The etiology of aplastic anemia is unclear. A more classical theory is the seed, soil, and bug theory. The seed theory suggests that patients with this condition have reduced hematopoietic stem cells in the bone marrow, leading to bone marrow failure. The soil theory refers to abnormal microenvironments in the bone marrow of patients, which leads to an abnormal growth environment for stem cells and consequently hematopoietic disturbances. The bug theory, which is commonly referred to in clinical settings as immune dysfunction, plays a major role in the etiology of this condition.