Why some people are mosquito magnets might be due to which soap they use in the shower, according to new research, as the pesky insects fly towards or away from specific aromas.
“It’s remarkable the same individual that is extremely attractive to mosquitoes when they are unwashed can be turned even more attractive to mosquitoes with one soap,” said senior author Dr. Clement Vinauger. “Then, they become repellent or repulsive to mosquitoes with another soap.”
The results of the team’s experiments found that washing with Dove and Simple Truth increased the attractiveness of some of the volunteers, while the smell of the Native brand tended to deter the blood suckers, according to the team at Virginia Tech.
Commenting on the many theories for why some people attract mosquitoes while others get off bite-free, co-author Dr. Chloe Lahondere says it’s not easy to pinpoint a specific reason.
“Everybody smells different, even after the application of soap. Your physiological status, the way you live, what you eat, and the places you go all affect the way you smell.
“And 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.”
A series of experiments found soaps did impact mosquitoes’ preferences. Chemicals emitted by four human volunteers were analyzed both before and an hour after they’d applied body washes by Dial, Dove, Native, and Simple Truth (see the specific types below). Odor profiles of the soaps themselves were also broken down by chemical.
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Each participant emitted their own unique odor, some of which were more attractive to mosquitoes than others. Soap-washing significantly changed these—and not only by adding floral fragrances to the mix.
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Effects of exhaled carbon dioxide (CO2), another important cue for mosquitoes, were excluded by conducting tests on fabric that had absorbed the participants’ odors.
Humans can’t smell CO2, which we and other animals exhale with each breath. Mosquitoes can. It boosts females’ activity, making them explore surrounding space in search of a host.
“All of the soaps contained a chemical called limonene which is a known mosquito repellent but in spite of that being the main chemical in all four soaps, three out of the four soaps we tested increased mosquitoes’ attraction,” said Dr. Vinauger.
The study published in iScience identified four chemicals associated with mosquito attraction. Three chemicals repulsed the mosquito, including a coconut-scent in American Bourbon and a floral compound used to treat scabies and lice.
The two soaps advertised as more “natural” (Simple Truth and Native) tended to be less chemical-heavy soaps (e.g., lower abundance of saturated and unsaturated hydrocarbons, such as alkanes and alkenes) than Dial and Dove.
Four body washes were selected based on their brand popularity, and fragrance: 1) Dial Body Wash with Marula Oil, 2) Dove Deep Moisture Nourishing Body Wash 3) Simple Truth Organic Honey Blossom Baby Shampoo & Body Wash, and 4) Native Coconut and Vanilla Body wash.
They were combined to create and test attractive and repellent odor blends, which had strong impacts on the preference of the insects from the Aedes aegypti species.
“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,” said Vinauger.
However, the effect of soap applications on the proportion of landing observed was a function of the interaction between the soap and the volunteer. Specifically, fewer mosquitoes landed on either sleeve when volunteer 1 was washed with either Dial, Simple Truth, or Native soap, than when only their unwashed scent was presented.
“I would choose a coconut-scented soap if I wanted to reduce mosquito attraction.”
He now plans to expand the results and find some general patterns or rules by testing more soap varieties and many more people—and explore how soap impacts mosquito preference over a longer period of time.
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“We’re very curious to look at the time course of the effect… if you take a shower in the morning, does it still matter to mosquitoes in the evening?”
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