A mutagen is any physical or chemical substance that has the ability to alter the genetic material of an organism. This genetic material, known as DNA, contains the instructions that govern the growth, development, and functioning of cells. When a mutagen interacts with DNA, it can cause changes, or mutations, to occur. Mutations can be harmful, beneficial, or have no effect on an organism. In the case of cancer, mutations are often an early step in the development of the disease. Mutagens can be found in a variety of sources, including environmental pollutants, radiation, and certain chemicals. Understanding the effects of mutagens on DNA is crucial to protecting human health and preventing disease.