A period of many years usually exists between the initiation of the cancer process and the onset of the symptoms. No one completely understands this process, but certain aspects of a person's lifestyle can be linked to cancer formation. There is no single cause of cancer. Genetic factors by themselves probably account for only a small fraction of cancers. Genetic factors do have an important influence on an individual's chance of developing cancer when combined with outside factors.
Cigarette smoking is the leading cause of cancer.
Portions of the diet, especially fatty foods and alcoholic beverages , also are linked to cancer. Skin exposure to ultraviolet radiation in sunlight is the primary cause of melanoma, a skin cancer. Sexual behavior that helps spread sexually transmitted infections is closely linked to cervical cancer in women. Environmental pollution by chemicals in drinking water, air, food and in the workplace may contribute to cancer. The harmful health effects of chemicals depend on the dose, strength of the chemical compound and the length of exposure.