Cancer occurs when the cells begin to grow out of control. Although the cause of many cancers is unknown, it is known that a small group is due to genetic predisposition.
Most cancers are attributed to substances or external agents called carcinogens, these include:
1) Physical carcinogens such as ultraviolet radiation and X rays.
2) Chemical carcinogens which are related to industrial activities among them: asbestos, arsenic, benzene, cadmium, mercury and lead.
3) Biological carcinogens such as infections caused by certain viruses and bacteria or parasites.
