Some people can sit outside all summer and not suffer from painful and annoying mosquito bites. Others become the focus of bites despite smearing themselves to the top with anti-mosquito protection. Why is this happening?
The key is in the invisible chemical landscape of the air around us. Mosquitoes take advantage of the environment through specialized behaviors and effective sensory organs to find victims by following the subtle chemical trails left by our bodies.
In particular, mosquitoes depend on carbon dioxide to find their hosts. When we exhale, the carbon dioxide in our lungs does not immediately mix with the air. It temporarily remains in tufts that mosquitoes follow like breadcrumbs.
“Mosquitoes begin to orient themselves towards these pulses of carbon dioxide and continue to fly against the wind while sensing concentrations higher than those contained in normal ambient air,” says Joop van Loon, an entomologist at Wageningen University in the Netherlands.
A human being produces approximately one kilogram of CO2 each day, and each time he exhales, approximately 13 times per minute, he emits more than one hundred milligrams of this gas. Mosquitoes detect the current with pulsations of CO2, which varies both between adults (more carbon dioxide when breathing) and children (less carbon dioxide when breathing) and depending on diet and physical exercise.
The lactic acid that we emit when we breathe or through sweat also attracts these insects . Taller people and pregnant women emit more lactic acid and CO2, making them perfect “targets” for mosquitoes. People who have just done strenuous exercise are also very attractive to insects.
Things get serious when mosquitoes are within about a meter of a group of possible targets. In confined spaces, mosquitoes take into account many factors that vary from person to person, such as skin temperature, the presence of water vapor, and color.
Scientists believe that the most important variable that mosquitoes rely on when choosing one person over another are the chemical compounds produced by colonies of microbes that live on our skin.
These chemical packages are complex, including more than 300 different compounds, and vary from person to person based on genetic variation and environment, as we say.
For example, men with a greater diversity of microbes on their skin tend to have fewer mosquito bites than men with fewer microbes on their skin, according to a 2011 study in the journal PLOS ONE. Additionally, the researchers found that men with less diverse microbes tended to have the following bacteria in their bodies: Leptotrichia, Delftia, Actinobacteria Gp3, and Staphylococcus.
In contrast, one study found that men with a wide variety of microbes tended to have Pseudomonas and Variovorax bacteria on their skin.
Subtle differences in the composition of this chemical cocktail can explain the large variations in the number of bites or stings a person receives . The composition of these microbial colonies can also vary over time in the same individual, particularly if that person is ill.
