Why mosquitoes bite some people more than others - Maria Elena De Obaldia

Some swear they’re cursed to be hunted by mosquitoes while their close-by companions are regularly left unscathed.

But is this an illusion?

If it's not, what's going on? And what can we do about it?

It all comes down to how— and why— mosquitoes find us.

While male mosquitoes stick to nectar for sustenance, females also seek out blood to provide the nutrients they need for their eggs.

Different mosquito species evolved to feed on different animals.

And, probably within the last 10,000 years, multiple mosquito lineages independently evolved a predilection for people.

As human settlements became more permanent, they provided plenty of standing water, even through intense dry seasons, which supported mosquito reproduction year-round.

Female mosquitoes are equipped with antennae covered in hair-like appendages that contain odor-sensing receptors and neurons.

These pick up on the signals of their preferred hosts, And over thousands of years, the mosquitoes that target humans have gotten extremely good at tracking us down.

They also target parts of our bodies where we’re less likely to notice them.

And they’re sensitive to visual cues and changes in airflow, so when we try to defend ourselves, they can make swift escapes.

They even learn to avoid particularly defensive people altogether.

But before these close encounters happen, several factors alert mosquitoes to people's presence.

Female mosquitoes can pick up on the carbon dioxide humans constantly exhale from about 10 meters away.

Once they’ve gotten the CO2 cue, they become especially interested in dark, high-contrast objects and the hues found in human skin.

As they follow the carbon dioxide plume to its source, they eventually sense body heat and odors.

These smells are generated by the many microorganisms that live on our skin.

They break down the secretions our bodies produce, like sweat and sebum.

In doing so, our skin microbes create smaller organic compounds that can vaporize and get picked up as smells— smells that human-homing mosquitoes are especially attuned to.

Getting extra sweaty can temporarily make people more attractive to mosquitoes— as can ingesting alcohol or being pregnant.

And the Plasmodium parasite that causes malaria makes the people it infects more appealing to mosquitoes by increasing the amounts of certain fruit-smelling aldehyde compounds on their skin.

This is extremely helpful to the parasite because it depends on both humans and mosquitoes to reproduce.

But in addition to these temporary factors, about 20% of people are thought to be naturally high attractors, or mosquito magnets, who are disproportionately targeted year after year.

If you’re one of them, you’re probably well aware.

Sorry about that.

Why this is seems to come down to some skin-specific characteristics.

While carbon dioxide exhalations and body heat consistently signal the presence of warm-blooded animals, human body odor is more distinctive.

And everyone hosts different microbial communities on their skin, which contribute to unique body odors that likewise vary from person to person.

Researchers reveal that the receptors mosquitoes use to detect acidic compounds are especially important in helping them navigate towards humans.

And, indeed, humans with more abundant skin acids prove to be consistently more attractive to mosquitoes.

Because it’s such a persistent trait, certain genes may play a role, perhaps by helping determine the skin’s microbial composition.

Scientists have observed that mosquitoes demonstrate similar levels of attraction among identical twins while responding more variably to fraternal twins, which supports that there may be some genetic basis at play.

But beyond confirming that mosquitoes are, in fact, conspiring against some of us specifically, understanding what makes people mosquito-magnets has serious, large-scale implications.

Every year, hundreds of thousands of people die from mosquito-borne diseases.

And resources aren’t reaching those who need them most.

This knowledge can help inspire solutions, like more effective insect repellents that manipulate the skin's microbiome and odors.

And knowing that some people are especially strong mosquito attractors could also help efforts to get them resources like repellents, bed nets, vaccines, tests, and treatments.

The results could not only be less itchy, they could break transmission cycles and save countless lives.