B positive is one of the eight main blood types, found in about 9% of the U.S. population. It means your red blood cells carry the B antigen on their surface and the Rh factor protein, which is what makes it “positive.” Your plasma naturally contains antibodies against the A antigen, so your immune system would react to blood that carries it.
What B Positive Actually Means
Your blood type is determined by two systems working together. The first is the ABO system, which classifies blood based on which sugar molecules (antigens) sit on the surface of your red blood cells. If you’re type B, your cells carry the B antigen. Your plasma, the liquid part of your blood, contains anti-A antibodies that would attack any blood cells carrying the A antigen.
The second system is the Rh factor. “Positive” means your red blood cells carry an additional protein called the Rh(D) antigen. About 85% of people are Rh positive. Combine these two systems and you get B positive: B antigen present, Rh protein present, anti-A antibodies in your plasma.
How Common Is B Positive?
According to the American Red Cross, roughly 9% of the U.S. population has B positive blood. That makes it less common than O positive (the most prevalent type) or A positive, but considerably more common than any of the negative blood types. In the UK, about 1 in 13 blood donors is B positive. Globally, B positive is more prevalent in parts of Central and South Asia, where it can account for 25% or more of the population.
Who You Can Donate To and Receive From
If you’re B positive, you can receive red blood cells from two blood types: B (positive or negative) and O (positive or negative). That gives you four compatible donor types. You can donate red blood cells to people with B positive or AB positive blood.
B positive blood plays a particularly important role for patients with sickle cell disease and thalassemia, conditions that often require repeated transfusions. NHS Blood and Transplant notes there is currently very high demand for B positive donations, especially for a specific subtype called Ro that is more common in people of Black heritage.
How You Inherited It
Blood type is genetic. You inherited one ABO gene from each parent. The B gene is dominant over O but co-dominant with A, meaning if you received a B from one parent and an O from the other, you’re type B. If you received a B from one parent and an A from the other, you’d be type AB instead. To be B positive, at least one parent must also carry the B gene, and at least one must carry an Rh-positive gene.
Two B positive parents can have a child who is type O if both carry a hidden O gene. They could also have a child who is Rh negative if both carry one copy of the Rh-negative gene. Blood type inheritance sometimes surprises families, but it follows straightforward genetic rules.
The Rh Factor and Pregnancy
Being Rh positive is the simpler scenario for pregnancy. Rh complications arise when an Rh-negative mother carries an Rh-positive baby. In that situation, the mother’s immune system can produce antibodies that attack the baby’s red blood cells, a condition that can cause severe anemia in the fetus. This risk is greatest during delivery and increases with each subsequent pregnancy if untreated.
If you’re B positive, your Rh status won’t trigger this reaction regardless of your baby’s blood type. The concern applies only to Rh-negative mothers. If your partner is Rh negative, however, your children could potentially be Rh positive, which would matter for your partner’s pregnancies.
Health Risks Linked to Blood Type B
Researchers have found statistical associations between blood type and certain diseases, though the increased risks are generally modest. People with non-O blood types, including B positive, tend to have slightly higher levels of clotting factors in their blood. This is linked to a somewhat greater risk of blood clots, ischemic heart disease, and early signs of atherosclerosis compared to people with type O.
For pancreatic cancer specifically, type B appears to carry the highest relative risk among all blood types, with one analysis finding an odds ratio of 1.72 compared to type O. Types A and AB showed smaller increases. Blood type B has also been associated with higher rates of certain infections, including those caused by E. coli, salmonella, and the bacteria responsible for tuberculosis and gonorrhea. These associations come from population-level studies. They describe trends across large groups, not individual destiny. Your overall lifestyle, family history, and environment matter far more than your blood type when it comes to disease risk.
The Blood Type Diet Has No Evidence
A popular book published in the 1990s proposed that people should eat differently based on their blood type, recommending that type B individuals focus on dairy products and certain meats. A study published in PLOS One tested this hypothesis directly by analyzing diet patterns and health markers across blood types. No significant health benefit was found for the type B diet. More importantly, when researchers matched people’s actual blood types to the supposedly ideal diets, the results didn’t change. The health effects of certain eating patterns were the same regardless of blood type. A systematic review reached the same conclusion: no evidence supports tailoring your diet to your blood type.