The common of all known cause of aplastic anaemia
is exposure to drugs or environmental toxins. Benzene was the first known toxin to cause bone marrow failure. Despite this it is still widely used in industry in the manufacture of drugs, dyes, explosives and other chemicals. Exposure should be limited to 1 part per million, but this is often exceeded, especially in developing countries. Other related organic chemicals also cause aplastic anaemia
toluene (in glues)
the insecticides DDT and lindane
the explosive TNT
the wood preservative PCP
Drugs that cause aplastic anaemia may also be related to benzene. The antibiotic, chloramphenicol and the anti-inflammatory, phenylbutazone are two examples. Neither is commonly used in Western countries, but because they are cheap to produce, they are in widespread use in the developing world. Other medicines with a moderate risk of aplastic anaemia include gold salts and penicillamine, used to treat arthritis, carbamazepine and phenytoin, used to treat epilepsy, and the diuretic acetazolamide.
A large number of drugs have been associated with occasional cases of aplastic anaemia. Most of these are useful drugs and cannot easily be replaced other then turning to herbal medicine.
Radiotherapy (treatment with X-rays) suppresses the bone marrow, and may be intentionally used to do so in preparation for bone marrow transplantation. The use of these treatments should be confined to specialised centres where careful monitoring of the blood count takes place.
Some cases of aplastic anaemia have occurred after viral infections. In particular, hepatitis A, hepatitis B and 'non-A, non-B, non-C' hepatitis have been implicated, and more rarely the Epstein-Barr virus.
Very rarely aplastic anaemia occurs during pregnancy. It is not clear whether this is just a coincidence. Sometimes the disease recovers spontaneously at the end of pregnancy.