Why some people are bitten by mosquitoes more often than others

It is not "sweet blood" or eye colour that plays the main role, but a combination of signals: the carbon dioxide we exhale, skin odour, body temperature, humidity and the chemicals that are produced on the skin by the microbiota.

Details

Only female mosquitoes bite humans: they need blood to reproduce. First, mosquitoes pick up the carbon dioxide that humans exhale. This signal can attract them from dozens of metres away. Then, as they get closer, they begin to orientate themselves by body odour, and in close proximity - by the warmth and moisture of the skin.

Odour is particularly important. Human skin emits hundreds of volatile compounds, and their set is different for everyone. This "chemical cocktail" is influenced by sebum, sweat, bacteria on the skin, physiological state and human behaviour.

In a recent study, scientists examined how female Aedes aegypti mosquitoes select humans. Forty-two females participated in the experiment. The researchers found that pregnancy and menstrual cycle phase influenced attractiveness to mosquitoes, and chemical analysis of body odours revealed 27 volatile organic compounds that may be linked to how attractive humans are to insects.

One of these substances was 1-octen-3-ol, also called "mushroom alcohol." It is formed by the breakdown of sebum components and can increase a person's attractiveness to mosquitoes.

The popular theory that mosquitoes select people based on blood type remains controversial. There have been some small studies on this topic, but there is no stable and convincing scientific basis for the simple conclusion "mosquitoes like this blood type".

The role of odour, carbon dioxide, heat and skin chemistry is much more reliably confirmed. So the "my blood tastes good" explanation sounds spectacular, but is scientifically weaker than the odour and microbiota version.

There is evidence that drinking beer can make humans more attractive to mosquitoes. In a study at a festival in the Netherlands, volunteers placed their hands in special cages with female Anopheles mosquitoes. People who had drunk beer in the previous 24 hours were about 1.35 times more attractive to the insects.

Scientists don't think that mosquitoes "like alcohol" per se. More likely, it is a matter of changes in skin odour, body temperature, exhaled CO₂ or other physiological signals. So giving up beer does not guarantee complete protection, but alcohol may be one of the factors that increase the risk of bites.

Why it matters

Mosquitoes aren't just nuisance insects. Some species carry dangerous infections including dengue, yellow fever, malaria, chikungunya, and the Zika virus. Understanding why mosquitoes choose some people more often can help create more effective traps, repellents and defence methods.

This becomes particularly relevant against the backdrop of climate change: the ranges of some mosquito species are expanding, and diseases that used to be common in warmer regions are appearing further north.

Mosquitoes cannot completely "stop liking" mosquitoes, but the risk can be reduced. The safest measures are to use repellents, wear loose, closed clothing, protect windows and sleeping areas with mosquito nets, and avoid leaving standing water near your home where mosquitoes breed. The CDC also recommends using registered repellents and covering your skin with clothing, especially in areas where mosquitoes are abundant.

Background

Previously, researchers from Rockefeller University have also shown that some people persistently remain "magnets" for mosquitoes because of the composition of their skin odours. Specifically, they linked attractiveness to increased levels of carboxylic acids, which are formed on the skin and can be influenced by the microbiota.

But there is no universal single factor. The mosquito does not focus on a single trait, but on a combination of signals. Therefore, two people next to each other can receive different numbers of bites even with similar clothing, diet and conditions.

Source

Material AFP Why are some people mosquito magnets? Clues are emerging on Phys.org summarises new data on how mosquitoes choose people. It is based on studies of skin odours, carbon dioxide, body temperature, microbiota and behavioural factors including beer consumption. Additional data are published in Cyphers and cycles - a chemical basis for the differential attraction of humans to Aedes aegypti, which examined the attractiveness of 42 women to Aedes aegypti mosquitoes.