Carcinogens are substances that can lead to cancer by causing changes in the DNA of cells. These changes can disrupt normal cell growth and division, leading to uncontrolled cell growth, which is a hallmark of cancer. Common carcinogens include certain chemicals, like those found in tobacco smoke, as well as radiation and some viruses, such as the human papillomavirus (HPV). Not all carcinogens are equally dangerous, and exposure levels matter. For example, while asbestos is a known carcinogen linked to lung cancer, not everyone exposed to it will develop cancer. Understanding carcinogens helps us make informed choices about our health and reduce cancer risks.