A carcinogen is any substance that has the potential to cause cancer in living tissues. Carcinogen exposure can occur from the inhalation, ingestion, or absorption of many different types of substances into our bodies. Carcinogens act on our DNA, causing dangerous changes at the cellular level. These include a change in the rate of cell division, which increases the probability of abnormal DNA synthesis. This can lead to cancer, a group of diseases involving abnormal cell growth with the potential to metastasize or spread to other parts of the body.