Free radicals are oxygen-containing chemicals that have an impaired electron. The impaired electron makes free radicals highly reactive to DNA, proteins, membranes, and other cell machineries, resulting in oxidative damages including DNA mutations, protein dysfunction, and destruction of membrane and other cell structures. These oxidative damages promote aging and increase the risk of age-related diseases such as cancer, cardiovascular diseases, immune system declines, brain dysfunction, and cataracts. Known free radicals that are involved in the aging process are superoxide, hydrogen peroxide (H2O2), hydroxyl radical (OH), singlet oxygen, lipid epoxides, lipid hydroperoxides, lipid alkoyl, peroxyl radicals, and oxides. They are either produced during our normal metabolisms or introduced into our bodies from outside sources