A mutagen is any agent (physical, chemical, or biological) capable of altering the structure of DNA within human cells. This program explores how some mutations are a natural process resulting from errors in the copying and repair of DNA and how some mutagens naturally exist in the world (e.g., UV radiation, cosmic rays, and some radioactive isotopes). Others are specific chemicals that have been synthesized for use in manufacturing or other industries. Mutagens may also arise during the metabolism of certain foods. In many cases mutagens may also lead to the development of cancers.