Mosquitoes feast on us for practical reasons. Only the females bite humans and they do it to get a “blood meal,” deriving proteins from our blood to produce their eggs. To help locate their prey, female mosquitoes use their antennae and palps, the organs between their antennae, to detect carbon dioxide and odor. That means people who have a high metabolic rate and emit more carbon dioxide, including those who are pregnant, working out, or drinking alcohol tend to be more attractive to mosquitoes.

The question of whether mosquitoes prefer a certain blood type is controversial. One theory suggests that blood type may also help determine mosquito preference. If that’s the case, what blood type do mosquitoes like? A 2019 study found that the major mosquito vector of dengue virus preferred people with type O blood to those with other blood types.  However, separate research notes that experimental and laboratory data evaluating whether blood type makes one person more (or less) attractive to mosquitoes has fueled a lot of speculation, but the science is contradictory. Instead, the researchers report that the likelihood of being a “mosquito magnet” has more to do with skin odors and microbiota than blood type.

If you have the misfortune of being a mosquito magnet, it may just come down to your genetic makeup. A 2015 twins study published in the journal PLOS One found that DNA may account for nearly 67% of mosquito attraction similar to the levels at which height and IQ are considered genetically linked.

A mosquito bite might not seem like a big deal, but these tiny insects can be a deadly menace. Mosquitoes are vectors that can transmit infectious pathogens, including mosquito-borne diseases like dengue, Zika, chikungunya and West Nile fever. The World Health Organization (WHO) estimates that these kinds of vector-borne diseases are linked to more than 700,000 deaths annually, making mosquitoes among the deadliest animals on Earth.

We might not be able to understand the genetic factors that make you more attractive to mosquitoes, but we can still take steps to reduce your risk of mosquito bites.

Whether you are a mosquito magnet or just suffer the occasional bite, the Centers for Disease Control and Prevention recommends wearing shirts and long pants, especially fabrics treated with the insect repellant 0.5% permethrin, and applying insect repellents that contain ingredients like DEET or oil of lemon eucalyptus (OLE) and reapplying as directed.

We can also take steps to control mosquitoes indoors and outside by installing window screens and keeping doors closed, using air conditioning during the warmer months, and eliminating standing water in birdbaths, pools, buckets, and flower pots.

Blood Type

Not surprisingly—since mosquitoes bite us to harvest proteins from our blood—research shows that they find certain blood types more appetising than others. One study found that, in a controlled setting, mosquitoes landed on people with Type O blood nearly twice as often as on those with Type A.

People with Type B blood fell somewhere in the middle of this itchy spectrum. Additionally, based on other genes, about 85% of people secrete a chemical signal through their skin that indicates which blood type they have, while 15% do not, and mosquitoes are also more attracted to secretors than nonsecretors regardless of which type they are.

Carbon Dioxide

One of the key ways mosquitoes locate their targets is by smelling the carbon dioxide emitted in their breath—they use an organ called a maxillary palp to do this, and can detect carbon dioxide from as far as 164 feet away. As a result, people who simply exhale more of the gas over time—generally larger people —have been shown to attract more mosquitoes than others. This is one of the reasons why children get a bit less often than adults, on the whole.

Exercise and Metabolism

In addition to carbon dioxide, mosquitoes find victims at closer range by smelling the lactic acid, uric acid, ammonia and other substances expelled via their sweat, and are also attracted to people with higher body temperatures. Because strenuous exercise increases the buildup of lactic acid and heat in your body, it likely makes you stand out to the insects. Meanwhile, genetic factors influence the amount of uric acid and other substances naturally emitted by each person, making some people more easily found by mosquitos than others.

Skin Bacteria

Other research has suggested that the particular types and volume of bacteria that naturally live on human skin affect our attractiveness to mosquitoes. In a 2011 study, scientists found that having large amounts of a few types of bacteria made skin more appealing to mosquitoes. Surprisingly, though, having lots of bacteria but spread among a greater diversity of different species of bacteria seemed to make skin less attractive. This also might be why mosquitoes are especially prone to biting our ankles and feet; they naturally have more robust bacteria colonies.

Beer

Just a single 12-ounce bottle of beer can make you more attractive to the insects, one study found. But even though researchers had suspected this was because drinking increases the amount of ethanol excreted in sweat, or because it increases body temperature, neither of these factors were found to correlate with mosquito landings, making their affinity for drinkers something of a mystery.

Pregnancy

In several different studies, pregnant women have been found to attract roughly twice as many mosquito bites as others, likely a result of the unfortunate confluence of two factors: They exhale about 21% more carbon dioxide and are on average about 1.26 degrees Fahrenheit warmer than others.

Clothing Color

This one might seem absurd, but mosquitoes use vision (along with scent) to locate humans, so wearing colors that stand out (black, dark blue or red) may make you easier to find, at least according to Jonathan Day, a medical entomologist at the University of Florida, in commentary he gave to NBC.

Genetics

As a whole, underlying genetic factors are estimated to account for 85% of the variability between people in their attractiveness to mosquitoes regardless of whether it’s expressed through blood type, metabolism, or other factors. Unfortunately, we don’t (yet) have a way of modifying these genes.

Natural Repellants

Some researchers have started looking at the reasons why a minority of people seem to rarely attract mosquitoes in the hopes of creating the next generation of insect repellants. Using chromatography to isolate the particular chemicals these people emit, scientists at the UK’s Rothamsted Research lab have found that these natural repellers tend to excrete a handful of substances that mosquitoes don’t seem to find appealing. Eventually, incorporating these molecules into advanced bug spray could make it possible for even a Type O, exercising, pregnant woman in a black shirt to ward off mosquitoes for good.

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The writer is a Professor and Head Department of Entomology, National Institute of Preventive and Social Medicine (NIPSOM).