text: A DNA damaging agent is an agent that causes a change in the structure of DNA that is not itself replicated when the DNA is replicated.  Examples of DNA damage include a chemical addition or disruption of a nucleotide base in DNA (generating an abnormal nucleotide or nucleotide fragment), or a break in one or both strands in DNA.  When duplex DNA containing a damaged base is replicated, an incorrect base may be inserted in the newly synthesized strand opposite the damaged base in the complementary template strand, and this can become a mutation in the next round of replication.  Also a DNA double-strand break may be repaired by an inaccurate process leading to an altered base pair, a mutation.  However, mutations and DNA damages differ in a fundamental way: mutations can, in principle, be replicated when DNA replicates, whereas DNA damages are not replicated.  Thus DNA damaging agents often cause mutations as a secondary consequence, but not all DNA damages lead to mutation and not all mutations arise from a DNA damage.  The term genotoxic means toxic (damaging) to DNA.