Sickle cell disease is a blood disease. Instead of red blood cells containing normal hemoglobin, they contain sickle hemoglobin.
Sickle hemoglobin makes red blood cells stiff and sticky.
This leads to anemia and blockage of blood vessels. Sickle cell disease is inherited. In other words, you are born with it. You cannot outgrow sickle cell disease. Problems caused by sickle cell disease may come and go, but the disease itself does not go away.