Acids in our body odour make some people more attractive to mosquitoes

Some people may be more attractive to mosquitoes than others due to an acidic byproduct made by skin bacteria.

Maria Elena De Obaldia at the Rockefeller University in New York and her colleagues asked eight people to wear sleeves made from nylon for 6 hours.

In a series of experiments, nylon swatches worn by each individual were placed in one of two boxes, with the second box containing fabric worn by another of the participants.

A third box was attached via a tunnel to the two boxes. This box contained female Aedes aegypti mosquitoes, a major carrier of infections such as yellow fever and Zika.

By studying various fabric combinations, the researchers analysed which of the two boxes attracted more mosquitoes. They repeated the experiment over several months to determine if their findings were consistent.

The researchers found that nylon worn by people with high levels of carboxylic acids in their body odour was the most attractive to the insects, with these participants being called “mosquito magnets”. Bacteria on the skin produce carboxylic acids as a byproduct of another material produced by skin, called sebum.

De Obaldia notes that the team didn’t categorise every chemical in the participants’ body odours, which permeated the nylon. Other skin chemicals and factors such as body temperature and the exhalation of carbon dioxide have also been linked to mosquito-biting behaviour.

Unfortunately, it may not be possible to change the amount of carboxylic acids we produce in an attempt to avoid being bitten. “Human skin odour may be affected by genetic factors, skin microbiome and [our overall] diet,” says De Obaldia. “It is unlikely to be caused by short-term factors that are constantly changing, such as what one has for lunch on a particular day.”

Skin bacteria play a major role in our body odour. By living deep in the pores, the microbes can’t easily be removed, says De Obaldia. “Even when we wash the skin surface, it is soon repopulated by skin microbes.”

In a second part of the research, the team repeated the experiment with genetically modified mosquitoes that have a reduced ability to sense acids. A far lower percentage of these mosquitoes were attracted to the nylon, but the insects could still differentiate fabrics belonging to mosquito magnets.

“I think this reflects [the fact] that mosquitoes are choosing who to bite based on several – potentially many – odours emanating from our skin,” says De Obaldia. “It also reflects redundancy in the olfactory system of the mosquito: when one receptor pathway is disrupted, the relevant molecules can still be detected by a different receptor pathway.”

According to De Obaldia, it is unclear why mosquitoes are attracted to one human over another. “Female mosquitoes can get perfectly good blood protein to support egg development from any human,” she says.

“This is an important discovery that promises to trigger the development of new specific interventions such as genetically modifying mosquitoes to prevent them from biting people and transmit[ting] disease,” says George Christophides at Imperial College London.