Your Atoms Turn Over Constantly, By Evaporation Rather Than Tunnelling

Your body's atoms really are replaced continuously — but the mechanism is ordinary thermodynamics, not anything quantum, and the popular figures deserve care. ## The mechanisms **Evaporation and respiration.** Water leaves through the skin and lungs constantly. Insensible losses — evaporation you never notice, without visible sweating — run to several hundred grams a day from respiration alone. Every exhaled breath removes carbon as CO₂ that was recently part of your tissue. **Shedding.** The outer skin layer is continuously lost, and the gut lining is replaced on a scale of days. **Metabolic turnover.** Proteins are degraded and resynthesised continuously, with half-lives from minutes to years depending on the protein. Atoms cycle through structures rather than sitting in them. ## About the "98% of your atoms every year" figure This number circulates widely and should be treated as a rough illustration rather than a measurement. It appears to descend from mid-twentieth-century isotope tracer work, and the underlying reality is that **turnover rates vary enormously by tissue**: - Gut lining epithelium: days - Red blood cells: about four months - Skeletal muscle: on the order of a decade or more - Bone mineral: years, with a slow ongoing exchange - Some structures barely turn over at all — carbon-14 dating of tissue has been used to show that the cells of the cerebral cortex and the lens crystallins of the eye are largely as old as the person So "you are a new person every seven years" or "98% per year" are not accurate as stated. The defensible version is that most of your body's matter is in continuous flux while some structures persist for a lifetime. ## Not tunnelling, and not radioactivity either Two conflations are worth separating. **Not tunnelling.** Atoms leaving the body are leaving by desorption, evaporation and shedding — thermal processes with energy barriers of order an eV, crossed constantly at body temperature. Loss by tunnelling into a floor is not merely negligible but astronomically so. See Can You Tunnel Through the Floor? The Compound Probability and the Barrier Maths. **Not radioactive decay either.** A human body undergoes roughly 7,000–8,000 radioactive decays per second, mostly from potassium-40 and carbon-14. That sounds like continuous disintegration but it is a vanishing fraction of the body's atoms, and those decays are beta emission and electron capture — weak-interaction processes, not tunnelling. See Alpha Decay: Gamow's 1928 Tunnelling Explanation. The honest summary: you shed atoms constantly, at a rate that makes tunnelling irrelevant by something like two hundred orders of magnitude, and the interesting question was never whether you lose atoms but by what route.