The mosquitoes are out. Everywhere in France, voracious insects disturb the first desires for barbecue. This is the moment researchers at the Polytechnic Institute and State University of Virginia – known as Virginia Tech – have chosen to tell us some bad news: most of the scented soaps we use boost the appetite of laying females – since they, and only them, bite.
Assistant professor in the American university and coordinator of the study, the Frenchman Clément Vinauger explains the mechanism, described in the review iScience from May 10: “Female mosquitoes need blood to obtain the proteins necessary for egg production. But females, like males, also need sugars from plants to get the energy they need for their metabolism. To find these resources, they use volatile compounds emitted by them. But what differentiates us from other animals is that, every day, we use cosmetic or hygiene products, such as soaps, and apply them to our skin. » Products intended to flatter our nostrils, often exhaling sweet vegetable scents. “From the perspective of mosquitoes, therefore, we are a resource that smells like both an animal and a plantcontinues the researcher. However, the effect of adding these plant-emitted compounds to our body odor on mosquito response had never been tested. »
To undertake this study, the team he leads with the French Chloé Lahondère used methods that the researcher qualifies as“pretty conventional”. Four volunteers were recruited to successively test the four main soaps sold in the United States: Dial, Dove, Simple Truth and Native (in France, Dove is the only one marketed). Each time, they were asked to wash one of the two arms, to simply rinse the other, then to wear nylon sleeves for an hour so that the fabric was impregnated with the smell emitted: that of body on one side, body and soap on the other. All that remained was to study the two pieces of fabric for each volunteer, an operation repeated for several months.
Chemical analysis using a mass spectrograph made it possible to determine the compounds emitted. And there, the first remarkable result: while human body odor is made up of 80% aldehydes, ketones, carboxylic acids and alcohol, “what you smell after washing comes over 50% from soap and is largely dominated by a chemical class called terpenes, which are typically produced by plants”says Clément Vinauger.