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.

EPA's risk tables, in plain numbers

EPA publishes estimates of how many people out of 1,000 could get lung cancer if exposed to a given radon level over a lifetime.

If you have never smoked:

Radon level	About how many of 1,000 could get lung cancer	EPA recommendation
20 pCi/L	36	Fix your home
10 pCi/L	18	Fix your home
8 pCi/L	15	Fix your home
4 pCi/L	7	Fix your home
2 pCi/L	4	Consider fixing between 2 and 4 pCi/L
1.3 pCi/L (average indoor)	2	Reducing below 2 pCi/L is difficult

If you smoke:

Radon level	About how many of 1,000 could get lung cancer
20 pCi/L	260
10 pCi/L	150
8 pCi/L	120
4 pCi/L	62
2 pCi/L	32
1.3 pCi/L	20

The tables show two things clearly. Risk rises with the radon level, and smoking multiplies that risk many times over.

How radon damages the lungs

Radon itself is a gas that you breathe in and out. The harm comes mostly from its short-lived decay products, radioactive particles that can lodge in the lining of the lungs. As they decay, they release small bursts of radiation that can damage lung cells. Over years, that damage can lead to cancer. EPA notes lung cancer typically appears 5 to 25 years after exposure.

Who is more vulnerable?

• Smokers and former smokers, because of the combined effect.
• People who spend a lot of time at home, especially in lower levels, such as older adults, remote workers, and people with limited mobility.
• People in homes with high levels, regardless of other factors.

EPA states there is no evidence that children are at greater risk of radon-induced lung cancer than adults, and no evidence that radon causes other respiratory diseases such as asthma.

Radon and secondhand smoke

EPA calls radon the second leading cause of lung cancer overall and the leading cause among non-smokers. It lists secondhand smoke as the third leading cause, responsible for an estimated 3,000 lung cancer deaths a year. In a home with both radon and indoor smoking, reducing either lowers risk, and reducing both does the most.

What to tell your doctor

If you've lived for years in a home with high radon, especially if you smoke or used to, tell your doctor. They can discuss your overall lung cancer risk and whether screening is appropriate for you based on current medical guidelines. Testing and fixing your home lowers your future exposure, whatever your past exposure was.

The bottom line

The risk from radon is real, but it's also one of the most preventable. Test your home, fix levels at or above 4 pCi/L, consider fixing between 2 and 4 pCi/L, and if you smoke, quitting is the single biggest step you can take.