What blood type do mosquitoes bite most?
If you ask a mosquito, the answer is basically: “whichever of you smells and breathes the most like a meal.” Blood type barely enters into it. The popular belief is that Type O is the mosquito magnet, and there is a sliver of research behind that idea — but it is a much smaller and shakier sliver than the internet suggests.
The most-cited evidence is a 2004 laboratory study by Shirai and colleagues in Japan. Using the Asian tiger mosquito (Aedes albopictus), researchers reported that mosquitoes landed on Type O volunteers about 83% of the time, compared with roughly 46% for Type A, with Type B and AB in between. That is a real, published result. But it involved fewer than 100 people, tested one mosquito species under short controlled conditions, and has not been convincingly reproduced at scale. No large review of mosquito attraction ranks blood type among the strong, reliable drivers.
So the accurate, non-clickbait answer: mosquitoes may land on Type O a little more, but if you are the one being devoured at a GTA backyard barbecue, your blood type is almost never the reason. Read on for what is.
Do mosquitoes like certain blood types at all?
Possibly, but weakly. A couple of studies going back to the 1970s (including work by Wood and colleagues) and the 2004 Shirai study found some ABO patterns. Others found nothing meaningful. When an effect showed up, the pattern usually looked like the table below — but note how small and inconsistent the differences are.
| Blood type | Reported attraction (where any effect was found) | Strength of evidence |
|---|---|---|
| Type O | Landed on most often (~83% in Shirai 2004) | Weak — small samples, rarely reproduced |
| Type B | Intermediate | Very weak |
| Type AB | Intermediate | Very weak |
| Type A | Landed on least often (~46% in Shirai 2004) | Weak — not consistently confirmed |
The key phrase is “where any effect was found.” Plenty of studies find no blood-type effect at all. Treat this table as a curiosity, not a rulebook — there is no blood type that makes you invisible to mosquitoes, and none that guarantees you get eaten.
Why would Type O blood attract mosquitoes more?
Here is the twist most articles skip: mosquitoes cannot read your blood type. They have no way to sense the ABO antigens sitting on your red blood cells until after they have already bitten you. So if there is any real Type O effect, it must come from something a mosquito can actually detect from the outside — your skin.
That points to secretor status. About 80% of people are “secretors,” meaning they release chemical markers of their blood-group antigens through saliva, sweat, and the surface of their skin. Mosquitoes may pick up on these secreted compounds. Because being a secretor and being Type O often get studied together without separating them, it is genuinely hard to tell whether any signal comes from the O antigen itself or simply from being a secretor. In other words, the “Type O” story may really be a “secretor” story wearing a costume.
One study found that secretors were bitten more than non-secretors regardless of blood type — which suggests the chemical layer on your skin matters more than the letter of your blood group. It is the scent, not the blood.
What blood type do mosquitoes hate or bite the least?
In the studies that found any pattern, Type A tended to be landed on least. But do not go feeling smug (or doomed) about your blood group. The differences were small, the studies were few, and no ABO type actually repels mosquitoes. There is no such thing as mosquito-proof blood.
If you are the person at the campfire who never gets bitten while everyone else swats, the likely reasons have nothing to do with blood type: you may exhale less CO2, run a cooler skin temperature, or simply host a different mix of skin bacteria that mosquitoes find less appealing. Those are the levers that matter.
Myth vs fact: blood type and mosquito bites
| The myth | The reality |
|---|---|
| “Mosquitoes love Type O blood.” | One small 2004 study hints at it. It is a weak, unconfirmed trend — not an established fact. |
| “Type A blood repels mosquitoes.” | No blood type repels mosquitoes. Type A was simply landed on slightly less in a couple of studies. |
| “Mosquitoes can sense my blood type.” | They cannot detect ABO antigens before biting. They read your breath, heat, and skin chemistry. |
| “Blood type is why I get bitten so much.” | Almost certainly not. CO2 output, body heat, and skin bacteria explain the vast majority of it. |
| “Nothing I do will change how much I get bitten.” | False. Repellents, clothing, timing, and yard treatment all cut bites dramatically. |
What actually attracts mosquitoes to you (far more than blood type)
Mosquito attraction is a layered process, and blood type is nowhere near the top of the list. Here is roughly how much the real factors matter, from strongest to weakest.
| Factor | How mosquitoes use it | Impact |
|---|---|---|
| Carbon dioxide (CO2) | Detected from your breath up to ~50 m away — the main long-range signal | Very high |
| Skin bacteria & body odour | Microbes produce lactic acid, ammonia & carboxylic acids mosquitoes track close-up | Very high |
| Body heat & moisture | Used at short range to home in on exposed, warm, sweaty skin | High |
| Body size & metabolism | Bigger, more active bodies exhale more CO2 and give off more heat | Moderate |
| Pregnancy | Higher CO2 output and slightly warmer skin | Moderate |
| Exercise & alcohol | Raise CO2, heat, sweat and lactic acid; even one beer measurably increases bites | Moderate |
| Dark clothing | Easier for mosquitoes to see visually against a background | Low–moderate |
| Blood type | Possible weak effect via secreted skin compounds — unproven | Low |
Notice where blood type sits: dead last. For a deeper breakdown of the scent and CO2 story, see our full guide to what attracts mosquitoes to you, and if you suspect you are one of the unlucky 20%, our Am I a mosquito magnet? quiz walks through the real risk factors.
What blood type “repels” mosquitoes? (Spoiler: none)
Let’s be blunt: no blood type repels mosquitoes. You cannot change your ABO type — it is set at birth for life — and even if you could, the payoff would be tiny. Anyone selling a “blood-type mosquito hack” is selling a myth.
What genuinely reduces bites for every blood type is straightforward:
- Use a Health Canada-registered repellent with DEET or icaridin on exposed skin. See our Ontario mosquito repellent guide for what works and for how long.
- Cover up with light-coloured, loose, long sleeves and pants at dawn and dusk when mosquitoes peak.
- Cut the scents that draw them in and lean on the ones they avoid — our roundup of smells mosquitoes hate covers the evidence.
- Kill breeding sites — dump standing water in gutters, planters, and toys every few days so eggs never hatch.
- Treat your yard. A professional barrier spray (from $99 per treatment across the GTA) coats the shaded leaf undersides and shrubs where mosquitoes rest, dropping the population you are exposed to in the first place.
Why this matters in Ontario
Beyond the itch, mosquito bites carry a real if modest health risk in the GTA. Public Health Ontario and the Public Health Agency of Canada (PHAC) track West Nile virus in local mosquito populations every summer, and cases turn up across the province most years, typically peaking in late summer. The virus does not care about your blood type — the way you lower your risk is by lowering your number of bites, full stop.
This is general information, not medical advice. If you develop a fever, severe headache, a spreading rash, or other worrying symptoms after mosquito bites, contact your healthcare provider, and in an emergency call 911.
The bottom line
Could your Type O blood make you a slightly bigger target? Maybe, at the margins — but the science is weak and the effect, if it exists, is dwarfed by things you can actually influence. You cannot change your blood type. You can change how much CO2, heat, and skin-bacteria scent you broadcast, whether you wear repellent, and whether the yard around you is crawling with mosquitoes in the first place. Focus your energy there, and blood type becomes a footnote.