Reactive oxygen species (ROS), such as hydroxyl and superoxide radicals, singlet oxygen, and hydrogen peroxide, are byproducts of metabolic processes in the body and play an important role in regulating cell physiology and function. But uncontrolled ROS formation (oxidative stress) can result in DNA, protein, and lipid damage, which has been implicated in several diseases, including cancer. Antioxidants, produced endogenously or in supplemental form, function as ROS scavengers and inhibit oxidative stress. Popular antioxidants include vitamins C and E, selenium, beta carotene, lycopene, resveratrol, flavonoids, anthocyanins, and catechins. They are widely used to prevent cancer and its recurrence.