What is radon?

The great Radon Guide

What is radon?

Many people have no idea of the danger taking place in their homes. Radon accumulates in their buildings in cellars and threatens the health of adults and children. Radon is the second most common cause of lung cancer in Germany. Only smoking is more dangerous. According to the Federal Office for Radiation Protection (BfS), 5-10% of all cases of lung cancer are caused by invisible gas. [1]

Radon is a radioactive gas that emits alpha radiation on decay. The gas is present in the soil - but it is also contained in many building materials. The human senses do not perceive radon because it is tasteless, colourless and odourless. Of all natural radiation sources, radon makes the largest contribution to radiation exposure in Germany.[2]

Normally the exposure to radon in the fresh air is low. The values are in the range of 2-40 Becquerel per cubic meter of air (Bq/m3). However, the gas can accumulate in buildings, resulting in harmful radon concentrations. In severe cases, the values in cellars and living rooms are 1,000-10,000 Bq/m3 – or higher. Now, at the latest, remediation measures are necessary in order not to endanger health unnecessarily.


- Radon is radioactive. It occurs almost everywhere in buildings

- Radon is the second most common cause of lung cancer after smoking

- There's no visible sign of radon.

- Extensive ventilation as an important measure in the fight against radon

How does radon come from?

Radon is formed wherever uranium or thorium are present in the soil. The decay of these elements releases radon-222 (Rn-222) with a half-life of 3.8 days. The formation of radon-222 also produces other radon isotopes (e.g. Rn-220 or Rn-219). However, their half-life is so short that they pose no danger to humans. Radon-222 is different: With a half-life of 3.8 days, radon-222 has enough time to reach the earth's surface and accumulate in rooms such as cellars or rooms on the ground floor. The decay of radon-222 releases alpha radiation. The products of radon-222 are also radioactive and also (predominantly) decay by alpha radiation.

Am I affected by radon?

Pretty sure: yes. Because every one of us spends his or her life in places polluted by radon. Whether at work, at school or at home, there is hardly anyone who has not been exposed to high levels of radon before.

In addition to the radon concentration, the duration during which humans are exposed to the radioactive gas and its derivatives is decisive for a health hazard. Inhaling radon at high concentrations over a long period of time significantly increases the risk of developing lung cancer.

How does radon get into my house?

Radon is formed in the ground and rises there until it reaches the surface. It dilutes quickly in the fresh air. If, however, the gas hits buildings, it enters through cracks, joints and cracks and can accumulate in the lower rooms (basement, ground floor). The radon reaches the upper floors through suction effects (open windows, heated rooms).

Radon cannot only enter the house through leaks, however. Further possibilities are:

- Drinking water: The water-soluble radon is also contained in drinking water. When taking a shower, for example, radon can gas out. The increased radioactivity is often clearly measurable after showering.

- Building materials: Some building materials contain large amounts of radioactive isotopes. Radon-222 is produced by the decay of radium-226.

Both building materials and drinking water can significantly increase the radon load in a building. As a rule, however, radon enters the interior of a building via the ground.

Which regions are particularly affected by radon?

The extent to which a region is contaminated with radon depends on the soil composition and the uranium content of the soil. As the soils in southern Germany are particularly rich in uranium, high radon concentrations can be measured there. Radon risk areas are currently known: The Black Forest region, the Erzgebirge, large parts of Thuringia and the Fichtelgebirge. Radon is also increasingly found in the Bavarian Forest and in the Alpine region. But not only the south and the east of Germany are highly polluted: there are also hotspots in northern Germany, such as the eastern coastal region of Schleswig-Holstein or the plöner hinterland.

In addition to the uranium content of the soil, the soil composition also plays a role in the level of radon concentration. Fissured soils with deep cracks and crevices, mining regions or sandy and gas-permeable soils favour the formation of high radon concentrations in buildings and near-ground air.

Radon maps published by the Federal Office for Radiation Protection (BfS) provide a rough overview of radon contamination in soil air. The Federal Office for Radiation Protection has carried out investigations at several thousand measuring sites. However, the maps only provide a rough overview of radon exposure in a region. Radon values can vary from house to house, which is why radon measurements should always be determined individually.

How can I measure radon?

Different measuring methods are available for each test medium (room air, soil air, water). For the measurement of radon, active and passive measuring systems are available on the market.

Active measuring instruments measure electronically and have a display on which the values are shown. Most active instruments are used for short-term measurements. Passive measuring devices register the decay on a plastic film, which is evaluated in a special laboratory after the measurement. Passive measuring systems are particularly suitable for long-term measurements. In addition, there are measuring instruments that detect radon directly in the air, while others detect the decay products of radon.

Radon measurements can also be carried out in private households. For example, devices such as the "Radon Eye from FTLAB" or the "Corentium Home from Airthings" are suitable for measurements in private homes. If you have some time, you can also achieve good results with passive dosimeters. It is important that the time period for the measurement is chosen long enough.

Radon values vary depending on the time of year or day. In order to obtain meaningful readings, radon measurements with active measuring devices should last at least 4-10 days, with passive measuring devices at least 1-12 months.

Why do radon values fluctuate?

Radon measurements should be carried out in the long term, as radon concentrations often fluctuate. The measurement is subject to daily and seasonal fluctuations. What counts in a radon measurement, however, is the long-term mean value. Short measurements are extrapolated to an annual average value.

Time-of-day fluctuations in measurement in buildings are caused by changes in temperature, wind conditions and air pressure. In addition, lifestyle also plays a role in radon concentration. Do you ventilate frequently or does the basement have no windows? Do you open doors often or less often? All this affects the average exposure to radon. Overnight, the levels often rise. During the day, the values decrease due to increased activity (opening and closing doors) and increased air exchange (ventilation, opening and closing front doors, etc.) in the building.

Seasonal fluctuations occur due to changes in the soil structure during ground frost. The gas finds other ways in frozen soils and thus frequently enters the interior of buildings. At the same time, there is less ventilation in winter than in summer. As a result of the suction effect created in the building during heating (rising air), radon is increasingly sucked into the building from the ground, which is why the radon concentration increases. The rising air also ensures that radon reaches the upper floors.

How dangerous is radon for my health?

According to the Federal Office for Radiation Protection, a sustained increase in the radon concentration in indoor air of 100 Bq/m3 leads to a 16 % increase in the risk of lung cancer. [3] In Germany about 1900 deaths per year can be attributed to radon gas. EU-wide, the authorities expect 20,000 deaths per year.[4]

Radon itself is not toxic. Inhaling radon does not cause symptoms such as headaches or dizziness. It is the radioactivity that makes the gas so dangerous. The decay of radon releases alpha radiation, which damages the human body. In addition, its decay produces secondary products (e.g. radioactive lead, bismuth and polonium), which in turn are predominantly alpha emitters. When inhaled, the radioactive derivatives together with aerosols (radioactive derivatives adhere to dust water droplets) enter the lungs where they damage lung tissue.

In order to minimise the risk of lung cancer, it is recommended that radon levels be minimised. In kindergartens and schools, the annual average values should not exceed 100 Bq/m3. From January 2019, employers will be required to reduce workplace radon levels below 300 3 on an annual average.

Can radon also cause skin cancer?

A Swiss study suggests that radon, in addition to UV radiation, increases the risk of skin cancer. According to this study, alpha radiation, which is produced when radon-222 decays, has a similar skin-damaging effect to UV radiation. The study also showed that young people are more affected by this effect than older people.[5]

Are smokers particularly endangered by radon?

Studies indicate that radon and tobacco consumption are mutually reinforcing in their harmful effects. Smokers are therefore exposed to a significantly increased risk of cancer, even if the radon load is high. [6] The following table illustrates the relationship between tobacco consumption and radon exposure.

Table: Risk of dying from lung cancer up to the age of 75 years [7]

Radon concentration

0 Bq/m3

Radon concentration

800 Bq/m3

Lifelong non-smokers

0,4 %

0,7 %

Smoker*) until the age of 30

2,3 %

3,7 %

Smoker*) up to 50 years of age

4,3 %

7,2 %

Smoker*) up to 75. years of age

10,4 %

16,9 %

*) for 15-24 cigarettes daily

How dangerous is radon for my children?

In general, radioactivity is more dangerous for children than for adults. Their tissue is particularly sensitive to ionising radiation. This is why children, for example, are x-rayed as rarely as possible.[8]

Cancers are often the result of a triggering event (e.g. increased radiation). However, it sometimes takes decades for cancer to break out. When elderly people are exposed to increased radiation, they often no longer experience the outbreak of cancer. In younger people, the body has more time to develop tumours during their lifetime. In addition, the body of a child is generally more sensitive to radiation because the cells of the child's body divide more often. Cell division is an important prerequisite for cancer to develop at all.

In terms of radon, this means that children should not be exposed to increased levels of radon. It is therefore important that children's homes are tested for radon. In addition, schools and kindergartens should pay attention to thorough radon testing.

Which buildings are particularly affected by radon?

It is difficult to predict which types of buildings are increasingly affected by radon. Radon is found practically everywhere and can be found in new buildings as well as in old buildings, schools and kindergartens. However, buildings with cracks in the building envelope or a leaking floor slab are generally particularly unsafe as far as radon entry is concerned. If you find a natural floor in your cellar or the cellar is made of natural stone, then a radon measurement certainly makes sense. Even if you live in a radon risk area, you should not delay a radon measurement for too long. Since radon values also vary greatly within a region and often differ significantly from house to house, room air analyses are recommended for all people in Germany.

Why does radon accumulate in cellars?

In many houses there is always a slight negative pressure, because warm, heated air rises upwards and creates a slight suction. The negative pressure draws radon from the ground into the building. This affects all areas that come into contact with the ground, such as the cellar or the ground floor. The radioactive gas enters the lower rooms of a building through existing cracks and leaks such as pipe and line penetrations. Since radon is heavier than air, it accumulates in the lower rooms. In addition to the amount of gas that enters the house through the leaking building envelope, the amount of gas that escapes from the building materials must also be added. Radon is also almost always dissolved in tap water, which can then e.g. gas out when showering.

The radon, which once arrived in the cellar, can also ascend to the upper floors. The gas can also reach the upper floors as a result of suction effects such as those caused by heating or ventilation. Air currents and thermal mixing mechanisms draw the radioactive gas upwards, especially if cellar doors are not closed or leaky.

What can I do against radon?

First of all you should carry out a radon measurement. With modern, electronic measuring devices this should not be a problem. Already after a few days you will get an overview of the radon situation in your house. You can either buy or rent the radon meters. For a rental device you pay about 40-50 Euro for three weeks. This is enough to intensively test 2-3 rooms for radon. If you would like to own a radon measuring device, then you are there with approx. 180-280 Euros - depending on the equipment and functional scope.

You've detected elevated radon levels? Then you can reduce the radon concentration with some immediate measures: Open windows and doors and ensure a draught in your house. With modern measuring instruments you can observe how the radon concentration drops immediately. Provide plenty of fresh air in your house on a regular basis! If the radon levels remain high, then renovation measures may be necessary.

When do radon remediation measures become necessary?

If simple ventilation is no longer sufficient, renovation measures are necessary. Various techniques are used for renovation measures:

- Installation of ventilation systems

- Sealing of cracks and cracks in the cellar

- Sealing of all radon entry points such as pipe and cable bushings

- Sealing of cellar doors and windows

- Installation of a radon well

What are the limits for radon?

At the moment there is no limit value (as of September 2018), but only a reference value for radon, which is 300 Bq/m3 on an annual average. However, the Federal Office for Radiation Protection has been demanding a limit value of 100 Bq/m3 as an increased risk of lung cancer already exists from this value.

German authorities are in the process of establishing radiation protection areas. As of January 2019, many employers will be obliged to measure in the workplace. However, only employers within radon risk areas will be affected. If the annual average limit value of 300 Bq/m3 is exceeded, the employer must initiate countermeasures. These can be special ventilation measures, but also renovation measures. The new law only affects employers. There will be no changes for private tenants and landlords. For them only the recommendation of the Federal Office for radiation protection (BfS) applies to keep the radon value below 100 Bq/m3 in the annual average.


[5] https://ehp.niehs.nih.gov/doi/10.1289/ehp825

[8] https://www.focus.de/panorama/welt/tsunami-in-japan/wissenschaftliche-hintergruende/radioaktivitaet-die-kleinen-mit-dem-groessten-risiko_aid_609553.html

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