Carcinogen is a cancer-causing agent. Cellular metabolism is changed due to carcinogens or DNA is harmed in cells thus affecting the natural process and causing cancer. The best example of a carcinogen is Aflatoxin B1, which is found on grains, nuts and peanut butter.

Carcinogens can also be formed if protein-rich foods are cooked at high temperatures. Their level of harmfulness is same as in cigarette smoke which contains benzopyrene. Carcinogens can be reduced if meat is cooked in microwave oven for some time before broiling or barbecuing it.

Benzene and asbestos are the well-known carcinogens while kepone and EDB are lesser known. Many carcinogens, including benzopyrene, could be found in industrial and tobacco smoke.

Vinyl chloride found in PVC too is a carcinogen. Cancer in humans could also be caused by viruses like Hepatitis B. Rous sarcoma virus was the first virus that resulted to cancer in animals. Peyton Rous discovered this cancer-causing virus in 1910.

All radionuclides can cause cancer but the extent of its harm can be determined by the kind of radiation alpha, beta or gama rays emit and the magnitude of its exposure.

For example, Thorotrast, which is found in x-ray diagnostics, can be very harmful carcinogen at it is retained within organs and its emits alpha particles. Exposure to radiation while experimenting led to the death of Wilhelm Rontgen and Marie Curie who died of cancer.

Acrylamide found in fried or overcooked carbohydrate foods for example french fries is also a carcinogen. Its potential risk is being assessed.

Carcinogens can be classified into various groups:

• Group 1 – this includes substances which causes cancer in human beings.
• Group 2A – this group includes agents which can cause cancers in humans.
• Group 2B – this group includes substances that could possibly cause cancer..
• Group 3 – agents in this group do not cause cancer to humans but they could cause cancer among animals.
• Group 4 – substances in this group are not likely to cause cancer in humans.