Health
Group 1 carcinogen (IARC)
The highest classification of the International Agency for Research on Cancer, reserved for agents with sufficient evidence of carcinogenicity in humans. Radon has been classified as a Group 1 carcinogen since 1988, based on studies of miners and residential epidemiology.
Related terms
Radon progeny (decay products)The short-lived radioactive isotopes (polonium, lead, bismuth) produced when radon decays. Attached to aerosols, they are inhaled and lodge in the airways, where their alpha emissions irradiate lung tissue — they, rather than radon gas itself, deliver most of the dose.Alpha radiationIonizing radiation consisting of helium nuclei emitted by radon and its progeny. Alpha particles travel only micrometres in tissue but deposit their energy densely, which makes inhaled alpha emitters particularly damaging to the cells lining the lungs.Radon and smoking (combined risk)Tobacco smoke and radon multiply rather than merely add their effects: at the same radon level, the absolute lung cancer risk of a smoker is many times that of a never-smoker. Quitting smoking and reducing radon together provide the largest risk reduction.Radon lung cancer riskThe probability of developing lung cancer from radon exposure, which grows roughly linearly with concentration and duration — pooled European studies estimate about 16% higher risk per 100 Bq/m³ of long-term exposure. The WHO attributes 3–14% of lung cancers to radon depending on the country.