There are three main varieties of tea -- green, black, and oolong. The difference is in how the teas are processed. Green tea is made from unfermented leaves and reportedly contains the highest concentration of powerful antioxidants called polyphenols. Antioxidants are substances that fight free radicals -- damaging compounds in the body that change cells, damage DNA, and even cause cell death. Many scientists believe that free radicals contribute to the aging process as well as the development of a number of health problems, including cancer and heart disease. Antioxidants such as polyphenols in green tea can neutralize free radicals and may reduce or even help prevent some of the damage they cause.