You come from a hike in the mountains and notice that you are covered with itchy red bites from mosquitoes. But, on the other hand, your friends proclaim innocently that they don’t have any bites! Has this happened to you? It must have. And there’s a reason behind why some people are bitten more by mosquitoes than others. Mosquitoes can smell blood types and find certain people delicious based on their blood type, metabolism, clothes color, and even their exercise habits.

Mosquitoes find certain blood types delectable. People with type O blood are twice as likely to be bitten by mosquitoes than people with type A blood.

The blood type of a person is defined by the antigens that are present in the red blood cells. Antigens are certain substances that stimulate the immune system to produce antibodies. Now antibodies, in turn, fight antigens or foreign substances that can cause harm to the body. The antigens present in our blood can either be proteins or sugar complexes, and the mosquitoes are looking for proteins for their daily intake. Hence, our blood is their delicacy.

Now, just like different people love different cuisines, mosquitoes have their favorites of blood types too. In a study conducted in a controlled environment, scientists discovered a very peculiar trait in mosquitoes. They found out that mosquitoes love Type O blood twice as much as they love Type A blood. Type B is just average on the taste spectrum of the mosquitoes.

Now, how does a mosquito identify the blood type of a person? Well, 85% of people secret a chemical through their skin that provides information on their blood type. The mosquitoes look for this particular chemical signal and approach their targets. For the remaining 15% who do not secrete the chemical signal, mosquitoes are not much interested in them, regardless of their blood type.

Adults get bitten more than kids because mosquitoes locate their target by smelling the carbon dioxide exhaled through the breath. Adults exhale more CO₂ than kids and so get bitten more.

Another mechanism that mosquitoes use to locate targets is by smelling the amount of carbon dioxide that a person exhales. Mosquitoes have an organ known as the “maxillary palp.” This is the organ they use to detect the amount of CO₂ released by a person. They can detect CO₂ from as far as 164 feet. So people who exhale more CO₂, primarily large people, are bitten more by mosquitoes. This is the reason why children often get a bit less than adults.

Moreover, pregnant women release 21% more CO₂ than others and have a warmer body temperature. This makes them attract twice the number of mosquito bites.

In addition to carbon dioxide, mosquitoes are also attracted to people by the smell of their sweat. A person who has an active lifestyle is more likely to be bitten by mosquitoes. 

When people exercise, they sweat. The sweat is comprised of various chemicals such as lactic acid, ammonia, and uric acid. Also, as we have seen in the case of pregnant women, mosquitoes are attracted to people with higher body temperatures. Working out does that too for your body. This makes a person with an active lifestyle stand out in the crowd for mosquitoes.

Mosquitoes in a range can smell the chemicals secreted via sweat and can also detect warmer bodies. This is how they can easily locate their targets. Genetics also come into play as some people naturally expel uric acid and certain other chemicals. These chemicals are, in turn, easily detected by mosquitoes.

Mosquitoes don’t just rely on their sense of smell. They sometimes rely on their vision too. Wearing dark colors that stand out may make the person easier to find.

The smell is not the only medium through which mosquitoes identify their targets. This might come as a surprise, but mosquitoes use their vision as well to locate targets. People who wear dark colors such as black, red, dark blue, etc., stand out clearly for the mosquitoes. “Wearing black attracts mosquitoes” is a common phrase that most of us are familiar with. In reality, it’s not just black but any dark color. Mosquitoes find it easy to locate dark colors. This was also agreed upon by a medical entomologist, James Day, during his speech to NBC.

Another important factor that determines how much a mosquito is likely to bite a person lies in human genetics. It can be the person’s metabolism or the ability to release natural repellents that might make them unappealing to mosquitoes.

Genetics plays an important role when it comes to how likely it is for a mosquito to bite a person. 85% of the time. It is genetics that decides the attractiveness the mosquito will have to an individual person. Genetics includes the blood type, body odor, and metabolism of a person. These factors contribute to the decision made by mosquitoes whether they would bite the person or not. Some people are genetically engineered to release natural chemicals that automatically repel mosquitoes.

There is no way yet to decide which genes are responsible for such natural repellents, but scientists are conducting research on this. Identifying the genes would help scientists to decide on the next generation of natural mosquito repellents. Currently, scientists are using chromatography to pick out chemicals expelled by people who are natural repellers.

Scientists at the Rothamsted Research Laboratory, United Kingdom, have found a few chemicals that are just secreted by a few people. This group of people receives the least number of mosquito bites. They are the ones who are least attractive to mosquitoes. What the scientists are trying to do is use those specific chemicals to design a bug spray. The bug spray would be completely natural and even help those with blood Type O to protect themselves.

Another interesting fact is that mosquitoes are attracted to people drinking beer. Scientists suspect this might be due to the increase in ethanol levels in the body that is excreted via sweat, or it might be because alcohol increases a person’s body temperature, but neither of these factors was found to be the case when experiments were conducted. The affinity of mosquitoes to drinkers still remains a mystery for the science community.

[sources: 1, 2, 3, 4]