||An atom or molecule made in the body that can damage cells. A free radical has at least one unpaired electron, which makes it unstable. To become stable, the free radical takes an electron away from another atom, which makes that atom unstable, and starts a chain reaction that can injure cells. Free radicals are made during chemical changes that take place in a cell or an organism to produce energy and basic materials needed for important life processes (metabolism). They also come from tobacco smoke, pollution, radiation from the sun and x-rays, and other sources outside the body. Free radicals damage cells, cause genetic alterations (mutations), and may play a role in cancer, heart disease, and age-related diseases (such as Alzheimerâ€™s, Parkinsonâ€™s, and Lou Gehrigâ€™s diseases). Free radicals are also beneficial; they are involved in killing germs (microorganisms) and they help hormones and chemical messengers communicate with cells. Proteins (enzymes) made by the body, and vitamin C, vitamin E, and beta carotene in the diet help prevent free radical damage.