Rutin is a phenolic antioxidant and has been demonstrated to scavenge superoxide radicals. Rutin can chelate metal ions, such as ferrous cations. Ferrous cations are involved in the so-called Fenton reaction, which generates reactive oxygen species. Rutin may also modulate the respiratory burst of neutrophils. The in vivo antioxidant activity of rutin is most likely due to its aglycone quercetin, to which it is metabolized following ingestion. Although most studies show rutin to inhibit lipid peroxidation, a few studies do not. Rutin may also help maintain levels of the biological antioxidant reduced glutathione. Importantly, under certain conditions, rutin or its metabolite quercetin may become a pro-oxidant. For example, nitrosation of rutin/ quercetin may produce a pro-oxidant molecule that may have mutagenic potential.