1) Damage to biological tissues caused by superoxide and other free radicals generated as a result of intoxication, antimicrobial cellular immunity, metabolic abnormality, or "normal" aging; do not confuse with hypoxia or hyperoxia.

2) Physiological stress on the body that is caused by the cumulative damage done by free radicals inadequately neutralized by antioxidants and that is held to be associated with aging.