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As suggested by the name, these atoms and molecules — also known as oxidants — have a “free,” unpaired electron. These spare electrons make the atoms unstable and highly susceptible to chemical reactions with other more stable atoms.
Because atoms want to be stable, those that aren’t will seek out the electron they require to make a pair, even if that means taking it from another molecule. Sometimes, this alteration of the “donor” atom can turn it into another free radical, which repeats the electron-robbing process. This eventually can cause tissue damage and is thought to contribute to a range of health effects including aging, heart disease, cancer and mental disorders such as Parkinson’s and Alzheimer’s disease.
The body is equipped with tools called antioxidant systems to keep free radicals in check, but stress, aging, pollution and cigarette smoke, among other things, can introduce additional free radicals and upset that balance. Foods like tomatoes, citrus fruits, fish and dark-green vegetables are good sources of antioxidants and can help keep free radicals at a healthy level.