What is radon?

How and where does this radioactive noble gas form? How does radon spread?

Radon is a radioactive inert gas occurring naturally in the ground

Radon is an element in the decay chain of uranium, which is ubiquitous in the ground. The natural decay of uranium gives rise to products including radium and radon. Radon gas atoms can in turn disintegrate, producing polonium, bismuth and lead. These decay products, which are also radioactive, attach themselves to airborne particles and tend to accumulate in enclosed spaces. When inhaled, they can be deposited in the lungs and irradiate lung tissue, possibly leading to lung cancer.

How radon spreads

Roter Schleier vor Häusern

The more permeable the ground, the more readily radon gas can rise to the surface. High permeability is found with the smallest (pores) or larger cavities (cracks, fissures, masses of debris or fallen rocks) and in karstic zones and cave systems. Layers of dense clay are scarcely permeable to radon.

Local differences, therefore, are highly marked. In Switzerland, areas with elevated radon concentrations are mainly found in the Alps and the Jura. In some cases, however, high concentrations have also been found in buildings on the Central Plateau. Thus, radon may be found anywhere.

Decay chain of uranium

Decay chain of uranium

Last modification 13.02.2019

Top of page


Federal Office of Public Health FOPH
Division of Radiological
Radiological Risk Section
Schwarzenburgstrasse 157
3003 Berne
Tel. +41 58 464 68 80

Print contact