The question of whether mosquitoes prefer certain people has long been a subject of popular curiosity, often leading to speculation about factors like “sweet blood.” Scientific inquiry has moved past folklore to identify a complex interplay of genetic, metabolic, and chemical signals that dictate a person’s attractiveness to these blood-feeding insects. Female mosquitoes require a blood meal for egg production and rely on a highly tuned sensory system to locate their hosts. Researchers have isolated the specific biological cues that make some individuals more appealing targets than others.
The Direct Answer: Blood Type Preference
Research has consistently shown that mosquitoes exhibit a measurable preference for certain blood types. Studies indicate that individuals with Type O blood are statistically more attractive to mosquitoes than those with other blood types, especially Type A. In trials, Type O individuals experienced nearly twice the number of mosquito landings compared to those with Type A blood.
This preference is not based on the blood itself but on specific chemical markers secreted onto the skin. Roughly 80% of people are “secretors,” meaning they release water-soluble antigens corresponding to their blood type onto their skin surface. The Type O blood type corresponds to the H antigen, which is a precursor sugar molecule to the A and B antigens.
The detection of these secreted blood-type antigens guides the mosquito’s landing choice. Studies found that Type O secretors were significantly more attractive to mosquitoes than Type A secretors. This suggests the presence of the Type O-related antigen on the skin acts as an olfactory cue, drawing the mosquito in for a bite.
Chemical Signals That Attract Mosquitoes
Mosquitoes rely on sensory cues to locate a potential host. The longest-range signal is the plume of Carbon Dioxide (\(\text{CO}_2\)) exhaled during respiration. Mosquitoes can detect \(\text{CO}_2\) from distances as far as 164 feet, using it as a general beacon to identify warm-blooded animals. Larger people, pregnant women, or those who have recently exercised tend to exhale more \(\text{CO}_2\), making them more visible to the insects.
Once a mosquito is within a few feet of a target, it tracks volatile organic compounds (VOCs) and heat. Body heat acts as a short-range cue, which mosquitoes detect using specialized heat-sensing organs called thermoreceptors. The warmth emitted by the skin confirms the presence of a viable blood source.
The body’s chemical emissions, particularly those in sweat, provide highly specific attractants. Lactic acid is a well-known compound in sweat that strongly attracts mosquitoes, especially when combined with \(\text{CO}_2\). Other volatile compounds found in human sweat, such as acetone, uric acid, and ammonia, also serve as potent attractants, guiding the mosquito to the skin.
The Role of Skin Microbiome and Genetics
Variation in mosquito attraction among people is explained by the unique biological profiles of individuals. The skin microbiome, the community of bacteria living on the skin, plays a major part in producing the attractive VOCs. These bacteria break down compounds in sweat, such as amino acids and sugars, converting them into the scents mosquitoes find irresistible.
People whose skin harbors a higher abundance but lower diversity of certain bacteria strains often produce a more attractive odor bouquet. Bacteria such as Staphylococcus and Corynebacterium species produce various carboxylic acids that are highly attractive to mosquitoes. Lactic acid, a known attractant, is a byproduct of this bacterial metabolism on the skin.
Genetic factors contribute to a person’s metabolic rate, influencing the natural production of specific chemicals in sweat and breath. The production levels of compounds like uric acid or the ratios of specific carboxylic acids are genetically determined. This inherited chemistry, combined with the composition of the skin’s microbial community, creates a unique scent profile that explains why some individuals are consistently attractive to mosquitoes.
Actions to Reduce Mosquito Bites
For those attractive to mosquitoes, several proactive measures can significantly reduce the risk of bites. The most effective defense is the application of a repellent containing the active ingredients DEET or Picaridin, which are recommended by health organizations. DEET concentrations between 7% and 30% offer reliable protection, with higher concentrations extending the duration of efficacy.
Picaridin, a synthetic compound that mimics a substance found in black pepper, is effective and often preferred for its lack of odor and non-greasy feel. A 20% Picaridin formulation offers comparable protection time to many DEET products. Applying repellents to exposed skin and clothing helps mask human scents.
Wearing long sleeves and pants, especially in light colors, provides a physical barrier and makes you less visually conspicuous to the insects, which are drawn to dark shades. Reducing standing water sources around the home, such as in flowerpots or clogged gutters, eliminates breeding grounds and helps manage the local mosquito population.