Free radicals

Free radicals are atoms or molecules carrying one or more unpaired electrons, which makes them highly reactive. They arise from normal metabolism, immune activity, and external sources such as UV radiation, pollution, and tobacco smoke. By stealing electrons from neighbouring molecules, free radicals damage membranes, enzymes, and DNA. The free-radical theory of ageing posits that this cumulative damage contributes to functional decline and age-related disease; though historically influential, the theory is now considered an incomplete account of ageing, as supplemental antioxidants have not reliably extended lifespan in animal trials or human RCTs, and reactive oxygen species are increasingly recognised as signalling molecules as well as damaging agents.