The causes of cancer include tobacco use, exposure to ultraviolet rays, genetics, and exposure to harmful chemicals, according to the American Cancer Society. Diet and exercise habits may also linked to cancer.
Tobacco products contain poisons that damage the DNA in the cells. When DNA becomes damaged, the cells may grow uncontrollably and form tumors. These poisons also make it difficult for the immune system to fight cancer, according to the Centers for Disease Control and Prevention.
The sun produces two types of ultraviolet radiation: UVA and UVB. UVA rays are not as intense as UVB rays, but they can penetrate glass. This means people are exposed to UVA rays indoors as well as outdoors, according to the Skin Cancer Foundation. Exposure to UV radiation causes cellular damage that can eventually lead to cancer.
Some genetic mutations make it more likely someone will develop cancer. Mutations prevent proteins from working properly or prevent cells from producing the proteins they need to function normally, according to Genetics Home Reference. Not everyone with a genetic mutation will develop cancer, however.
Some cancers are caused by exposure to substances known as carcinogens. Chemicals classified as carcinogens include benzene, arsenic, vinyl chloride, formaldehyde and asbestos, according to Physicians for Social Responsibility.