Posted: 21 August 2000

A chemical or physical agent capable of causing cancer. Human activities can introduce chemical carcinogens such as chlorinated hydrocarbons or physical carcinogens such as asbestos or ionising radiation into the environment, but natural carcinogens such as toxic metals beryllium (Be), cadmium (Cd) and selenium (Se) are also present. There are two types of carcinogens: DNA-reactive carcinogens that alter the DNA of cells, and epigenetic carcinogens that do not react with DNA but may alter the immune system, cause hormonal imbalances or cause chronic tissue injury, all of which could lead to cancer. Carcinogens may be inhaled, ingested or absorbed through the skin.