Free radical theory of aging

The free radical theory of aging was proposed by Denham Harman in 1956. It originally blamed aging on one thing. That is the cumulative damage to your cells from oxygen-derived free radicals. The reasoning drew on 'rate-of-living' and oxygen-toxicity ideas. Harman's 1972 update went further. Called the mitochondrial free radical theory of aging (MFRTA), it pinned the blame on mitochondrial ROS and mtDNA. Oxidative damage is undeniably involved. But large antioxidant trials mostly failed. So the theory is now seen as only partial. Modern frameworks fold it together with mitochondrial dysfunction and redox signaling.

Last reviewed: June 22, 2026

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