It is not just an urban myth: some people really are more prone to mosquito bites than others, a new study has found.
With mosquito season upon us in France, we explore how to avoid the worst of it.
The study by the Johns Hopkins University in the US looked into mosquito behaviour, particularly with a view to the situation in Africa, where mosquitoes cause the deaths of 400,000 people a year as a result of their spread of malaria.
The researchers constructed a giant ‘mosquito arena’ in Zambia and filled it with 200 female mosquitoes (the males do not bite). The species were Anopheles gambiae, which often carry malaria (although there are 3,600 species of the insect overall).
Six tents were installed around the arena, with a pipe connecting them to it. A volunteer spent six nights in each tent, in research conditions. Each volunteer and tent was equipped with tools to monitor their average skin temperature and other factors, and an infrared camera counted the number of mosquitoes in the tent.
The goal was to identify which person would attract the most mosquitoes into their tent, and why.
Some more attractive to mosquitoes than others
Researchers discovered 40 relevant chemicals over the course of the study - the results of which were published in the scientific journal Current Biology.
They found that one of the participants was much more likely than the others to attract the insects, with as many as 160 of the 200 mosquitoes recorded in their tent at once (compared to just a few dozen in others).
Risk factors: Diet, health, hygiene
The main reason behind it? Carboxylic acid levels, which are partly linked to a person’s diet. Carboxylic acids are molecules secreted by bacteria on the skin.
The volunteer attracting the most mosquitoes emitted the highest amount of these acids
The least-targeted volunteer emitted relatively few carboxylic acids, but three times more eucalyptol, synonymous with a diet rich in plants.
Didier Fontenille, director of research at the Institut de recherche pour le développement (IRD), said: “Our smell is in fact related to what we eat.”
But researchers say it also depends on:
Bacteria on our skin
The state of our health
The study found that other risk factors include:
Not washing your feet before bed. Unwashed feet have more bacteria and therefore attract more mosquitoes.
Pregnancy. Pregnant women are also more likely than average to be bitten.
Conor McMeniman, assistant professor at Johns Hopkins Bloomberg School of Public Health and Johns Hopkins Malaria Research Institute and senior author of the study, commented: “These mosquitoes typically hunt humans in the hours before and after midnight.
“They follow scent trails…emanating from humans, and typically they’ll…bite between around 22:00 and 02:00.
“We wanted to assess mosquito olfactory preferences during the peak period of activity when they're out and about and active, and also assess the odour from sleeping humans during that same time window.”
He continued: “We don’t really know yet exactly what aspect of skin secretions, microbial metabolites, or breath emissions are really driving this, but we’re hoping we’ll be able to figure that out in the coming years.”
Dr McMeniman added that in future years, further research could help to develop mass traps using imitation human odour to capture mosquitoes and reduce the incidence of malaria. The same idea could also help to create more effective repellents.
However, Anna-Bella Failloux, mosquito specialist at the Institut Pasteur, told Le Figaro that “the results are only valid for [this species of mosquito], so we can’t generalise the findings across the 3,600 species that we know of”.
But Dr Fontenille said that the study was “very robust and rigorous”.
Mosquitoes in France
The study comes as mosquitoes, and especially tiger mosquitoes, are becoming more prevalent in France.
The main concern about tiger mosquitoes is that they can carry several severe diseases, including dengue fever, zika, and chikungunya. These diseases are usually not associated with France and used to only affect people who had travelled to an at-risk area.
However, more cases of ‘native’ dengue have recently been reported.
In July 2022, five native cases of dengue were detected in the Provence-Alpes-Côte d'Azur (PACA) and Occitanie regions. A ‘native’ or ‘indigenous’ case means that it was identified in people who had not previously travelled to an international at-risk area, and the infection came from a tiger mosquito already within France.
This has led to the health authority la Direction générale de la santé (DGS) warning health professionals and the public to be alert to the increased risk.
How can you stop mosquitoes from spreading?
France’s health ministry said: “Prevention of bites and fighting the spread of mosquitoes is essential to limit epidemics.”
The main way to stop them from spreading is to remove any containers or areas of stagnant water in your garden or outside space, as this is where the mosquitoes lay their eggs.
You are advised to empty:
Plastic outdoor containers
Flower pot stands
Tools and other gardening items after rain (or store them away beforehand)
Any other areas of standing water
Showering or washing before you go to sleep, and using insect repellent in your sleeping area, can also keep them away.