Radon, the little-known health hazard hidden in many Spanish homes that causes cancer.

Around 1,500 people a year die in Spain due to a little-known public health problem: the presence of the radioactive gas radon in homes. This phenomenon, in fact, is the second most common cause of lung cancer in our country , after tobacco.

What is radon and why is it harmful?

Radon is a colorless, odorless, and tasteless radioactive gas (and therefore impossible to detect without special devices) that occurs naturally from the decay of uranium present in soil and rocks. As the World Health Organization indicates, radon dissolves quickly outdoors and is not usually dangerous, but it can penetrate cracks in buildings and accumulate in closed spaces, especially if they are poorly ventilated.

Because its presence depends largely on the geology of each area, the risk it represents is not the same throughout Spain. Specifically, the areas of our country where mortality from this cause tends to be highest are the northwest of the peninsula (particularly Galicia) and areas in the center-west and west (such as Extremadura), according to the Ministry of Health report . It is also present in some mountainous areas, including the Pyrenees and the Central System.

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Radon, when inhaled, increases the risk of certain types of cancer (primarily lung cancer; in fact, it is the leading cause of this cancer in nonsmokers). Therefore, it is considered by the WHO to be a category 1 human carcinogen, the same as alcohol, tobacco, asbestos, and arsenic.

What is the magnitude of the risk in Spain?

Although there is no known threshold dose below which there is no risk to human health, we do know that the risk of lung cancer from exposure to radon increases linearly and statistically significantly by 16% for every 100 becquerels per cubic metre (Bq/m³), according to the reference study on the subject published in 2005 in the prestigious academic journal BMJ .

To give an idea, according to data from the Spanish Nuclear Safety Council (CSN), the radon potential (calculated based on the 90th percentile of the distribution of radon levels in buildings in a given area) exceeds 400 Bq/m3 in areas of Galicia, Catalonia (including the Barcelona area), Castilla y León (western area and Central system), the Community of Madrid (mainly in mountain areas), much of Extremadura, in the Sierra Nevada area and in a good part of Tenerife and Gran Canaria.

According to WHO recommendations, radon levels in buildings should be reduced to below 100 Bq/m³; and, in any case, human exposure should not exceed 300 Bq/m³.

How to protect ourselves from radon

Beyond public health policies aimed at measuring and reducing radon levels, there are some individual precautions that can help us reduce our risk of developing lung cancer from this cause.

For example, it's possible to install radon measurement and mitigation systems in homes. Also, as the U.S. Centers for Disease Control and Prevention (CDC) reminds us, we can try to seal cracks in floors and walls, which are the common entry point for this gas into homes. Radon-resistant construction techniques are increasingly being used in new construction homes.

Finally, and although it only works temporarily , it is important to try to maintain adequate ventilation in the rooms of the house, which greatly helps to reduce the specific levels of radon in that space.

References

WHO (2021). Radon and its health effects. Accessed online at https://www.who.int/news-room/fact-sheets/detail/radon-and-health on June 30, 2025.

Ministry of Health (2021). Mortality attributable to residential radon exposure in Spain. Accessed online at https://www.sanidad.gob.es/ciudadanos/saludAmbLaboral/docs/04_Mortalidad_radon.pdf on June 30, 2025.

S Darby, D Hill, A Auvinen, JM Barros-Dios, H Baysson, F Bochicchio, H Deo, R Falk, F Forastiere, M Hakama, I Heid, L Kreienbrock, M Kreuzer, F Lagarde, I Mäkeläinen, C Muirhead, W Oberaigner, G Pershagen, A Ruano-Ravina, E Ruosteenoja, A Schaffrath Rosario, M Tirmarche, L TomáBek,

E Whitley, HE Wichmann, R Doll. Radon in homes and risk of lung cancer: collaborative analysis of individual data from 13 European case-control studies. BMJ (2005). DOI: https://doi.org/10.1136/bmj.38308.477650.63

CSN (2017). Map of radon potential in Spain. Accessed online at https://www.csn.es/mapa-del-potencial-de-radon-en-espana on June 30, 2025.

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