A type of unstable molecule that is made during normal cell metabolism (chemical changes that take place in a cell). Free radicals can build up in cells and cause damage to other molecules, such as DNA, lipids, and proteins. This damage may increase the risk of cancer and other diseases.

An unstable molecule in the body that plays a role in aging and can damage tissue; antioxidants help prevent free radical damage.

Chemicals whose molecular or ionic structure includes an unpaired ("free") electron, usually conferring high reactivity; in biological systems, most free radicals contain oxygen (prefer FREE RADICAL OXYGEN).

Molecules or atoms with at least one unpaired or 'free' electron in the outermost electron shell. Chemically unstable, free radicals stabilize themselves by appropriating an electron from a nearby molecule, thereby damaging that molecule by altering the electron number in its outermost electron shell. By-products of both normal cell processes and environmental toxin exposure, oxygen free-radicals in high concentrations may damage DNA, proteins, and lipids, thereby increasing the risk for various diseases including cancer. (NCI04)

Highly reactive molecules with an unsatisfied electron valence pair. Free radicals are produced in both normal and pathological processes. They are proven or suspected agents of tissue damage in a wide variety of circumstances including radiation, damage from environment chemicals, and aging. Natural and pharmacological prevention of free radical damage is being actively investigated.