The most common blood type in the world is O positive. Globally, about 47% of people have type O blood, and the vast majority of them are Rh-positive, making O positive the single most prevalent blood type on the planet. Type A comes in second at roughly 41%, followed by type B at 9% and AB at just 3%.
What Makes Blood Types Different
Your blood type comes down to tiny protein molecules, called antigens, sitting on the surface of your red blood cells. If you have A antigens, you’re type A. B antigens make you type B. Both A and B antigens together make you type AB. And if you have neither, you’re type O.
There’s a second layer to the system: the Rh factor. This is another protein that’s either present on your red blood cells or not. If it’s there, you’re “positive.” If it’s missing, you’re “negative.” Combine the two systems and you get eight common blood types: A+, A-, B+, B-, AB+, AB-, O+, and O-.
Your plasma, the liquid part of your blood, carries the flip side of whatever antigens you have. Type A blood contains antibodies against B. Type B blood contains antibodies against A. Type O blood, having no antigens at all, carries antibodies against both A and B. This is why mixing the wrong blood types triggers a dangerous immune reaction: your plasma attacks the foreign antigens on the transfused cells.
Why O Positive Is So Common
The dominance of type O blood likely traces back to evolutionary advantage. Because type O red blood cells carry no A or B antigens, they don’t provide easy docking points for certain parasites and pathogens. Over thousands of generations, this may have given type O individuals a slight survival edge in regions with high infectious disease burden, particularly malaria-prone areas of Africa and Central and South America, where type O prevalence is especially high.
The distribution isn’t uniform everywhere. In white populations, type A actually edges ahead at around 45%, with type O at about 40%. Type B sits at roughly 11% and AB at 4%. In parts of East Asia, type B is more common than it is in Europe or the Americas. These regional differences reflect centuries of population genetics, migration patterns, and local disease pressures.
O Positive vs. O Negative
O positive and O negative often get lumped together, but the distinction matters enormously in medical settings. O negative is the universal red cell donor type. Because O negative blood has no A antigens, no B antigens, and no Rh factor, it can be safely given to virtually anyone without triggering an immune reaction. In emergencies where a patient’s blood type is unknown, O negative is what gets pulled from the fridge.
O positive blood can be given to any Rh-positive recipient regardless of their ABO type, but it can cause problems for Rh-negative patients. That one protein makes all the difference. Only about 8% of people are O negative, yet O negative accounts for around 13% of hospital requests, creating a persistent gap between supply and demand at blood banks.
On the plasma side, the rules reverse entirely. Type AB plasma is the universal donor for plasma transfusions because it contains no antibodies against A or B antigens. Type O plasma, packed with both anti-A and anti-B antibodies, is the most restrictive.
Health Differences by Blood Type
People with type O blood have the lowest risk for heart attacks and blood clots in the legs and lungs compared to other blood types. The difference isn’t dramatic enough to change how you manage your cardiovascular health, but it’s a consistent finding across large studies. Researchers believe the connection involves clotting proteins that circulate at slightly lower levels in type O individuals.
Type O also showed a modest advantage during the COVID-19 pandemic. People with this blood type were somewhat less likely to test positive and tended to develop less severe illness than those with types A, B, or AB. Again, the effect was small, not the kind of thing that should change your behavior, but it adds to a growing picture of blood type influencing disease susceptibility in subtle ways.
The Rarest Blood Types
At the opposite end of the spectrum from O positive sits Rh-null blood, sometimes called “golden blood.” People with this type lack all Rh antigens, not just the main RhD protein but every one of the roughly 60 proteins in the Rh group. Only about 43 people have ever been reported to have it, the result of an extremely rare genetic mutation. Golden blood can be donated to anyone with rare Rh blood types, making it medically precious, but finding a compatible donor for someone with Rh-null blood is nearly impossible.
Among the standard eight blood types, AB negative is the least common, found in less than 1% of most populations. AB positive is also rare, typically under 4%. If you have one of these types, your donations are especially valuable for plasma supply, since AB plasma works as a universal donor.