A carcinogen is any substance or agent that can cause cancer in living tissue. Carcinogens can be found in various forms, including chemicals, radiation, and certain viruses. They can damage the DNA in cells, leading to uncontrolled cell growth and tumor formation. Common examples of carcinogens include tobacco smoke, asbestos, and ultraviolet (UV) radiation from the sun. Exposure to carcinogens can occur through various routes, such as inhalation, ingestion, or skin contact. Regulatory agencies, like the International Agency for Research on Cancer (IARC), classify carcinogens based on their potential risk to humans, helping to inform public health guidelines and safety measures.