The question of what makes one person a mosquito magnet while another is ignored has long been a subject of scientific inquiry. Female mosquitoes require a blood meal to gain the necessary proteins for egg production. Their method for selecting a human host is not random, relying on a sophisticated series of chemical, thermal, and visual signals. This selection process moves through distinct phases, starting with long-range signals and narrowing down to specific compounds on the skin, including markers that reveal a person’s blood type.
The Primary Attractants
The initial signal a mosquito uses to locate a potential host from a distance is carbon dioxide (\(\text{CO}_2\)). This gas is expelled from human breath and acts as a beacon, detectable by the mosquito’s specialized maxillary palps and antennae from as far as 100 feet away. Mosquitoes track the plume of \(\text{CO}_2\), flying upwind and following the concentration gradient until they are closer to the source.
Individuals who exhale greater volumes of \(\text{CO}_2\) are automatically more attractive targets. This explains why larger adults or pregnant women, who breathe more heavily, often draw more attention. Once the insect is within approximately 50 feet, it integrates other physical cues. Visual signals, such as movement and the contrast of dark clothing, help guide the final approach to the host.
At the closest range, the mosquito switches to thermal tracking, using infrared sensors to detect the host’s body heat. This warmth guides the mosquito to areas of the skin with a high density of blood vessels. The combination of \(\text{CO}_2\), visual cues, and thermal signatures narrows the search field to a specific landing spot.
Blood Type and Secretor Status
While \(\text{CO}_2\) brings the mosquito close, specific chemical markers on the skin influence the final decision to bite. Studies consistently show a correlation between ABO blood type and mosquito preference, with Type O blood showing the greatest attraction. Research on the yellow fever mosquito, Aedes aegypti, indicates that Type O individuals are landed on nearly twice as often as those with Type A blood, with Type B falling in the middle.
The underlying mechanism for blood type detection is the host’s “secretor” status. Approximately 80 to 85 percent of the population are secretors, meaning they excrete water-soluble antigens corresponding to their blood type through their skin and other bodily fluids. For example, a Type A secretor will have Type A antigens on their skin, while a Type O secretor excretes the H antigen, the precursor for the A and B antigens.
Mosquitoes possess chemoreceptors on their legs and antennae that detect these secreted antigens on the skin surface. Being a secretor is a greater factor in attraction than the specific blood type itself, as non-secretors are less detectable to the mosquito’s sensory organs. These blood-type markers provide a chemical signature the mosquito uses to select its meal.
Metabolic and Genetic Markers
Beyond the ABO antigens, other chemical compounds produced by the body contribute to individual attractiveness, often influenced by genetics and metabolism. Lactic acid is a strong short-range attractant produced by the muscles and released through sweat, especially during physical activity. The combination of lactic acid with \(\text{CO}_2\) from heavy breathing creates an appealing cocktail of scents for the mosquito.
Other metabolic byproducts in sweat, such as ammonia and uric acid, also act as secondary attractants. These compounds are present in varying concentrations based on a person’s diet, genetics, and recent activity. The unique blend of these chemicals forms an individual’s specific body odor profile, which mosquitoes scrutinize.
The largest variable in this chemical profile is the skin microbiome, the community of bacteria that resides on the skin’s surface. These microbes break down compounds in sweat, such as amino acids and fatty acids, into volatile organic compounds (VOCs). The specific species and volume of these bacteria dictate the exact VOCs produced, explaining why some people’s body odor is more appealing than others.