Mosquitoes are not random in their selection of a host; their preference is rooted in subtle differences in human body chemistry. The tiny insects rely on a sophisticated, multi-stage detection system to locate a blood meal, integrating cues that range from long-distance gas detection to close-range chemical signaling. This complex process explains why some people consistently feel they are “mosquito magnets” while others are largely ignored. Blood type is only one of many factors that determine an individual’s total attractiveness to mosquitoes.
The Scientific Consensus on Blood Type Preference
Female mosquitoes display a measurable preference for certain blood types over others. Multiple studies have consistently shown that people with Type O blood are the most attractive targets for mosquitoes. This preference is so distinct that mosquitoes have been observed to land on Type O individuals nearly twice as often as they land on those with Type A blood, which is generally considered the least preferred type.
Mosquitoes are sensing chemical signals secreted through the skin. Approximately 80 to 85% of people are classified as “secretors,” meaning they release antigens corresponding to their blood type into their sweat and onto their skin surface. Mosquitoes can detect these secreted antigens, which are a form of oligosaccharide, before they attempt to pierce the skin.
Type O individuals secrete the H antigen, a molecular precursor to the A and B antigens, and this specific chemical signature appears highly appealing to the insects. The preference hierarchy generally places Type O as most attractive, followed by Type B, with Type A being the least attractive.
The Mosquito Detection System
The search for a host begins with long-range detection of the plume of carbon dioxide (\(\text{CO}_2\)) exhaled with every breath. Mosquitoes possess highly sensitive receptors on their maxillary palps that can detect \(\text{CO}_2\) from up to 50 meters away, triggering an upwind flight response.
As the mosquito approaches, the detection strategy shifts from olfaction to visual and thermal cues. Within a range of about five to fifteen meters, the insect begins to integrate visual signals, with high-contrast, dark objects being more easily detected. This visual targeting is often confirmed by the presence of \(\text{CO}_2\), meaning the insect only pays attention to visual targets once the chemical signal of a host is confirmed.
At a very close range, within about 70 centimeters, the mosquito uses thermal sensing to finalize its landing. They detect infrared radiation (IR) emitted by the host’s skin. This infrared detection helps them home in on the precise location of the skin for the blood meal.
Chemical Cues That Increase Attractiveness
Beyond blood type, a person’s unique body odor is composed of volatile organic compounds (VOCs) that are irresistible to mosquitoes at short range. The primary source of these attractive VOCs is the skin microbiome, the unique community of bacteria living on the skin’s surface. These bacteria metabolize compounds in sweat, such as amino acids and lipids, producing a specific chemical bouquet that mosquitoes can sense.
Lactic acid is one of the most prominent attractant compounds, which is why physical activity that increases lactic acid production on the skin makes an individual significantly more attractive. Other attractive byproducts include ammonia, uric acid, and various short-chain carboxylic acids. The specific composition and diversity of a person’s skin microbiome is largely determined by genetics, explaining why some people are consistently more attractive.
The combination of \(\text{CO}_2\) and these skin volatiles, particularly lactic acid, acts synergistically, creating a much stronger attraction than either factor alone.
Strategies for Reducing Mosquito Bites
Since blood type and the composition of the skin microbiome cannot be easily changed, prevention focuses on disrupting the mosquito’s detection system. The most effective strategy involves using an Environmental Protection Agency (EPA)-registered insect repellent containing active ingredients like DEET, Picaridin, or Oil of Lemon Eucalyptus (OLE). Repellents with DEET concentrations between 10% and 30% offer reliable protection for several hours.
Wearing clothing that minimizes visual and thermal cues is another simple strategy. Mosquitoes are attracted to dark colors, such as black, red, and navy, which absorb heat and stand out visually against the horizon. Opting for light-colored, loose-fitting clothing can make a person less conspicuous.
Minimizing outdoor activity during peak mosquito hours, typically dawn and dusk, can reduce exposure to the insects when they are most actively feeding. Eliminating sources of standing water around the home, such as in flowerpots, gutters, or old tires, removes the breeding grounds for mosquitoes and helps control their population.