Why Mosquitoes Bite Some People More Than Others

About 1 in 5 people are, in the words of researchers who study this, especially delicious to mosquitoes. They get bitten more, and they get bitten consistently — not just on unlucky nights.

That's not folk wisdom. It's the starting point for a real research question, because mosquitoes don't bite at random and the difference matters for more than comfort. Mosquitoes spread malaria, dengue and Zika, and understanding who they target is a piece of controlling those diseases. Smithsonian magazine's rundown of the research lists roughly 250 million malaria cases worldwide in 2022, leading to more than 600,000 deaths.

The blood type link is real, but modest

Start with the claim you've probably heard: mosquitoes prefer Type O blood. It checks out, with caveats. A 1974 study of 102 participants found mosquitoes preferentially fed on people with Type O blood. A 2019 study offering mosquitoes separate feeders for each blood type found they went to the Type O feeder most often. A 2004 study found something more specific: mosquitoes landed on Type O people significantly more than Type A people, but the difference against Type B wasn't statistically significant.

The blood type itself may not be the real signal. About 85% of people are "secretors" — they release chemical markers of their blood type through skin, saliva and tears, not just in their blood. The other 15% don't secrete these markers at all. In the 2004 study, mosquitoes were drawn to Type O secretors far more than Type A secretors, and were more attracted to secretors generally, regardless of type. That suggests mosquitoes may be reading a chemical signal on the skin, not detecting blood type directly.

What mosquitoes are actually sensing

Blood type turns out to be one input among several, and the mechanical ones are better understood.

Carbon dioxide is the long-range signal. Mosquitoes sense it through an organ called the maxillary palp and can detect it from as far as 100 feet away. People who simply exhale more CO2 over time draw more mosquitoes at medium and long range — before the insect ever gets close enough to smell skin.

Once nearer, mosquitoes switch to smell and heat. Sweat carries lactic acid and ammonia, both linked to increased attraction, and strenuous exercise raises both — meaning a hard run can make you a better target than sitting still. Mosquitoes are also drawn to warmer body temperatures; when researchers disabled a heat-sensing "thermostat" molecule in mosquito antennae in a study published in the journal Science in 2020, the insects lost much of their ability to detect body heat and fed less.

Skin bacteria matter too, in an unintuitive way. A 2011 study found people carrying large amounts of just a few bacterial species were more attractive to mosquitoes — but people whose skin hosted a greater diversity of bacteria were less attractive, even with similar overall bacterial loads. Researchers think this may help explain why ankles and feet, where certain odor-producing bacteria concentrate, draw so many bites.

Taste, beer, and one genuine scientific mystery

The newest piece of the picture comes from Yale, where researchers led by biologist John Carlson published findings in 2024 showing that different compounds in human sweat push mosquito behavior in opposite directions: some increase biting, others — bitter compounds — suppress it. Combinations mattered in ways single compounds didn't; certain amino acids and salt didn't change biting when tested alone, but did when combined, which matches how those compounds actually sit together on real skin.

"We think this could be part of the reason why some of us get bitten by mosquitoes a lot more than others. Some people may just taste better to mosquitoes."

John Carlson, Yale University biologist

Then there's the one factor nobody has a mechanism for: beer. A 2010 study found that drinking just a liter of beer made people more attractive to mosquitoes. Researchers checked whether it worked through elevated CO2 or body temperature, the two usual suspects — and found neither one correlated with the increased attention. The link is real in the data. Why it happens remains, in the researchers' own framing, "something of a mystery."

Pregnancy adds a documented, physiological push in one direction. Multiple studies have found that pregnant women attract roughly twice as many bites from malaria-carrying mosquito species as non-pregnant women in the same setting — plausibly because pregnant women exhale about 21% more carbon dioxide and run roughly 1.26 degrees Fahrenheit warmer around the belly.

What you can actually do about it

Genetics sits underneath most of this. Researchers describe underlying genetic factors as a key driver of mosquito attractiveness regardless of whether it shows up as blood type, metabolism, or body odor — and a 2015 study found a genetic basis for some of the specific odors mosquitoes respond to. That's not something a bug spray changes.

What does change the odds is repellent choice, and here the evidence is unusually clean. Comparison studies from 2015 and 2017 found that repellents containing DEET were consistently the most effective at deterring mosquitoes among commercially available products, ahead of picaridin, IR3535, oil of lemon eucalyptus and the clove-derived compound 2-undecanone — all of which are approved by the Environmental Protection Agency as safe and effective active ingredients. Avoiding dawn and dusk, when mosquitoes are most active, and clearing standing water where they breed, round out the practical list.

None of it will turn a genetic magnet into someone mosquitoes ignore. But for the 1 in 5 who already know which category they're in, it's the difference between a repellent that's doing real work and one that's mostly a ritual.