Radon: The Invisible Gas in Our Homes
Radon has no colour, smell or taste, yet it is one of the leading causes of lung cancer worldwide. Here is where it comes from and what we know about it in Indian homes.
By Saurabh Dhakad, PhD scholar, Atmospheric Chemistry and Climate Change Lab, School of Environmental Sciences, Jawaharlal Nehru University · · 3 min read
On winter nights in north India we shut the doors and windows tight. It keeps out the cold, and on bad days some of the smoke too. But a closed room also holds on to whatever enters it. One of those things is a gas we cannot see, smell or taste: radon. In this post we look at where radon comes from, why it matters for our lungs, and what we know about it in Indian homes.
A gas from the ground
Uranium is present in small amounts in almost all rock and soil. As it slowly decays, one of its daughters, radium-226, gives off radon-222. Radon is a noble gas, so it hardly reacts with anything and moves freely through the pores in soil. It leaks out of the ground and into buildings through cracks in floors, gaps around pipes and joints in foundations. Some also comes out of water, for example in a shower, but the US EPA puts this at less than 5% of indoor radon in most homes.
Outdoors, radon spreads out in the open air and stays low. Indoors, with little fresh air coming in, it can build up. Ground-floor rooms and basements usually have the most.
The real problem is what radon becomes
Radon has a half-life of 3.8 days. It breaks down into a short chain of radioactive metals, the most important being polonium-218 (half-life about 3 minutes) and polonium-214 (a fraction of a millisecond). Unlike radon, these are not gases. They stick to dust and fine particles in the room. When we breathe them in, they settle on the lining of our airways and give off alpha particles right there, damaging the cells. Most of the radon gas itself we simply breathe out again.
What the numbers say
- WHO estimates that radon causes 3% to 14% of lung cancers, depending on a country's average radon level and how many people smoke.
- In many countries it is the second biggest cause of lung cancer after smoking, and the main cause among people who have never smoked.
- Lung cancer risk goes up by about 16% for every 100 Bq/m3 rise in long-term radon exposure.
- Radon in homes was linked to an estimated 84,000 lung cancer deaths worldwide in 2019.
WHO suggests a reference level of 100 Bq/m3 for homes, and not more than 300 Bq/m3 where that cannot be met. One becquerel (Bq) means one radioactive decay per second. Smoking and radon also work together: WHO notes that smokers are about 25 times more at risk of radon-induced lung cancer than non-smokers.
And in Indian homes?
Indian researchers have measured radon and its cousin thoron in many regions, often with solid-state track detectors left in rooms for weeks or months. Levels depend strongly on the local soil and building materials, and homes in the Himalaya have been surveyed closely for this reason. A 2024 study of houses in Kapurthala district, Punjab, found average radon of 27.4 Bq/m3 in winter and 15.9 Bq/m3 in summer, within safe limits. The winter value is higher because homes are closed and less ventilated, the same reason other indoor pollutants build up in the cold months.
What this means
For most homes in the plains, radon is not a cause for alarm, but it is a good reminder that indoor air has its own chemistry. Simple habits help: airing rooms when the outdoor air is cleaner, sealing large floor cracks during repairs, and keeping ground-floor and basement rooms well ventilated. More long-term measurements across India, especially in rocky and hilly areas, schools and new buildings, would show where radon really needs attention. Only a test can tell the level in a particular home.
References and further readings
- World Health Organization (2009). WHO calls for tighter standards on indoor radon. WHO news release, 21 September 2009.
- World Health Organization (2021). More countries act against exposure to radon and associated cancer risks. WHO news release, 4 February 2021.
- US EPA. Radon (Rn): radionuclide basics, and the Radon-222 decay chain.
- Estimation of indoor radon, thoron, and their progeny concentrations in different types of dwellings in the Kapurthala district of Punjab, India (2024). Radiation Protection and Environment.
- Ramola, R. C. (2011). Survey of radon and thoron in homes of Indian Himalaya. Radiation Protection Dosimetry, 146(1–3).
- Finlayson-Pitts, B. J. and Pitts, J. N. Chemistry of the Upper and Lower Atmosphere, Chapter 15 (Indoor air pollution).