A mutagen is any substance or agent that can cause a mutation, or change in the sequence or structure of DNA. Mutagens are classified on the basis of their physical nature and the types of damage they do. A mutagen is not the same as a carcinogen. Carcinogens are agents that cause cancer. While many mutagens are carcinogens as well, many others are not. The Ames test is a widely used test to screen chemicals used in foods or medications for mutagenic potential.

Chemical Mutagens

There are many hundreds of known chemical mutagens. Some resemble the bases found in normal DNA; others alter the structures of existing bases; others insert themselves in the helix between bases; while others work indirectly, creating reactive compounds that directly damage the DNA structure.

"Base analogs" are molecules whose chemical structure is similar to one of the four DNA bases (adenine, thymine, cytosine...