Ionizing radiation is radiation that has sufficient energy to ionize atoms or molecules, i.e. to eject electrons from their atomic shell. In the cells of organisms, ionizing radiation can lead to changes in the DNA or cell death, or both. At high doses, such cell killing can damage organs and lead to so-called deterministic health effects, such as acute radiation syndrome or skin burns. On the other hand, damage to the DNA of surviving cells can lead to so called stochastic effects including cancer. It is widely assumed that cancer risks increase linearly with radiation dose and that there is no threshold below which effects can be excluded. This assumption is referred to as the linear no threshold model (LNT) and is used in radiological protection for calculating effects of exposure to low doses of radiation on cancer risks. Because these effects are expected to be small, they are difficult to measure in epidemiological studies.
For more information on health effects of ionizing radiation you can visit the page of the Federal Office of Public Health.
The average exposure to ionizing radiation for the Swiss population is about 5.8 mSv per year. With 3.2 mSv/y Radon is the most important contributor, however, as Radon decays through the alpha decay, the dose from Radon mainly goes to the lung and to the skin. The next important contribution comes from diagnostic medical procedures (1.4 mSv), cosmic (0.4 mSv) and terrestrial (0.35 mSv) radiation and ingestion (0.35 mSv). Other sources contribute an additional 0.1 mSv/y .
Map of terrestrial and cosmic radiation in Switzerland based on a model by Rybach et al. 2002 
Here you can read more on the different components of radiation exposure in Switzerland and how these are measured.
More information about:
Yearly report on environmental radioactivity and radiation exposure, FOPH (german): https://www.bag.admin.ch/bag/de/home/das-bag/publikationen/taetigkeitsberichte/jahresberichte-umweltradioaktiviaet.html
Albert Gockel and cosmic radiation (in German): https://www.sps.ch/artikel/physik_anekdoten/zwei_pioniere_auf_dem_gebiet_kosmische_strahlung_6/albert_gockel_und_die_kosmische_strahlung/
1 Bundesamt für Gesundheit. Umweltradioaktivität und Strahlendosen in der Schweiz, Jahresbericht 2017. Bundesamt für Gesundheit BAG, Abteilung Strahlenschutz, Schweizerische Eidgenossenschaft; 2018.
2 Rybach L, Bachler D, Bucher B, Schwarz G. Radiation doses of Swiss population from external sources. J Environ Radioact. 2002;62(3):277-86.