Humans smell. Each and every person has a unique body odor.
People have been using commercial products to alter their scent for generations. From soaps to perfumes, people gravitate to floral and fruity smells.
Whether we think these smells are good or bad is of little consequence to mosquitoes, transmitters of diseases that kill hundreds of thousands of people each year. Additionally, mosquitoes rely on plant nectar to get some sugars needed to sustain their metabolism in addition to needing nutrients in the blood to produce eggs.
And humans with nutrients and a floral scent? That's two strikes.
In spite of these scents being right under humans' noses, the impact of soap smell on mosquito preference was largely ignored until Virginia Tech researchers in the College of Agriculture and Life Sciences asked this question.
And they found that certain soaps could make people more or less attractive to mosquitoes.
"Just by changing soap scents, someone who already attracts mosquitoes at a higher-than-average rate could further amplify or decrease that attraction," said Clément Vinauger, an assistant professor of biochemistry and co-principal investigator on the proof-of-concept study alongside his collaborator Chloé Lahondère, also an assistant professor of biochemistry.
The research on mosquito soap interactions was published on May 10, 2023, in iScience and was funded in part by the United States Department of Agriculture and the National Institute of Food and Agriculture.
Hidden under human noses
The connection between soap and mosquito attractiveness was studied through four volunteers. First, the research team, comprised of Morgen VanderGissen, graduate student, Anaïs Tallon, a postdoctoral associate, in addition to Lahondère and Vinauger, studied the unique scent profile of each individual, unwashed and washed with each Dial, Dove, Native, and Simple Truth soaps.
According to Vinauger, more than 60 percent of what is smelled after washing comes from soap, rather than natural body odors.
"The other aspect is that it's not simply adding stuff to our body odor, but it's also replacing some chemicals while eliminating others, that are washed away," Vinauger said. "So we think there is a lot of chemical interaction between our natural chemicals and soap chemicals."
To test the interactions between smell, the researchers released mosquitoes in a meshed cage that had two cups containing odor extracts and gave them a choice – unwashed scents gathered from the individuals along with their washed scents. These were gathered from a nylon sleeve on the forearm with the body in both washed and unwashed states. Tests were repeated for the various combinations of scents.
"This way we can really measure and quantify the effect of the soap in terms of increasing or decreasing the attractiveness of the individual," Vinauger said. "That's where we found that not all soaps have the same effect on all volunteers."
In terms of fragrance preferences, three of the four soaps increased mosquito attractiveness while one decreased. All of the soaps had a fruity or flowery scent. The one that decreased attractiveness was coconut scented.
"That was very interesting for us because there is other evidence in the literature that elevating certain fatty acids, such as those found in coconut oil derivatives, could serve as a repellant for mosquitoes and other insects," Vinauger said.
Odors are everywhere
With the results of the proof-of-concept study in hand, the research team hopes to expand the study with additional people and soap varieties to get a clearer understanding of the implications.
"Trying different soaps is important because we are showing that it's really the combination between your natural odor and a specific soap that matters," Vinauger said. "We also need to study the duration of these effects. What if you shower in the morning? The evening? We need to answer these questions in our future work."
Soap is only one part of the equation. Deodorants, laundry detergents, and other scented products could also play a factor.
While there is more work to be done, research shows that using coconut-scented soaps could reduce attractiveness to mosquitoes.
