Evidence reviewed by the World Health Organization (WHO) confirms that exposure to radon causes lung cancer. The risk arises from inhalation of radioactive decay products that damage lung tissue over time.

WHO estimates that radon is responsible for 3–14% of lung cancers worldwide, depending on national radon levels and smoking prevalence. Radon is identified as the second leading cause of lung cancer globally, and the leading cause among people who have never smoked. The health risk is substantially higher when radon exposure occurs alongside tobacco smoking.

WHO reports that lung cancer risk increases linearly with radon concentration, with no evidence of a threshold below which exposure poses zero risk. To reduce population health risk, WHO recommends a reference level of 100 Bq/m³ where achievable, and states that indoor radon concentrations should not exceed 300 Bq/m³.
 
This evidence establishes radon reduction as a preventable public health intervention critical to long-term disease prevention in residential environments.