Radon is a colourless and odourless noble gas that is present in the indoor air in homes and at workplaces. Approximately two thirds of the annual radiation dose received by Finns results from radon present in indoor air. Long-term exposure to high radon levels in the home considerably increases the risk of lung cancer. In Finland, approximately 300 people each year are diagnosed with radon-induced lung cancer.

Decay products of radon in the air are inhaled into the lungs. They stick to the inner surface of the lungs, emitting alpha radiation. The radiation dose received into the lungs increases the risk of lung cancer. Even a small radiation dose may cause cancer, albeit the probability is low. The longer the stay and the higher the radon level, the higher the risk.

In Finland, 2,000 cases of lung cancer are diagnosed each year, approximately 300 of them associated with exposure to radon. Next to smoking, indoor-air radon is the most important known cause of lung cancer. For smokers, the risk caused by radon is higher than for non-smokers. 

Thus, in a radon concentration of 700 Bq/m³, the smoker’s risk is 2*10%, that is, 20%, and the non-smoker’s risk is also doubled to 1%. The lung cancer risk for a person who has quit smoking is between one and twenty per cent. After quitting smoking, the risk decreases over time.

Table. The number of lung cancer cases resulting from different causes, and the contribution of radon in the radon concentration categories. The national average radon concentration is assumed to be 100 Bq/m3, and the number of annual lung cancer deaths is assumed to be 1,991 (statistics of the Finnish Cancer Registry from 2008). (Source: Mäkeläinen I. Kuka saa syövän radonista? Ympäristö ja terveys 2010: 3; 60–63)

According to current understanding, radon does not cause other health hazards in addition to lung cancer. It does not cause allergic reactions, dizziness, fatigue or other similar sensations. Furthermore, radon does not harm objects or food stored in an environment with a high radon concentration. When an object is taken away from that environment, the radon decay products accumulated on its surface disappear within a few hours. Radon has nothing to do with the phenomenon called earth radiation.