A carcinogen is any substance or agent that can cause cancer in living tissue. These can be chemicals, physical agents like radiation, or biological agents such as certain viruses. Carcinogens can damage the DNA in cells, leading to uncontrolled cell growth and tumor formation. Carcinogens are classified into different categories based on their potential to cause cancer. For example, some well-known carcinogens include tobacco smoke, asbestos, and benzene. Understanding carcinogens is crucial for cancer prevention and public health, as reducing exposure can lower the risk of developing cancer.