A free radical is an atom or molecule that has an unpaired electron, making it highly reactive. These unstable particles can damage cells by stealing electrons from other molecules, leading to a chain reaction of instability. Free radicals are produced naturally in the body during processes like metabolism, but they can also come from external sources such as pollution, radiation, and cigarette smoke. The body has natural defenses against free radicals, including antioxidants, which are substances that can donate an electron without becoming unstable themselves. Common antioxidants include vitamins C and E, as well as compounds found in fruits and vegetables. Maintaining a balance between free radicals and antioxidants is essential for overall health.