Victor J. Blue/The New York Times

Mosquitoes might not prefer certain blood types, but they still tend to bite some people more than others.

September 13, 2021

Debugging the Myth: Do Mosquitoes Really Prefer to Bite Certain People?

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While Cornell students enjoy the last nights of summer relaxing under the glow of the setting sun on Libe Slope, some find themselves ravaged by mosquito bites while others find themselves walking away unscathed. 

Although mosquitoes do prefer to feast on some people more than others, this preference has more to do with the chemistry taking place on one’s skin rather than commonly misconceived reasons such as blood type.

So-called “mosquito season” begins when temperatures consistently surpass 50 degrees Fahrenheit, typically ranging from late spring to early fall in Ithaca.

The most mosquitoes die when low temperatures freeze standing water, the typical mosquito breeding ground. During the fall and winter, however, some female mosquitoes take cover in warm areas like animal burrows, attics or basements.

According to Prof. Laura Harrington, entomology, these female mosquitoes are the ones that bite humans as they require certain amino acids — the building blocks of proteins — and nutrients like iron from blood to produce their eggs.

Harrington said that mosquitoes rely on several sensory signals to locate humans, including carbon dioxide emission, heat and vision.

“We do know that some odors are used for longer range attraction to people, like carbon dioxide,” Harrington said. “Then, once the mosquito is closer they can use heat, vision and other sensory mechanisms to finally hone in on their victim.”

Those who are easier for mosquitoes to spot — particularly people who have just finished exercising — are prime targets for the insects. This, in part, is due to the production of lactic acid, a product that accumulates in muscle as a result of exercise and the scent of which is particularly attractive to mosquitoes. The additional increase in body temperature and carbon dioxide exhalation make convenient victims out of those who exercise.

Harrington said that a combination of over 300 compounds on human skin can create a concoction that attracts mosquitoes. Some research has even shown that the microorganisms living on people’s skin can impact their body odor, serving to attract mosquitoes to certain fragrant individuals.

“In recent years, skin bacteria have been identified that might play a role in producing odors that are attractive to mosquitoes and there is variation in this microbiota from one person to the next,” Harrington said.

Human body odor is produced when skin bacteria break down proteins in sweat. Some secretions are metabolized into fatty acids, and bacterial waste products from this process contribute to odor.

Although blood type is commonly expected to be a factor involved in mosquitos’ preferences — and some studies provide evidence mosquitoes prefer type O — Harrington holds that this claim is largely a myth.

Blood type is characterized by the presence of certain antigens, substances that trigger immune responses to foreign substances in the body, and proteins on red blood cells.

Blood type seems to have no relationship with body odor, let alone other sensory mechanisms on which mosquitoes rely. The presence or absence of antigens and surface proteins makes no changes to the amino acid and nutrient content of human blood, so mosquitoes have no need to desire one blood type over another. Accordingly, Harrington insists that blood type is not at all a factor in mosquito-host attraction, and thus that the idea of mosquitoes preferring a certain blood type is simply a myth.

Harrington acknowledged that sources hold differing opinions on whether there is currently credible research that definitively proves whether mosquitoes prefer a certain blood type. For now, all we can do is wait for the inevitable, harsh Ithaca winter to rid our lives of the bothersome bugs for a few short months.