Can scented soap make you less of a mosquito buffet?

Unfortunately, vitamins and supplements won’t stop mosquitoes from biting you this summer, but scientists are still trying to figure out why insects love to suck blood more than others.

[Related: How can we control mosquitos? Deactivate their sperm.]

In a small study published May 10 in the journal iScience, a team of researchers analyzed the possible effects that soap has on mosquitoes. While some soaps seemed to repel insects and others to attract them, the effects varied greatly depending on how the soap interacted with an individual’s unique odor profile.

“It is remarkable that the same individual that is extremely attractive to mosquitoes when not washed can be made even more attractive to mosquitoes with one soap and then made repellent or repulsive to mosquitoes with another soap,” said co-author and Virginia neuroethologist Tech, Clement. Vinauger said in a statement.

Soaps and other odor-reducing products have been used for millennia, and while we know they change our perception of another person’s natural body odor, it’s less clear if soap also works this way for mosquitoes. Since mosquitoes feed primarily on plant nectar and not just animal blood, using plant-mimicking or plant-derived scents can confuse your decision-making about what to feast on next.

In the study, the team began by characterizing the chemical odors emitted by four human volunteers when they had not washed and then washed with four common brands of soap (Dial, Dove, Native, and Simple Truth). The odor profiles of the soaps themselves were also characterized.

They found that each of the volunteers emitted their own unique odor profile, and some of those odor profiles were more attractive to mosquitoes than others. The soap changed the scent profiles significantly, not just adding some floral fragrances.

“Everyone smells different, even after applying soap; Your physiological state, the way you live, what you eat and the places you go all affect the way you smell,” co-author and Virginia Tech biologist Chloé Lahondère said in a statement. “And soaps drastically change the way we smell, not just by adding chemicals, but also by causing variations in the emission of compounds we already produce naturally.”

The researchers then compared the relative attractiveness of each human volunteer, unwashed and one hour after using the four soaps, to Aedes aegypti mosquitoes These mosquitoes are known to spread yellow fever, malaria, and Zika, among other diseases. After mating, male mosquitoes feed mainly on nectar and females feed exclusively on blood, so the team exclusively tested attractiveness with recently mated adult female mosquitoes. They also eliminated the effects of exhaled carbon dioxide by using fabrics that had absorbed the odors of humans rather than the humans themselves breathing.

[Related from PopSci+: Can a bold new plan to stop mosquitoes catch on?]

They found that soap washing affected mosquito preferences, but the size and direction of this impact varied between types of soap and humans. Washing with Dove and Simple Truth increased the attractiveness of some, but not all of the volunteers, and washing with native soap tended to repel mosquitoes.

Graphical summary showing how soaps alter the olfactory signature of human hosts, thereby affecting their attractiveness to mosquitoes. CREDIT: VanderGiessen et al.

“What the mosquito really cares about is not the most abundant chemical, but the specific associations and combinations of chemicals, not just from soap, but also from our personal body odors,” Vinauger said. “All the soaps contained a chemical called limonene, which is a known mosquito repellent, but even though that is the main chemical in all four soaps, three of the four soaps we tested increased the attraction of mosquitoes.”

To take a closer look at specific soap ingredients that might attract or repel insects, they analyzed the chemical compositions of the soaps. They identified four chemicals associated with mosquito attraction and three chemicals associated with repulsion. Two of the mosquito repellents are a coconut-scented chemical that’s a key component in American bourbon, and a floral compound used to treat scabies and lice. They combined these chemicals to test mixtures of attractive and repellent odors, and this mixture had a strong impact on mosquito preference.

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

The team hopes to test these results using more varieties of soap and more people, and to explore how soap affects mosquito preference over a longer period of time.

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