They’re A, B, AB, and O. A tiny bit of protein, called an antigen, on the surface of a red blood cell determines what type you have. If you have the A antigen, you have blood type A; the B antigen gives you blood type B. If you have both A and B, you have blood type AB. If you have no antigens, you have blood type O. If you have this on your red blood cells, you have a positive blood type. If you don’t, you have a negative blood type. For example, if you have the A antigen and the Rh factor, your blood type is A positive. If you have the B antigen but no Rh factor, your blood type is B negative. A simple blood test can tell you which type you have. Type O is the most common type: 43% of Americans have it. On the flip side, if you have AB blood, you’re at higher risk compared to people with other blood types. That’s also the rarest type — less than 10% of people in the U.S. have it. They’re 82% more likely to have the issues that can lead to dementia than people with other types. People with type O have the lowest risk of developing the condition. Ideally, you should get your own blood type if you need a transfusion (when blood from one person is given to another). But in an emergency, O negative can be used by anyone with any blood type. That’s because it doesn’t have any of the antigens — A, B, or Rh — that can lead your immune system to attack it. About 7% of people in the U.S. have O negative blood. They’re known as “universal recipients” because their blood has all the antigens — A, B, and Rh. If you have this type, your body will recognize any other blood type as its own. You may have heard of this idea, but there’s no evidence to support it. No studies have shown any health effects of specific foods on any blood type. A woman’s blood can attack her baby’s blood cells if she’s Rh negative and the baby is Rh positive. This is called rhesus disease, and medication can prevent it. If you’re pregnant, you should have a blood test to find out your Rh factor. If you’re Rh negative, your doctor will recommend that you take the medication to be safe. Source
