A person's blood type is determined by "the presence or absence of certain antigens – substances that can trigger an immune response if they are foreign to the body"
Four major blood groups exist and are categorized by the presence or absence of two antigens, A and B, on the surface of red blood cells.
Additionally, there is a protein called "the Rh factor," which can also be present (+) or absent (–).
A (+) A (-) B (+) B (-) O (+) O (-) AB (+) AB (-)
These factors help define the eight most common blood types:
But of these eight, which is the most common?
According to the American Red Cross, the most common blood type is O positive, which is the blood type for 37% of the population.
The second most common blood type is A positive.
There are over 600 other known antigens, and the absence or presence of them creates "rare blood types," says the American Red Cross.
However, statistically, AB negative is rarer than other blood types. The blood type of B negative is also uncommon.
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