Last weekend I went to a backyard barbecue on a summer afternoon in south Florida. Sure enough, when the sun started to sink in the late afternoon those miniature, flying bloodsuckers started to appear. 

Nobody had any bug spray so some either left or went inside for the evening. For the ones who stayed outside, I noticed something. About half of the people started slapping their arms and were complaining about the mosquitoes. And the other half were oblivious and carrying on like they didn’t exist. 

That got me thinking, why do mosquitoes bite some people and not others? 

There are a lot of factors that go into why so here is my attempt to answer the question. But I’m not your doctor or anything so if you have a more serious mosquito problem don’t take this as the final word on the subject.

The two most obvious reasons mosquitoes bite some people and not others are body odor and blood type. That makes sense but it might be too obvious. Let’s dig a little deeper into the science of mosquitoes before we get there though.

Carbon Dioxide and Odors

Mosquitoes can detect carbon dioxide from up to 100 yards away which is how they find their prey. The good news for us is that the CO2 detection threshold for human beings isn’t nearly as high as other animals. The bad news is that by breathing we are emitting CO2 which makes us good prey.

It’s not just the CO2 though, mosquitoes also use other odors to detect their victims. They can detect lactic acid which you emit through your sweat and uric acid (one of the primary waste products in humans). Mosquitoes use a heat-sensing organ called a thermoreceptor to find you as well, so if it’s hot out this is going to help them find you even easier because they can follow your body heat.

Blood Type

What about blood type? Well, believe it or not, mosquitoes don’t actually have teeth so they use an elongated mouthpart called a proboscis. There are three basic types of bloodsuckers: Anopheles, Culex, and Aedes. Type O is the most common in the US with around 39% of people being type O while only 17% are type A. It’s not surprising that they would target this type more frequently because they are thirsty for fresh blood!

Body Odor

Now let’s get to body odor. Mosquitoes sense heat by way of a heat receptor called TRPA1 which leads them straight to you. They can also smell carbon dioxide, lactic acid, and uric acid which all come from your skin when you sweat. And if it’s hot outside that means mosquitoes will be able to find you faster since they can sense your body heat.

Consequently, you can see how body odor plays a role in why mosquitoes would be more attracted to one person over another. It’s not just sweating though. The bacteria that grow on your skin emit certain smells as well. Mosquitoes are even more attracted to people who have certain types of bacteria living on their skin. This brings us to our final answer: the science of your Skin Microbiome (the collection of all microorganisms on your skin).

Skin Microbiomes and Your Personal Mosquito Magnetism

Scientists from NC State University recently published research about how different people produce unique scents according to which type of bacteria is growing on their skin. This means that someone with a particular combination of microorganisms living on their skin (and producing certain scents) will be more likely to get bitten than someone with a different combination.

This study was conducted by coauthor and NC State professor Dr. Zoe Pratte who has been working in this field for about five years now. She found that “people consistently produce unique odors, even if they are related like twins” and that one person’s microbiome is totally unique from another person’s. What she did was take swab samples from axilla (armpit) areas of people and cultured the bacteria present on each person’s skin to see what grew back. Then she selected a few of those species and tested them against mosquitoes individually in a Y-tube olfactometer (a tube with a Y at the end for mosquitoes to go into).

So there you have it. It’s not how sweet your blood is and what color of your clothes are. It’s the combination of different bacteria living on your skin that makes you more or less attractive to mosquitoes. So what can we do about this? Well, you’re in the right place. We have several articles on just that.