In genetics, a
mutagen is a physical or chemical agent that changes the genetic material, usually
DNA, of an
organism and thus increases the frequency of
mutations above the natural background level. As many mutations can cause
cancer, mutagens are therefore also likely to be
carcinogens. Not all mutations are caused by mutagens: so-called "spontaneous mutations" occur due to spontaneous
hydrolysis,
errors in
DNA replication, repair and
recombination.