Cancer is a disease in which normal cells are damaged and do not undergo programmed cell death as fast as they divide via mitosis. Carcinogens increase the risk of cancer by changes in cellular metabolism or damaging DNA directly in cells and it also interfere with biological processes and induce the uncontrolled malignant division leading to the formation oftumors. Usually, severe DNA damage leads to programmed cell death, but if the programmed cell death pathway is damaged, then the cell cannot prevent itself from becoming a cancer cell.
There are many natural carcinogens. Aflatoxin B1, produced by the fungus Aspergillusflavus is an example of naturally occurring microbial carcinogen. Some viruses such as hepatitis B and human papilloma virus, found to cause cancer in humans. Other infectious organisms which cause cancer in humans include some bacteria (e.g. Helicobacterpylori) and helminths (e.g. Opisthorchisviverrini and Clonorchissinensis).
Dioxins and dioxin-like compounds, benzene, kepone, EDB, and asbestos are considered as carcinogenic. Industrial smoke and tobacco smoke were sources of carcinogens. Benzo[a]pyrene, tobacco-specific nitrosamines such as nitrosonornicotine, and reactive aldehydes such as formaldehyde is also a hazardous. Vinyl chloride, from which PVC is manufactured, is a carcinogen and thus a hazard in PVC production.
