Aplastic anemia is a rare but serious blood disorder that occurs when the bone marrow cannot make enough new blood cells and platelets. This condition can develop suddenly or slowly, and it can be mild or severe. The symptoms of aplastic anemia can include fatigue, weakness, dizziness, shortness of breath, easy bruising or bleeding, and an increased risk of infections and uncontrolled bleeding. Aplastic anemia can be caused by autoimmune disorders, certain inherited gene changes, toxic substances, radiation therapy, chemotherapy, certain medicines, viral infections, and pregnancy. In some cases, the cause is unknown. Treatment for aplastic anemia might include medications, blood transfusions, or a stem cell transplant, also known as a bone marrow transplant.