Mosquitoes are drawn to a specific cocktail of smells that your body produces naturally, starting with the carbon dioxide you exhale. They can detect CO2 from more than 30 feet away, and that initial whiff kicks off a chain of sensory responses that guide them closer to your skin. But CO2 is just the opening signal. The scents that truly seal the deal come from your skin chemistry, the bacteria living on your body, and even the soap you use.
Carbon Dioxide: The Long-Range Signal
Every breath you exhale sends a plume of CO2 into the air, and mosquitoes pick up on it from remarkable distances. This is the first smell they detect, and it does more than just alert them to a nearby host. Research at the University of Washington found that when mosquitoes smell CO2, it literally activates their visual system, prompting them to scan for dark-colored objects like skin and clothing. Mosquitoes that had the CO2-sensing gene knocked out showed no interest in visual targets at all. So the smell of your breath is what flips the switch from passive hovering to active hunting.
This is one reason pregnant women get bitten more often. They exhale about 21% more CO2 than non-pregnant women, effectively broadcasting a stronger signal. Anyone with a higher metabolic rate, whether from exercise, larger body size, or pregnancy, puts out more CO2 and becomes easier to find.
Skin Chemistry: What Makes You Smell “Human”
Once a mosquito gets within a few feet of you, it shifts from tracking CO2 to reading the chemical signature of your skin. Your body releases hundreds of volatile compounds through sweat and skin oils, and mosquitoes have specialized receptors on their antennae, near their mouths, and on their feeding tube to sort through them. NIH-funded research found that different combinations of these scent receptors light up different regions of the mosquito brain depending on whether the smell comes from a human, a rat, a dog, or even a flower. Mosquitoes don’t just smell “warm body.” They can distinguish human from animal.
The compounds that matter most are carboxylic acids, a type of fatty acid found on the skin’s surface. NIH researchers using mass spectrometry found that the people mosquitoes liked best had significantly higher concentrations of carboxylic acids on their skin. Lactic acid, a well-known component of sweat, is another major attractant. When scientists used gene editing to disable a specific smell receptor called Ir8a in mosquitoes, the modified insects completely lost their attraction to lactic acid and showed dramatically reduced interest in human odor overall. The CO2 detection system alone wasn’t enough to guide them to people; they needed this secondary scent pathway too.
Skin Bacteria: Why Feet Are a Hotspot
The smell mosquitoes follow isn’t just what your sweat glands produce. It’s also what the bacteria on your skin produce as they break down those secretions. A study published in PLOS ONE found that people who attracted the most mosquitoes had a higher total number of bacteria on their skin but lower diversity. In other words, having a few dominant bacterial types creating a strong, consistent odor was more attractive than having a complex mix of many species.
Specifically, people who were highly attractive to mosquitoes had 2.6 times more Staphylococcus bacteria on their skin compared to people mosquitoes avoided. Meanwhile, less attractive individuals had about three times more Pseudomonas bacteria. The researchers found a direct correlation between the number of bacteria per square centimeter on the sole of a person’s foot and how attractive that person was to mosquitoes. This explains why some mosquito species famously target ankles and feet: the bacterial colonies there produce a concentrated bouquet of volatile compounds that mosquitoes find irresistible.
How Soap Changes Your Scent Profile
Here’s something most people don’t consider: after you wash with scented soap, more than 60% of what mosquitoes smell on you comes from the soap, not your natural body odor. A Virginia Tech study tested four popular soaps and found that three of them, all with fruity or floral scents, increased mosquito attraction. Only one decreased it: a coconut-scented soap.
The researchers believe fatty acids found in coconut oil derivatives may act as a natural repellent. This means your choice of soap can either amplify or reduce your attractiveness to mosquitoes, sometimes enough to override your baseline scent profile. Someone who naturally attracts a lot of bites could make it worse with a floral body wash or better with a coconut-based one.
Alcohol, Body Heat, and Other Amplifiers
Drinking beer makes you more attractive to mosquitoes, but not for the reasons you’d expect. A study on beer consumption and mosquito attraction ruled out the two most obvious explanations: body temperature and CO2 output. Beer drinkers actually had slightly lower body temperatures after drinking, and their CO2 levels didn’t change. The researchers concluded that alcohol metabolism alters the volatile compounds in your breath and skin odor, likely increasing production of specific chemicals that mosquitoes use to locate hosts.
Body heat does play a role at very close range. Mosquitoes can sense the infrared radiation from your skin from about two and a half feet away while in flight, and traditional heat sensing through warm air works within about four inches. This thermal detection is most effective when the surrounding air is cooler than skin temperature. In the heat of midday, when ambient temperatures match skin temperature, mosquitoes lose this advantage, which partly explains why biting peaks at dawn and dusk.
Blood Type and Genetic Factors
You may have heard that mosquitoes prefer type O blood, and there is some evidence for this. One study found mosquitoes landed more frequently on people with type O blood compared to type A. But the picture is more nuanced than headlines suggest. About 85% of people secrete chemical signals through their skin that advertise their blood type, giving mosquitoes something to detect before they ever bite. The remaining 15% who don’t secrete these signals may get some protection regardless of blood type.
That said, researchers caution against reading too much into blood type studies. In any comparison, one group will come out ahead, and the differences between blood types are modest compared to the effects of skin chemistry, bacterial composition, and metabolic rate. Your overall scent profile matters far more than your blood type alone.
What Mosquitoes Ignore or Avoid
Mosquitoes are surprisingly selective. After detecting CO2, they fly toward red, orange, and black visual targets but completely ignore green, blue, and purple. This preference only activates after they’ve smelled CO2, meaning color alone doesn’t attract them. On the scent side, coconut-derived compounds and certain bacterial profiles (particularly those with high microbial diversity) seem to reduce interest. The mosquito’s olfactory system has evolved to home in on a very specific combination of human chemical signals, and anything that disrupts or masks that combination can make you less detectable.