The short answer
Radon is a colourless, odourless radioactive gas produced naturally in the ground. It can enter buildings through openings in contact with the soil and build up in indoor air.
Where does radon come from?
Small amounts of uranium occur naturally in rocks and soil. Radioactive decay produces radon gas, which can move through the ground. Local geology influences how likely elevated indoor levels are, but it does not establish the level in a particular room.
How does it get into a house?
The ground is the main source. Gaps and openings around floors and services can provide entry routes. Pressure differences between inside and outside, weather and ventilation influence concentrations. Basements need particular attention because of their contact with the ground.
Can you see, smell or detect radon yourself?
Radon has no visible appearance or smell. Do not use damp, mould, headaches or the absence of symptoms to judge a property’s radon level. Use detectors intended for radon measurement and have a validated laboratory interpret the test.
What can you do about it?
Check official guidance, measure where appropriate, and get advice on reduction if the result is elevated. Suitable mitigation changes how radon-containing air enters or leaves the building. A follow-up measurement checks whether the work has been effective.
Sources & further reading
UKHSA: information about radon ↗UKHSA: measuring radon in homes ↗UKHSA: reducing radon levels and historical costs ↗Checked 13 September 2026. General property guidance; use the original source and seek professional advice for your circumstances.