In biology, an adduct is a complex that forms when a chemical binds to a
biological molecule, such as DNA or protein.
DNA adducts are altered forms of DNA that occur as the result of exposure to
carcinogens (in the case of smokers these would be the carcinogens present in
cigarette smoke). A DNA adduct, once formed, can be repaired, resulting in a
return to the original DNA structure or be mis-repaired, resulting in a
mutation. Protein adducts do not have adverse biological effects but can be used
as a measure of exposure to a foreign substance.