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Several factors are known to produce cancerous growth in tissues. These are collectively called as Carcinogens. Some of the factors/agents of cancer are described below:

1. Physical agents:

  • Radiations such as X-rays, UV rays, nuclear disasters can cause cancer in human beings.
  • Prolonged exposure to sunlight causes skin cancer.

2. Chemical agents:

  • Mainly include hydrocarbons, soot, coal tar, mustard gas, nicotine smoke, phenolic compounds  arsenic and heavy metal ions.
  • Chewing of tobacco and cigarette smoking causes cancer of lungs, pharynx, pancreas, kidney and oesophagus.
  • Cigarette contains carcinogenic agents such as benzopyrene and N-nitrosodimethylamine.
  • Alcohol consumption causes liver, oesophagus and rectal cancer.

3. Biological agents:

  • Oncogenic viruses are cancer causing viruses.
  • Human papilloma virus (HPV) causes cancer of cervix in females.
  • HIV also causes a particular type of cancer called Kaposi Sarcoma.
  • Epstein Barr virus (EBV) causes nasopharyngeal carcinoma.

4. Dietary factors:

  • Consumption of smoked fish causes stomach cancer.
  • Consumption of fatty foods causes breast cancer.
  • Consumption of beef causes intestinal cancer.

5. Genetic factors:

  • Genetic changes resulting from mutation or presence of virus alters the cell, so that it divides uncontrollably.
  • Retinoblastoma (eye tumour) occurring in children is an inherited type of cancer.