Sir Percivall Pott (1714-1788) was the first to discover that certain substances present in our environment can cause cancer. Such substances were named as carcinogens.

What are Carcinogens?
Carcinogens are defined as any such biological, chemical or physical agents that may cause cancer. Not all carcinogens can cause cancer all the time. This is because different carcinogens have different levels of abilities to cause cancer. The risk of developing cancer depends on factors such as a person’s genetic makeup, how long he is exposed to a particular carcinogen, intensity of exposure, etc.

Carcinogens in Prepared Food
Food cooked at high temperature can lead to the formation of many potent carcinogens. Some of these carcinogens originate from reaction between proteins and carbohydrates and / or creatine. Few such carcinogens are polycyclic aromatic hydrocarbons (PAH), acrylamide, heterocyclicamines (HCA), etc. People can get exposed to PAH by eating charred or grilled meat, contaminated flour, bread, fruits, meat, cereals, etc.

Carcinogens in Cigarettes
It is estimated that nearly 30% of all cancer deaths can be directly linked with use of tobacco. Some carcinogens in tobacco include nicotine, carbon monoxide, ammonia, formaldehyde, hydrocyanic acid, arsenic, lead, etc. Tobacco smoking can cause lung cancer, cardiovascular disease, emphysema, etc.

Environmental Carcinogens
There are several environmental factors that can expose us to various types of carcinogens. Some such factors are diet, smoking, infectious diseases, radiations, chemicals, etc.

Chemical Carcinogens
There are many chemicals that can cause cancer in human beings or animals after continued or excessive exposure. For example, exposure to fumes of nickel, cadmium and chromium can cause lung cancer. Skin and lung cancer can be caused by exposure to arsenic. Liver sarcomas can cause because of exposure to vinyl chloride.

Infectious Diseases and Cancer
It has recently been found that certain bacteria, viruses and parasites can cause several types of cancer in humans. About 15%-20% of cancers are linked with infections. Some such cancer-causing organisms are Human papilloma viruses (HPV, cervical cancer), Epstein-Barr virus (EBV, nasopharyngeal cancer), Helicobacter pylori (stomach cancer), etc.

How Carcinogens are Classified?
The International Agency for Research on Cancer (IARC) has classified carcinogens by placing them into the following categories:

Group 1: These include agents that are definitely carcinogenic to human beings.
Group 2A: These include such agents that are probably carcinogenic to humans.
Group 2B: These include such agents that are possibly carcinogenic to humans.
Group 3: These include such agents that are unclassifiable as to carcinogenicity to humans.
Group 4: These include agents that are probably not carcinogenic to humans.