Radon

Radon is produced by the decay of uranium in rock and soil and accumulates indoors, particularly in poorly ventilated ground floors and basements; levels depend on local geology, so neighbouring streets can differ. Cancer Research UK attributes 5 percent of UK lung cancer cases to ionising radiation as a whole, of which indoor radon is the largest component, and reports an estimated 9 percent of European lung cancer deaths as linked to indoor radon. The dose-response is close to linear with no safe threshold: pooled analyses put lung cancer risk 16 percent higher per 100 becquerels per cubic metre of usual home radon level. Risk multiplies with smoking rather than adding to it, so radon causes far more cancers in people who smoke than in people who do not, while remaining one of the few known causes of lung cancer in never-smokers. It is measurable and it is fixable: detectors are left in a house for months and returned by post, and remediation is a matter of sealing entry points, improving underfloor ventilation and, where needed, fitting a sump and fan. This makes radon one of the small number of lung cancer risks that a household can act on directly.