Leukemia is more often occurs in males than in females and in white population more than black. The actual causes of leukemia is unknown but research has found certain risk factors that increase a person's chance of developing leukemia.

The rick factors are :

Exposure to high doses of radiation such as by atomic bomb explosions (such as those in Japan during World War II) and nuclear power plant accidents (such as the Chernobyl accident in 1986). Also in medical treatment using radiation therapy.
Exposure to electromagnetic fields.
Genetic disorders like Fanconi anemia, Schwachman-Diamond syndrome and Down syndrome.
Workers exposed to certain chemicals like benzene, formaldehyde over a long period of time can cause leukemia
People with myelodysplasic syndrome (a blood disorder) are at increased risk of developing acute myeloid leukemia.
Some cancer-fighting drugs used in the treatment of other types of cancer sometimes later develop leukemia
Human T-cell leukemia virus-I (HTLV-I) can causes human T-cell leukemia
Smoking is also a risk factor.