Unstable molecules formed as byproducts of the body’s normal chemical processes. In excess, oxygen free radicals can damage cell membranes disrupt the immune system, and contribute to the development of diseases such as cancer, cataracts, and heart disease. The supply of oxygen free radicals in the body can be increased by factors such as smoking, stress, exposure to radiation, inflammation, and air pollution. Antioxidant vitamins such as vitamins A, C, and E are scavengers of oxygen free radicals. To include antioxidants in their diet, people are advised to include plenty of fruit, vegetables, and whole grains.