A free radical is a molecule with an unpaired electron. The molecule is reactive and seeks another electron to pair.  Free radicals are involved in the mechanisms of damage associated with disease development. Examples are hydrogen peroxide, hypochlorite, nitric oxide and nitrogen dioxide. 
The need for antioxidants in peoples’ daily life is becoming more critical with increased exposure to free radicals. Pollution, cigarette smoke, drugs, illness[source?] and stress can increase our exposure.
References[change | change source]
- Afzal, M., Armstrong, D. (2002). “Fractionation of herbal medicine for identifying antioxidant activity”. In: Armstrong, D. (Ed.) Methods in Molecular Biology, vol. 186: Oxidative Stress Biomarkers and Antioxidant Protocols, Humana Press Inc.
- Rice-Evans, C. (1999). “Screening of phenolics and flavonoids for antioxidant activity”. In: Antioxidant Food Supplements in Human Health. Academic Press, p. 239–253.
- Percival, M. (1998). “Antioxidants”. Clinical Nutrition Insights 1/96 Rev. 10/98. http://acudoc.com/Antioxidants.PDF