap if I wanted to reduce mosquito attraction.”

Future studies from the team will look to expand their findings with more soaps and people, while exploring other variables. “We're very curious to look at the time course of this effect – so for example, if you take a shower in the morning, does it still matter to mosquitoes in the evening?” Vinauger concluded.

Reference: VanderGiessen M, Tallon AK, Damico B, Lahondère C and Vinauger C. Soap application alters mosquito-host interactions. iScience. 2023. doi: 10.1016/j.isci.2023.106667.

This article is a rework of a press release issued by Cell Press. Material has been edited for length and content.