Why certain people seem to be “mosquito magnets” while others go relatively untouched is a frequent question. The female mosquito, the only one that bites, seeks a blood meal to provide the necessary proteins for egg production. This search for a host is a multi-stage process involving an array of sensory inputs. Differences in human biology, ranging from exhaled air to the skin’s microscopic landscape, create a complex profile of host desirability.
The Role of Blood Type in Attraction
A person’s blood type plays a part in determining their attractiveness to a mosquito. Individuals with Type O blood are significantly more likely to be bitten than those with Type A blood, with Type B falling in between. This preference is linked to genetic markers present on the skin surface, not the blood itself. Approximately 80% of the population are “secretors,” meaning they secrete water-soluble antigens corresponding to their blood type onto the skin. Mosquitoes, particularly species like Aedes albopictus, can detect these specific antigens in the secretions. For instance, a person with Type O blood secretes the H antigen, which is highly attractive.
Chemical Signatures and Skin Microbiome
While blood type is a contributing factor, mosquito attraction is primarily driven by chemical signals operating over long and short distances. The initial long-range beacon is carbon dioxide (\(\text{CO}_2\)), which is exhaled with every breath and can be detected from over 10 meters away. The mosquito uses specialized receptors to follow the \(\text{CO}_2\) plume as it disperses, allowing it to orient toward a potential host.
As the mosquito closes the distance, it detects volatile organic compounds (VOCs) emanating from the skin. These odors are short-range attractants that help the insect pinpoint the exact landing site. Key metabolic byproducts in human sweat, such as lactic acid, ammonia, and octenol, are attractive to female mosquitoes. The amount of these chemicals produced varies based on an individual’s metabolic rate, increasing during exercise or pregnancy.
The specific composition of an individual’s skin microbiome profoundly influences the production of these attractive odors. Bacteria living on the skin metabolize non-volatile compounds in sweat, breaking them down into volatile chemicals. Individuals with a higher abundance but lower diversity of certain bacteria, such as Staphylococci and Corynebacterium, often produce more appealing VOCs. The resulting scent profile dictates whether a person is considered an attractive target.
Physical Signals Mosquitoes Use to Locate Hosts
Once a mosquito is within a few meters of a host, it uses physical cues to finalize its approach. One important close-range signal is thermoreception, the ability to sense heat. The human body emits heat in the form of thermal infrared radiation, which mosquitoes can detect from up to 0.8 meters away. This thermal signature acts as a navigational aid, guiding the mosquito as it flies through the \(\text{CO}_2\) and odor plumes.
At a distance of less than 10 centimeters, the mosquito can also sense the convection heat and humidity rising from the skin. The warmth confirms the presence of a living, blood-filled target, distinguishing a person from a non-living source of attractive chemicals.
Visual cues also play a role, particularly in the final stages of host-seeking behavior. Mosquitoes are drawn to the sight of large, dark objects against the horizon. Dark colors, such as black, red, and orange, absorb more heat and provide a better visual contrast, making the host easier to spot and track from a moderate distance.