G6PD deficiency causes a disease in which a person has too few red blood cells because the cells break apart easily (hemolytic anemia). This is an inherited condition that is most common in people from tropical Africa, the Mediterranean, and certain parts of Asia. It is also common in black Americans.

Certain medications and infections can cause attacks of anemia in people with this condition. For some people, eating fava beans (also called broad beans) can cause an anemic attack.