Mosquitoes are universally disliked insects, and many people feel they are disproportionately targeted by these blood-feeding pests. This observation, that some individuals are “mosquito magnets” while others go unnoticed, is rooted in complex biology. Female mosquitoes require a blood meal to produce eggs, making them highly efficient hunters that use sensory tools to find a host. Scientific investigations have explored whether factors like blood type influence this selection process.
Blood Type and Secretor Status
Research suggests that an individual’s ABO blood type influences how attractive they are to mosquitoes. Studies have found that people with Type O blood are more likely to be bitten than those with Type A blood, with Type B falling in between. In controlled landing preference tests, the difference between Type O and Type A individuals has been found to be significant.
This preference is not about the blood itself, but the chemical signals released through the skin. A person’s “secretor status” determines whether they release water-soluble antigens corresponding to their blood type onto the skin surface. Approximately 80 to 85% of the population are secretors, meaning the chemical signature of their blood type is detectable by mosquitoes before a bite occurs.
Mosquitoes detect the H antigen, which is the precursor molecule for the A and B antigens and is the primary antigen found in Type O individuals. Mosquitoes show a significantly higher landing preference for Type O secretors compared to Type A secretors. The combination of being a secretor and having Type O blood creates a more attractive chemical profile.
Primary Signals Used for Host Location
While blood type contributes to host preference, it is a relatively short-range signal compared to the primary cues. The most important long-range attractant is carbon dioxide (CO2), which humans exhale in a plume. Mosquitoes can detect this CO2 plume from distances up to 160 feet, using specialized sensory organs on their maxillary palps to activate host-seeking flight.
Once closer, the mosquito transitions to using a combination of other cues to pinpoint its target. One potent short-range chemical signal is lactic acid, which is produced by the human body and concentrated in sweat, especially after physical activity. Lactic acid is considered a human-signifying host cue because its concentration is uniquely high in human skin emanations compared to other vertebrates.
Lactic acid alone is not a strong attractant, but it works synergistically with the CO2 plume to increase a mosquito’s attraction to a host. In the final stage of approach, the mosquito uses thermal and visual cues, such as body heat and moisture from sweat, to confirm the blood source location. These combined signals—chemical, thermal, and visual—create a highly effective targeting system.
Individual Genetic and Microbiome Differences
Even among individuals with the same blood type and secretor status, mosquito attraction varies significantly. This difference is largely explained by genetics and the skin microbiome. The human skin hosts a diverse community of bacteria that break down compounds in sweat and sebum.
This microbial activity produces most of the volatile organic compounds (VOCs) that mosquitoes find attractive. Without the skin microbiome, human sweat would be nearly odorless, demonstrating the bacteria’s critical role in generating the host-seeking chemical signature. The specific type and diversity of bacteria determine the exact mixture of VOCs released.
Individuals identified as “mosquito magnets” produce certain short-chain carboxylic acids at higher levels than less-attractive people. These fatty acids are metabolic byproducts of the skin bacteria breaking down lipids in the skin’s protective barrier. The unique microbial ecosystem on a person’s skin is a major, genetically influenced variable determining their level of attractiveness.