Sickle cell anemia is an inherited form of anemia — a condition in which there aren’t enough healthy red blood cells to carry adequate oxygen throughout your body.
Normally, your red blood cells are flexible and round, moving easily through your blood vessels. In sickle cell anemia, the red blood cells become rigid and sticky and are shaped like sickles or crescent moons. These irregularly shaped cells can get stuck in small blood vessels, which can slow or block blood flow and oxygen to parts of the body.
Read more at the Mayo Clinic