When you find yourself covered in mosquito bites while others remain untouched, the common assumption is that these insects must prefer your blood. While blood type is a genuine factor in mosquito attraction, it is only one component in a complex system of sensory cues used by the female mosquito to locate a meal. The quest for blood, necessary for egg development, is guided by biological signals, with your unique scent profile and breath often overshadowing the influence of your ABO blood group. Understanding this hierarchy of attraction reveals why some individuals are consistently targeted.
The Research on Blood Type Preference
Scientific investigations show that mosquitoes prefer human hosts with Type O blood. Laboratory studies indicate that mosquitoes land on and feed from Type O individuals nearly twice as often as they do from those with Type A blood, with Type B falling in between. This preference is not due to the blood itself, but rather to the chemical signals a person emits through their skin.
The mechanism behind this preference is tied to “secretor status.” Approximately 85% of people are secretors, meaning they release specific blood type antigens—molecules that determine your blood group—onto their skin’s surface and into other bodily fluids. A Type O secretor releases the H antigen, a precursor molecule for the A and B antigens, which is believed to be the primary attractant.
Mosquitoes are thus not tasting the blood, but rather detecting the chemical signature of the blood type before they even land. Research shows that Type O secretors are significantly more attractive than Type A secretors, emphasizing that the exposed antigen on the skin is the true lure, not the internal blood composition. Secretor status is often a more important determinant of attraction than the blood type itself.
Chemical Signatures on the Skin
Beyond blood group antigens, volatile organic compounds (VOCs) on the skin act as a powerful, close-range beacon for mosquitoes. These chemical signatures are created when the skin’s resident microbiome—the billions of bacteria living on the surface—breaks down non-odorous compounds found in human sweat and sebum. The resulting metabolic byproducts are released as distinct odors into the air, which the mosquito’s olfactory system detects.
The composition of a person’s skin microbiome, which is largely unique to the individual, determines the specific mix of attractive and repulsive odors produced. Highly attractive individuals often produce significantly higher levels of certain compounds, such as carboxylic acids. The skin bacteria Staphylococcus epidermidis and Corynebacterium amycolatum are known to produce L-(+)-lactic acid, a specific byproduct of sweat metabolism that is a potent attractant for many mosquito species.
The concentration and blend of these chemicals create the “mosquito magnet” effect, explaining why two people with the same blood type can have drastically different bite rates. The combination of lactic acid, ammonia, and various carboxylic acids forms a complex odor plume that is appealing to the insect. Some studies suggest that certain skin volatiles, like octanol, only become attractive when combined with the presence of lactic acid, highlighting the importance of the chemical blend rather than any single compound.
Long-Range Detection: Carbon Dioxide and Heat
While skin chemistry is the specific calling card, finding a host begins with two long-range signals: carbon dioxide and heat. Carbon dioxide (CO2), which humans exhale with every breath, serves as the primary long-distance orientation cue for female mosquitoes. Specialized receptors on the mosquito’s maxillary palps can detect the plume of CO2 from distances up to 50 meters away, acting as a broad signal that a warm-blooded host is nearby.
Once a mosquito detects this CO2 plume, it flies upwind and tracks the concentration gradient to home in on the source. This initial detection of CO2 “gates” or activates the mosquito’s response to other sensory inputs, like heat and certain odors. Without the CO2 trigger, the mosquito may not even respond to the presence of other attractive cues.
As the mosquito gets closer to the CO2 source, it begins to sense the host’s body heat and moisture. Body heat is radiated as infrared energy, allowing the mosquito to pinpoint a precise landing spot. The combination of warm body temperature and the humidity in the air from exhaled breath and skin moisture creates convection currents that guide the insect to the final target area, transitioning the mosquito to close-range thermal targeting.
Behavioral and Physiological Influences
Several temporary or physiological states can significantly increase a person’s attractiveness by amplifying the release of key chemical and thermal signals. Physical exercise, for instance, dramatically increases both the metabolic rate and the production of carbon dioxide, creating a larger and more detectable plume. Exercise also leads to increased body temperature and greater production of lactic acid through sweat, intensifying the close-range chemical signal.
Pregnancy is another state that causes a notable increase in mosquito attraction, with pregnant women being nearly twice as attractive to some species. This heightened appeal is linked to an elevated body temperature, which is often around 0.7°C higher in the abdomen, and an increased volume of exhaled air. The 21% greater volume of breath means a more substantial CO2 plume for mosquitoes to follow.
The consumption of alcohol, specifically beer, has been shown to increase a person’s appeal to mosquitoes, although the exact mechanism is not fully understood. The color of clothing can also play a role, as mosquitoes use vision for target acquisition after detecting CO2. They are particularly drawn to dark colors, such as black, navy, and red, because these hues contrast sharply with the background and absorb heat more readily, making the host a more visible and warmer target.