The term “oxidative stress” refers to the presence of excessive levels of highly reactive molecules called free radicals in the cell or a lack of molecules called antioxidants that can eliminate those free radicals.

An excess of free radicals can cause damage to tissue and other components of the body such as DNA by "oxidizing" them (the same chemical reaction that causes iron to rust). Oxidative stress can also cause reduced immune function and increased risk of other chronic condition including aging.