Radon is a naturally occurring radioactive gas. It has no smell, colour or taste, and is produced from the natural radioactive decay of uranium in rocks and soil. Radon can also be found in water.

Radon gas escapes easily from the ground into the air. Outdoors, radon quickly dilutes to very low concentrations and is generally not a problem. However, it tends to concentrate in enclosed spaces, such as underground mines, houses, and other buildings. Soil gas infiltration is recognized as the most important source of residential radon. Other sources of radon include building materials and water extracted from wells, but are of less importance.

Radon decays and produces further radioactive particles. As we breathe, the particles are deposited on the cells lining the airways, where they can damage DNA and potentially cause lung cancer.

Radon causes between 3–14% of all lung cancers, depending on the average radon level and the smoking prevalence in a country. Radon is much more likely to cause lung cancer in people who smoke: smokers are 25 times more at risk from radon than non-smokers.

For most people, the greatest exposure to radon occurs in the home. The concentration of radon in a home depends on the amount of uranium in the underlying rocks and soils, the construction of the house and the ventilation habits of the inhabitants. 

Radon levels can be measured in an inexpensive and simple manner. 

Well-tested, durable and cost-efficient methods exist for preventing radon in new houses and reducing radon in existing dwellings. Radon prevention should be considered when new houses are built, particularly in radon prone areas. Radon levels in existing homes can be reduced by, for example, improving the ventilation of the house and sealing floors and walls.

In many countries, drinking water is obtained from groundwater sources such as springs and wells. Radon dissolved in drinking-water can be released into indoor air. Normally, a higher radon dose is received from inhaling radon compared with ingestion. Straightforward and effective techniques exist to reduce the concentration of radon in drinking-water supplies by aeration or using special filters.

WHO works with international partners to increase understanding of the effects of radon exposure on health and to promote sound policy options for preventing and mitigating radon exposure. 

WHO supports the development of national radon programmes and activities related to radon policies, radon mitigation and prevention as well as radon risk communication.