The short answer
Long-term exposure to radon increases the risk of lung cancer. The practical response is to measure exposure and reduce elevated indoor levels, rather than look for immediate symptoms.
Why long-term exposure matters
Radioactive decay products from radon can be inhaled and damage lung tissue. Risk is related to the concentration and duration of exposure. A test result is a property exposure measurement, not a medical diagnosis.
Smoking changes the risk
Smoking and radon together create a greater lung cancer risk. UKHSA specifically advises considering reduction between the Target and Action Levels where a smoker or ex-smoker lives. For personal health concerns or help to stop smoking, contact a healthcare professional.
Understand the domestic reference levels
The UK domestic Action Level is 200 Bq/m³ and the Target Level is 100 Bq/m³. These are based on an annual average. They are not a line separating all risk from no risk, and short-term spikes need careful interpretation.
A practical response
Keep your focus on a reliable measurement, the laboratory’s interpretation and appropriate reduction where advised. Speak to a specialist if results are very high, or contact UKHSA for guidance. Do not wait for symptoms to investigate an elevated test result.
Sources & further reading
UKHSA: information about radon ↗UKHSA: Action Level and Target Level ↗UKHSA: measuring radon in homes ↗Checked 13 September 2026. General property guidance; use the original source and seek professional advice for your circumstances.