Do Mosquitoes Prefer Certain Blood Types?

Using proboscis-amputated female Aedes albopictus in a forearm landing assay with 64 Japanese volunteers, the authors found Type O secretors attracted mosquitoes 83.3% of the time, versus 46.5% on Type A secretors. The H (O) antigen disaccharide on skin appeared more attractive than the A trisaccharide. Limitations are substantial: a single species not relevant to NH's Culex pipiens or Culiseta melanura, a small homogeneous sample, landing (not feeding) as the outcome, lab-reared insects, and no robust independent replication. A 2021 review by Fikrig & Harrington in Trends in Parasitology cautioned that many ABO mosquito studies have methodological flaws, and at least one study of Aedes aegypti suggests a preference for Type B odor — directly contradicting the Type O narrative.

Mosquitoes detect CO2 via maxillary palp receptors encoded by the Gr1/Gr2/Gr3 receptor complex from 5 to 15 meters away (McMeniman et al., Cell 2014). CO2 'gates' their searching behavior — it activates resting mosquitoes and switches on visual and thermal tracking. Larger body mass, higher metabolic rate, and physical activity all increase CO2 output. This is why adults typically get bitten more than young children, and why a sleeping person exhaling continuously at approximately 40,000 ppm is a far better target than a still child. Blood type has nothing to do with CO2 production. If you exhale more — because you're larger, more active, or pregnant — you attract more mosquitoes, regardless of what ABO antigen is on your skin.

Pregnant women attracted approximately twice as many Anopheles gambiae mosquitoes. Two mechanisms were confirmed: pregnant women exhale roughly 21% greater breath volume (substantially more CO2), and they have elevated abdominal skin temperature that releases more volatile skin compounds. This finding has been replicated in Sudan and Brazil. For New Hampshire pregnant women, this is clinically meaningful — EEE has a 30–35% case-fatality rate and NH had its first EEE fatality in a decade in 2024. Pregnant women in Rockingham County during July through October should treat repellent use as non-optional, not optional.

Identical twins showed strongly correlated attractiveness; fraternal twins did not. Narrow-sense heritability was approximately 0.62 for relative attraction and 0.67 for flight activity — comparable to heritability of height and IQ. This means roughly 62% of the variation in 'who mosquitoes bite' is explained by inherited traits. Those traits are likely mediated by inherited body-odor profiles and skin microbiome composition. De Obaldia et al. (Cell 2022) identified carboxylic acids produced by skin bacteria as the key driver of individual 'mosquito magnet' status. Blood type is an incidental correlate of this deeper biological reality, not a root cause.

A scoping review by Shelomi (Bulletin of Entomological Research 2022) examined every controlled study and found zero efficacy across all designs. The theory — that thiamine makes your skin smell unattractive to mosquitoes — has never been validated in a human field trial. Ingested garlic has similarly zero controlled evidence despite decades of anecdotal circulation. The mechanism proposed (garlic compounds exuding through sweat) has been tested and not demonstrated to reduce biting. Ultrasonic repellent devices deserve special mention because they are widely sold at retail. A Cochrane systematic review of 10 field studies found no measurable effect on mosquito biting rates, and the FTC has issued cease-and-desist orders against manufacturers for false-efficacy claims. None of these three interventions have any role in a NH mosquito protection strategy.