The common experience of some individuals being consistently targeted by mosquitoes while others remain untouched has long fueled public curiosity. This selective feeding behavior suggests that mosquitoes are not choosing hosts at random. Scientific investigation has revealed that a complex array of human signals, working in concert, determines a person’s overall attractiveness to these blood-feeding pests.
The Truth About Blood Type O
Scientific studies show a statistical preference for Type O blood. Research has demonstrated that mosquitoes land on individuals with Type O blood significantly more often than on those with Type A blood. For instance, in one study, the insects landed on Type O subjects 83.3% of the time, compared to 46.5% for Type A subjects.
The preference is based on what is secreted through the skin’s surface, not the blood itself. Approximately 80% of the population are “secretors,” meaning they excrete chemicals containing their blood type antigens into body fluids like sweat. Type O individuals lack A and B antigens, meaning they secrete a precursor molecule, the H antigen, which mosquitoes appear to find more detectable or appealing.
While Type O blood is statistically more attractive, this genetic factor is only one of many signals a mosquito uses to choose a host. The secretor status allows the mosquito to essentially “read” the blood type externally before biting. Type B individuals generally fall between Type O and Type A in terms of landing preference, highlighting the graded nature of this attraction.
Initial Homing Mechanisms
A mosquito relies primarily on a highly sensitive chemical sensor to find a meal from a distance. The most important long-range attractant is carbon dioxide (CO2). Mosquitoes can detect the CO2 plume from a host from distances ranging from 30 feet to as far as 50 meters (about 164 feet).
The insect flies up the concentration gradient of this CO2 plume in a characteristic zigzag pattern until it gets closer to the source. Individuals who produce a greater volume of CO2, such as those who are exercising, are larger, or are pregnant, create a stronger and broader plume, effectively acting as a more obvious beacon.
Once the mosquito has flown within a range of about 5 to 15 meters, it begins to incorporate visual cues into its search strategy. Mosquitoes are generally attracted to movement and dark colors, which contrast against the horizon and signal a potential host nearby. This combination of a gaseous beacon and a visual target guides the insect into the immediate vicinity of a person.
Localized Chemical Signatures
After closing the distance, the decision to land and bite is based on the blend of chemicals emanating from the host’s skin. This individualized chemical cocktail is the largest determinant of who a mosquito chooses to target. One significant component of this close-range attraction is L-lactic acid, a compound produced in human sweat during metabolism and physical activity.
Lactic acid is a potent attractant for certain mosquito species, especially when combined synergistically with CO2 and other skin odors. In addition to chemical cues, the mosquito’s sensory organs detect body heat and moisture once it is within a meter of the target. Individuals with a higher core body temperature, such as those who have just finished a workout, offer a more compelling thermal signature.
The ultimate chemical signature is determined by the skin microbiota, the millions of bacteria that live on the skin’s surface. These bacteria break down compounds in sweat into a variety of volatile organic compounds (VOCs). The specific type and diversity of these bacteria create subtle variations in human odor that make some people more attractive than others. For example, high levels of specific carboxylic acids produced by the microbial community can make a person up to 100 times more appealing to certain mosquitoes.