mutagen

thumb|The Globally Harmonized System of Classification and Labeling of Chemicals|international pictogram for chemicals that are sensitising, mutagenic, [[carcinogenic or toxic to reproduction]]

In genetics, a mutagen is a physical or chemical agent that permanently changes genetic material, usually DNA, in an organism and thus increases the frequency of mutations above the natural background level. As many mutations can cause cancer in animals, such mutagens can therefore be carcinogens, although not all necessarily are. All mutagens have characteristic mutational signatures with some chemicals becoming mutagenic through cellular processes.