Bug off! Your scent signature could be key to keeping mosquitoes away
Two new studies analyzed the effects of human body odour, soap scents on mosquitoes
It's the million-dollar question that comes around every summer: What's the best way to keep bloodsucking mosquitoes away? The results from two new studies are getting us closer to that answer in ways that better reflect what happens in natural settings.
It turns out that what distinguishes a mosquito magnet from a repellent is their personal scent signature — a mix of chemicals influenced by exercise, the cosmetic products we use and maybe even our diets.
"By identifying chemicals found in the scent signatures of least-preferred humans, perhaps we could use those chemicals to potentiate [or strengthen] the effects of existing insect repellents," researcher Conor McMeniman told Quirks & Quarks host Bob McDonald.
McMeniman, who is an assistant professor of molecular microbiology and immunology at Johns Hopkins Bloomberg School of Public Health in the Malaria Research Institute, said the goal of his study was to create a setting to hone in on specific scents that night-hunting, malaria-carrying mosquitoes in Africa prefer in their sleeping blood meals.
"I like to think of this as the largest perfumery for mosquitoes in the world," he said.
Most of what we know about mosquito behaviour comes from laboratory settings, without a lot of consideration for how the human bouquet of aromas can change throughout the day. That's why McMeniman's team built an ice rink-sized enclosure in Zambia, about 2,000 times larger than a typical lab wind tunnel where scientists normally test mosquitoes' scent preferences.
Researchers set up the enclosure much like a blind taste test: they placed single-person tents outside the enclosure and used refurbished air conditioning ducting to pipe the odours from each sleeping individual onto a hot plate warmed to the temperature of human skin. The mosquitoes would land on the hot plates with the most delicious scents.
As their test subjects dozed away, McMeniman said his team used night-vision cameras to watch, wait and document what happened over six consecutive nights.
"We were really excited to see that night after night, certain individuals seemed to be more attractive to mosquitoes," said McMeniman.
One individual in particular proved to be the clear preference for the African malaria mosquitoes. That person's scent profile contained a much higher abundance of carboxylic acids, which are metabolites produced by bacteria in our skin microbiomes and by glands in our skin that release an oily secretion to hydrate and protect our skin.
A different individual's smell was more of a natural repellent for the mosquitoes.
"Very strikingly, this individual had a body odour profile that was really different from the other individuals," added McMeniman.
That person's scent profile was nearly depleted of carboxylic acids, but was enriched with eucalyptol — a compound found in a variety of plants.
McMeniman hypothesizes the person's plant-based diet may have something to do with their vastly different scent signature. He says they hope to test that in future studies, along with how a person's microbiome may factor into it.
A mosquito soap opera
In a separate study, Virginia Tech researchers tested how washing with soap from four brands — Dial, Dove, Native, and Simple Truth — changed how alluring people were to mosquitoes.
The idea came to researcher Chloé Lahondère while studying how mosquitoes and plants interact at her lab at Virginia Tech.
"Not all species of mosquitoes are blood feeders. The males are only feeding on sugar sources, so they go for nectar, for fruits," Lahondère told Quirks & Quarks.
"Female mosquitoes feed on blood to mature the eggs that they are going to lay after. But they also need sugar sources for doing pretty much everything else."
Mosquitoes have a keen sense of smell they use to find plants — and people. But when we use cosmetic products with plant-derived chemicals, Lahondère said, we may be inadvertently adding more scents that are delectable to mosquitoes.
To see how the mosquitoes reacted to the soap scents, Lahondère and her team asked volunteers to wash one arm with one of the soaps and leave the other arm unwashed. They collected the scents from both arms using a special absorbent sleeve, which they presented to mosquitoes in a separate room.
Of the four soaps they tested, the mosquitoes were attracted to three of them, while the fourth acted as a repellent.
"Looking at the composition of that specific body wash, we found that it was made of coconut derivatives," which supports the existing evidence that coconut scents repel mosquitos, Lahondère said.
She cautions the same results may not apply to everyone.
"It is the combination of the host signature [scent] with the use of the soap that is going to drive either an aversion or an attraction," she said, explaining that the human's scent has a "huge impact" on the resulting combination.
So for those wishing to keep the mosquitoes away this summer, Lahondère recommends conducting your own experiments by trying out different soaps — but also to not forget other precautionary measures, like wearing light-coloured clothing with long sleeves and pants, and using bug spray.
Written and produced by Sonya Buyting and Olsy Sorokina.