Aplastic anemia is a blood disorder in which the body's bone marrow doesn't make enough new blood cells. Bone marrow is a sponge-like tissue inside the bones. It makes stem cells that develop into red blood cells, white blood cells, and platelets. Red blood cells carry oxygen to all parts of your body. They also carry carbon dioxide (a waste product) to your lungs to be exhaled. White blood cells help your body fight infections. Platelets are blood cell fragments that stick together to seal small cuts or breaks on blood vessel walls and stop bleeding. In people who have aplastic anemia, the body doesn't make enough red blood cells, white blood cells, and platelets. This is because the bone marrow's stem cells are damaged. (Aplastic anemia also is called bone marrow failure.)