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Ionising radiation

Environmental Radioactivity - Medicine - Occupational Radiation Protection - Nuclear Hazards Defence

Ionisierende Strahlung

Health effects of indoor radon

  • Radon can accumulate in the ambient air of closed rooms. Particularly harmful are its short-lived progeny which can deposit in the respiratory tract. Alpha radiation that accrues during decay can promote lung cancer.
  • According to statistical risk calculations, nearly 1,900 deaths yearly are due to indoor radon in Germany. Within the European Union, 20,000 deaths yearly can be attributed to indoor radon.
  • A permanently increased radon concentration in ambient air of 100 Becquerel per cubic meter increases the lung cancer risk by about 16 %.

Drawing of radon inside the lung Radon and healthRadon in the human body

The inert gas radon can easily leak from the underground and spread in the air or solute in water. Due to the dilution effect, the radon concentration in free air is very low. In closed rooms, however, radon can accumulate in the air.

Thus, indoor concentrations are usually higher than outdoors and can be extremely high in underground mining. This is the reason why health effects were first observed in miners working underground. Meanwhile, they have also been proven for smaller concentrations possibly occurring in dwellings.

What health risks are associated with radon?

The health risks mainly result not from radon itself, but from its short-lived progeny. Due to its inert gas properties and the half-life of almost 4 days, the largest part of radon is exhaled. The breathing air also contains radon progeny (radioactive isotopes of the elements polonium, bismuth and lead) which are largely bound to the aerosols and dust particles in the air. They deposit in the airways until their complete decay. This decay generates high-energy alpha rays of high biologic effectiveness that hit the radiosensitive cells of the bronchial epithelium.

Alpha radiation can damage the cells and thus promote lung cancer. A small part of the inhaled radon and its progeny can spread via the lungs to the blood and reach other organs. However, the resulting organ doses and the associated cancer risks are very low. So far, the only proven health risk of radon is lung cancer.


As early as in the 16th century, an unusual accumulation of lung cancer was observed in underground miners in Schneeberg in the Ore Mountains and was named "Schneeberg disease". At that time, it was not known that the disease was lung cancer and what was its cause. Four centuries later, it was shown in a series of miners’ studies that radon and its progeny are a causal factor for bronchial carcinoma. The International Association for the Research in Cancer (IARC) of the World Health Organization (WHO) classified radon as a human carcinogen in 1988. As a consequence, the question arose whether also lower concentrations, such as usually found in dwellings, might pose a health risk to the population.

In the 1980s, more than 20 large epidemiologic studies were conducted in Europe, North America and China to directly investigate the lung cancer risk of radon in dwellings. Among them were two large studies from Germany. The studies have meanwhile been finished and published. They consistently show an increased risk of lung cancer from indoor radon. The risk estimates are very similar to those of the miners’ studies at comparable exposures.

European studies on lung cancer and indoor radon

The largest and most valid study is the combined analysis of 13 European studies, published in 2005 (Darby et al. 2005 and Kreuzer 2005). Overall, 7,148 lung cancer cases and 14,208 controls were included. Radon concentrations in the current and past homes of the participants were measured for at least six months. Furthermore, all individuals were questioned in detail about their smoking history and other potential risk factors for lung cancer.

The time-weighted average radon concentration for dwellings of the last 35 years was calculated for each individual. All risk analyses considered the most important confounders such as age, gender, smoking and region.

Risk assessment

The results of the combined analysis of 13 European studies constitute the basis for the re-evaluation of radon-induced health risks by the Federal Office for Radiation Protection (BfS) and the German Commission on Radiation Protection (SSK) in 2005, as well as for the current assessment by WHO (WHO, 2009). We present a summary of the results here.


According to the present results, radon is considered a cause of lung cancer in smokers and non-smokers.


The association between radon exposure and lung cancer risk is linear without indication for a threshold, meaning that the lung cancer risk increases proportional with increasing radon concentration. When accounting for uncertainties in the retrospective exposure estimation the risk increases by about 16 % whenever concentration increases by 100 becquerels per cubic meter (Bq/m³). Accordingly, compared to a person without any radon exposure, an individual exposed to a long-term radon concentration of 100 Bq/m³ has a 16 % higher risk for lung cancer, an individual exposed to 200 Bq/m³ has a 32 % higher risk, and so on.

Even when restricting the risk analysis to participants with less than 200 Bq/m³, the linear risk model demonstrates a statistically significant risk. When considering only never-smokers, a statistically significant increase in risk of about 10 % is found.

The table below shows the probability of dying from lung cancer by age 75 years as a function of radon concentration for never-smokers and current smokers who smoke about one pack (15-24 cigarettes) per day. The following assumptions are made:

  1. The lung cancer risk of a current smoker of one pack per day is 25 times higher than that of a never-smoker.
  2. The linear risk increase is 16 percent per additional increase of 100 Bq/m³ in radon concentration, independent of smoking status.

Probability (given as death per 1.000 persons) of dying from lung cancer by age of 75 years as a function of radon concentration for smokers (one pack per day) and never smokers
Radon concentration
in Bq/m³
Deaths per 1,000 never-smokersDeaths per 1,000 current smokers
200 5.4130
4006.7 160
8009.3 216

Source: Darby et al. 2005

Number of lung cancer deaths caused by radon

The proportion of lung cancer deaths caused by indoor-radon in Europe was roughly estimated in the pooled European analysis.

According to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), the population-weighted mean of radon concentrations in dwellings in the European Union is about 59 Bq/m³. Assuming a linear increase in risk of 16 % per 100 Bq/m³, indoor radon causes nine % of all lung cancer deaths and two % of all cancer deaths in Europe. In absolute numbers, this results in about 20,000 lung cancer deaths per year in the European Union caused by radon (Darby et al. 2005).

The average indoor radon concentration in Germany is 49 Bq/m³. According to latest estimations, indoor radon causes about five % of all lung cancer deaths in Germany. In absolute numbers, this means that 1,900 lung cancer deaths per year can be attributed to radon (Menzler et al. 2006).

Smoking and radon

The radon-induced risk increase from the baseline risk is comparable for current smokers, ex-smokers and never-smokers. However, since current smokers and to some extent ex-smokers have a much higher baseline risk for lung cancer, an equally high relative risk results in a much higher absolute risk for smokers than for never-smokers. The majority of radon-induced lung cancer deaths therefore concern current and ex-smokers.

The table at "risk assessment" shows the probabilities of dying from lung cancer by age 75 as a function of radon concentrations separated for never-smokers and current smokers of one pack per day. The risk for ex-smokers who stopped smoking less than 10 years ago is approximately 80 % of the risk of a current smoker of one pack per day.

In a group of 1,000 current smokers, assuming a radon concentration of 800 Bq/m³ one can expect 216 lung cancer deaths by age 75, compared to 101 lung cancer deaths at 0 Bq/m³ (hypothetically). In 1,000 never-smokers under the same circumstances, the number of expected lung cancer deaths increases from four to nine.


WHO radon handbook

The WHO handbook on indoor radon published in 2009 provides detailed information on:

  • Risk assessment
  • Radon measurement
  • Radon remediation and prevention
  • Cost-effectiveness assessments
  • Risk communication
  • National radon programmes

EU project "Radon Prevention and Remediation (RADPAR)"

Together with nine European partners, BfS participated in the EU project "Radon Prevention and Remediation (RADPAR)" that was completed in 2012. They issued comprehensive recommendations in different areas, for example prevention measures, protocols for the measurement of indoor radon concentrations and the design of trainings for radon measurement, prevention and remediation.

On the website Radon Prevention and Remediation -RADPAR you can find the final report of the EU project and a corresponding brochure (see also Bochicchio F et al. National radon programmes and policies: The RADPAR recommendations. Rad Prot Dosimetry 2014; 160(1-3): 14-17).

Health effects

State of 2018.09.14

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