Aplastic anemia symptoms may include:

• Fatigue

• Shortness of breath with exertion

• Rapid or irregular heart rate

• Pale skin

• Frequent or prolonged infections

• Unexplained or easy bruising

• Nosebleeds and bleeding gums

• Prolonged bleeding from cuts

• Skin rash

• Dizziness

• Headache

Aplastic anemia develops when damage occurs to your bone marrow, slowing or shutting down the production of new blood cells. Bone marrow is a red, spongy material inside your bones that produces stem cells, which give rise to other cells. Stem cells in the bone marrow produce blood cells — red cells, white cells and platelets. In aplastic anemia, the bone marrow is described in medical terms as aplastic or hypoplastic — meaning that it's empty (aplastic) or contains very few blood cells (hypoplastic).

Factors that can temporarily or permanently injure bone marrow and affect blood cell production include:

• Radiation and chemotherapy treatments. While these cancer-fighting therapies kill cancer cells, they can also damage healthy cells, including stem cells in bone marrow. Aplastic anemia can be a temporary side effect of these treatments.

• Exposure to toxic chemicals. Exposure to toxic chemicals, such as some used in pesticides and insecticides, may cause aplastic anemia. Exposure to benzene — an ingredient in gasoline — also has been linked to aplastic anemia. This type of anemia may get better on its own if you avoid repeated exposure to the chemicals that caused your initial illness.

• Use of certain drugs. Some medications, such as those used to treat rheumatoid arthritis and some antibiotics, can cause aplastic anemia.

• Autoimmune disorders. An autoimmune disorder, in which your immune system begins attacking healthy cells, may involve stem cells in your bone marrow.

• A viral infection. Viral infections that affect bone marrow may play a role in the development of aplastic anemia in some people. Viruses that have been linked to the development of aplastic anemia include hepatitis, Epstein-Barr, cytomegalovirus, parvovirus B19 and HIV.

• Pregnancy. Aplastic anemia that occurs in pregnancy may be related to an autoimmune problem — your immune system may attack your bone marrow during pregnancy.

• Unknown factors. In many cases, doctors aren't able to identify the cause of aplastic anemia. This is called idiopathic aplastic anemia.

Confusion with myelodysplastic syndrome

Aplastic anemia can be mistaken for a condition called myelodysplastic syndrome. In this group of disorders, the bone marrow produces new blood cells, but they're deformed and underdeveloped. The bone marrow in myelodysplastic syndrome is sometimes called hyperplastic — meaning that it's packed with blood cells. But some people with myelodysplastic syndrome have empty marrow that's difficult to distinguish from aplastic anemia.

Connections with other rare disorders

Some people with aplastic anemia also have a rare disorder known as paroxysmal nocturnal hemoglobinuria. This disorder causes red blood cells to break down too soon. Paroxysmal nocturnal hemoglobinuria can lead to aplastic anemia, or aplastic anemia can evolve into paroxysmal nocturnal hemoglobinuria.

Fanconi's anemia is a rare, inherited disease that leads to aplastic anemia. Children born with it tend to be smaller than average and have birth defects, such as underdeveloped limbs. The disease is diagnosed with the help of blood tests.

Aplastic anemia is rare. Factors that may increase your risk include:

• Treatment with high-dose radiation or chemotherapy for cancer

• Exposure to toxic chemicals

• The use of some prescription drugs — such as chloramphenicol, which is used to treat bacterial infections, and gold compounds used to treat rheumatoid arthritis

• Certain blood diseases, autoimmune disorders and serious infections

• Pregnancy, rarely