Explain the causes of cancer.

Explanation

Cancer causing agents are called carcinogens. They are physical, chemical agents, ionizing radiations and biological agents.
(i) Physical Irritant : Heavy smoking causes lung cancer and cancers of oral cavity, pharynx (throat) and larynx. Betel and tobacco chewing causes oral cancer, Excessive exposure to sunlight may cause skin cancer.
(ii) Chemical agents : Nicotine, caffeine, products of combustion of coal and oil, pesticides, asbestos, nickel, certain dyes and artificial sweetners induce cancer.
(iii) Radiations : Ionizing radiations like X-rays, gamma-rays, radioactive substances and non-ionising radiations like UV rays cause DNA damage leading to cancer.
(iv) Biological agents : Cancer causing viruses are called oncogenic viruses.