Radon health risks: what the evidence says

Radon is not an abstract risk. It is one of the best-studied environmental causes of cancer, and the evidence comes from both underground miners and people exposed in their own homes.

The main numbers

EPA estimates that radon causes about 21,000 lung cancer deaths in the United States each year, and that about 2,900 of those deaths occur among people who have never smoked. That makes radon, by EPA’s estimate, the second leading cause of lung cancer overall and the leading cause among nonsmokers. These are modeled estimates based on large studies, not a count of death certificates, and EPA presents them that way.

The only known health effect is lung cancer

EPA says the primary health risk from radon is lung cancer. Radon decay products are inhaled, deposit in the airways, and emit alpha radiation that can damage the cells lining the lungs. Radon is not known to cause other symptoms such as headaches or coughing, and there are no short-term warning signs. Harm builds up over many years of exposure.

Smoking multiplies the risk

Radon and smoking act together. EPA notes that a smoker who is also exposed to radon has a much higher risk of lung cancer than would be expected from either alone. If you smoke and live with elevated radon, reducing both has the largest effect. For people who have never smoked, radon is the most important preventable lung cancer risk EPA identifies.

How scientists know

EPA points to three lines of evidence:

• Miner studies. Underground uranium and other miners exposed to high radon levels had clearly higher lung cancer rates, and risk rose with exposure.
• Residential studies. Pooled analyses of studies in North America, Europe, and China found increased lung cancer risk from radon in homes, at levels found in ordinary houses.
• Scientific reviews. The National Academy of Sciences’ BEIR VI report (1999) and the World Health Organization’s 2009 Handbook on Indoor Radon both concluded that residential radon causes lung cancer.

Is there a safe level?

EPA says any radon exposure carries some risk, and the risk rises with the level and the length of exposure. EPA’s action level of 4 pCi/L is where it recommends fixing a home; it recommends considering a fix between 2 and 4 pCi/L. The WHO proposed a reference level of 100 Bq/m³ (about 2.7 pCi/L). Use our level calculator to see where your result falls.

What reduces the risk

Fixing a home works. EPA says radon reduction systems can lower levels by up to 99 percent in some homes. Testing costs little, and the fix is usually a one-time installation. See radon mitigation systems.

Talk to a doctor if you are worried

If you have lived for years in a home with high radon, especially if you smoke or used to, talk to your doctor about your lung health and whether screening is appropriate for you. This site cannot give medical advice.