What Is Radon Gas?


Definition and brief overview of radon gas

Radon is a naturally occurring element that exists mostly in a gaseous state. It is a colourless and odourless gas that cannot be detected visually.1 It was discovered by Ernest Rutherford and Robert Owens in 1899. This was followed by a discovery from Marie and Pierre Curie about Radon’s radioactive properties and how it can retain this radioactivity for a month. Radioactivity refers to an element's ability to release harmful particles or waves of energy as the element decays and breaks down. 

Significance of radon as a health concern and environmental issue

Radon is naturally occurring meaning that is always present in the environment, and its radioactive properties make it the second most common cause of lung cancer (after smoking, and the most common cause amongst non-smokers).2 

Radon's Origin and Occurrence

Explanation of radon's natural formation

Radon is formed by the decay of different radioactive metals that are present in rocks, soils and groundwater. This includes metals such as uranium and radium. As these metals decay and break down, they form radon gas which is not stuck underground as a solid metal. The process of radioactive decay is continuous and the amount of radioactive metals in a region can vary resulting in different regions having different concentrations of radon gas. 

Prevalence in the environment (soil, rocks, groundwater)

The radioactive metals that decay to form radon are solid and are present in the soil, rocks and natural sources of water underground. However, naturally occurring radon takes on a gaseous state meaning that it can travel up to the surface as gases are free to move. This means that radon gas can be found nearly everywhere on Earth, though there are areas which are associated with a much higher concentration of radon gas. In most other regions it can be considered a source of background radiation and is at a much lower concentration that is not considered to be immediately harmful. Nevertheless, a build-up of radon gas can still be a health risk even in areas where it is not present in very high concentrations.

Radon and water

As radon is present underground, it can find its way into water sources such as natural springs and contaminate sources of drinking water. Radon dissolves easily in water allowing it to be transported to long distances through natural water sources.3 While inhaled radon gas is more of a health risk than ingested radon, it can still cause health problems. This is more of an issue with homes that have their private water source or with wells rather than with reservoirs as their radon levels are closely monitored. 

Health Risks Associated with Radon

Radon gas is one of the leading causes of lung cancer. When inhaled, the radon gas will continue to decay and release alpha particles as it breaks down. The alpha particles can be absorbed by the lung tissue which results in damage to the tissue in the lungs.4 Over time this damage can cause lung cancer. But it can also cause other health problems especially if you already suffer from respiratory issues (due to the damage to the lung tissue by the alpha particles). 

Pathways of Radon Entry

How radon enters homes and buildings (soil, foundation cracks)?

As Radon gas is formed underground, it rises to the surface and can enter homes and other buildings through cracks in the foundation of the building as it leaves the soil). It can also enter through any other openings in the building’s structure. Radon gas is also likely to enter subterranean levels like basements as they are below ground level and rise through the building. 

Factors influencing indoor radon levels

There are many factors that can influence indoor radon levels such as geographical location. Radon is naturally occurring and can be found in higher concentrations in some regions while it may be in very low concentrations in other areas. Areas with low radon gas concentrations will naturally have lower radon gas levels in buildings compared to regions with high concentrations (when comparing structurally identical buildings). Additionally, the construction of the building can also have an impact on radon gas levels- poorly constructed buildings with weak foundations are more likely to allow the gas to rise through the structure from the soil. Furthermore, ventilation systems can be used to reduce the radon levels in a building therefore a building without an adequate ventilation system will have a higher radon concentration inside. If you live or work in an area that is known to have a high radon concentration, it would be advised for you to have a ventilation system installed. 

Measuring Radon Levels

Radon testing methods

Radon levels can be tested with detectors- small devices placed inside a home or workplace which monitor the radon amount over time. Normally, the radon levels are monitored for three months to take into account normal variations in the concentration caused by external conditions such as weather. These would need to be placed inside a room but not too high (such as on top of wardrobes or high cupboards) and also not on top of any electrical devices such as televisions or computers. 

Radon measurement units

There are two common units used in the measurement of radon gas concentration; they are Becquerels per cubic metre (Bq/m3) and picocuries per litre (pCi/L). Both units are named after the scientist associated with them.

Radon Mitigation and Reduction

Different techniques can be used to reduce the amount of radon gas present in a house or building. This can include techniques such as sealing cracks and openings to prevent radon gas from entering the building in the first place. It can also include installing or replacing a ventilation system to allow the naturally occurring radon gas to be removed from a building on its own. Another technique that can be used is sub-slab depressurisation. It is important to note that some of these techniques can be quite expensive and may not be effective if not done correctly (or even make the problem worse). Hence, it is best to consult a professional and to have any work carried out by a qualified individual. 

Radon Awareness and Regulation

The government regulations regarding radon gas differ by region. In some areas, there are strict rules regarding selling homes in regions with a high radon concentration including mitigating the risk of radon levels in a building before it can be sold. There are also rules in place for employers to make the workspace safer for their employees if they work in a high-risk area. 

Geographic Variations

The concentration of radon in an area greatly depends on the presence of radioactive metals in an area as it is the decay of these metals that produces radon gas. Many local authorities or governments carry out geological surveys and have created maps to monitor the radon concentrations in different regions. This can be helpful to learn about the radon levels in your local area. 

Homebuyer and Seller Responsibilities

Radon testing is an important responsibility of the seller before the home can be sold. The homebuyer should be fully informed about the potential risks associated with living in an area with high radon concentrations and whether there are reduction strategies put into place for their potential new home. The laws regarding the seller’s responsibilities differ by country so confirm with the real estate company or government website what checks are your responsibility when selling your home. 

Radon and Indoor Air Quality

Over time, radon gas can build up indoors and reach a dangerous concentration, particularly in areas which are poorly ventilated, and the gas cannot escape. This high level of radon gas can lead to lung cancer amongst other health problems. Additionally, poorly ventilated buildings may also have other problems that can contribute to indoor air pollution. Poor ventilation can lead to high levels of dust which may trigger allergies or asthma (and other respiratory illnesses) in some individuals. 

Protecting Yourself and Your Family

There are a lot of things you can do to protect yourself and your family. You can periodically test your house to monitor the radon levels. This way you can notice if the radon concentration is starting to increase and approach a dangerous level. This would also allow you to take early measures with reduction strategies to make your house safer. You can also have a professional come and have a look at your house and evaluate what preventative measures would be recommended for that particular structure. The first step you could take would be to seal off any cracks and openings. 


Radon is an odourless, colourless, radioactive gas that is naturally occurring and can build up in buildings. The levels of radon present in an area depend on the amount of radioactive metals found underground in a region as it is the decay (breakdown) of these metals that releases radon gas. High levels of radon gas are known to cause lung cancer and exposure to radon gas is the second most common cause of lung cancer after smoking. Fortunately, there are several ways to reduce the risk of radon gas in your home or workplace. Legislation around radon gas levels differs by region so consult your local authority on what is considered a harmful concentration for where you live.


  1. IAEA. Protection against exposure due to radon indoors and gamma radiation from construction materials - methods of prevention and mitigation. Vienna: IAEA; 2021. 1 p. (IAEA TECDOC Series). Available from: https://www.iaea.org/publications/14817/protection-against-exposure-due-to-radon-indoors-and-gamma-radiation-from-construction-materials-methods-of-prevention-and-mitigation
  2. Vogeltanz-Holm N, Schwartz GG. Radon and lung cancer: What does the public really know? Journal of Environmental Radioactivity [Internet]. 2018 Dec [cited 2023 Oct 26];192:26–31. Available from: https://linkinghub.elsevier.com/retrieve/pii/S0265931X18300171
  3. World Health Organization. Management of radioactivity in drinking-water [Internet]. Geneva: World Health Organization; 2018 [cited 2023 Oct 26]. 104 p. Available from: https://iris.who.int/handle/10665/272995
  4. Riudavets M, Garcia De Herreros M, Besse B, Mezquita L. Radon and lung cancer: current trends and future perspectives. Cancers [Internet]. 2022 Jun 27 [cited 2023 Oct 26];14(13):3142. Available from: https://www.mdpi.com/2072-6694/14/13/3142
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Saba Amber

Medicinal and Biological Chemistry- BSc, Manchester Metropolitan University

Saba is a recent graduate in Medicinal Biochemistry with a particular interest in pharmacology.

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