Radon and smoking: why the combination multiplies lung cancer risk

Radon and tobacco smoke are the two leading causes of lung cancer in the United States. Each is dangerous on its own. Together, they're far worse than either one alone. If anyone in your home smokes, or used to, radon testing deserves a place near the top of your to-do list. This guide explains EPA's numbers and what they mean in practice.

The headline numbers

According to EPA:

• Radon is the second leading cause of lung cancer overall, and the number one cause among people who have never smoked.
• Radon is responsible for about 21,000 lung cancer deaths in the U.S. every year.
• About 2,900 of those deaths occur among people who have never smoked. That means the large majority occur among current and former smokers.
• Secondhand smoke is the third leading cause of lung cancer, responsible for an estimated 3,000 lung cancer deaths a year.
• EPA says smokers are at higher risk of developing radon-induced lung cancer.

Comparing risk at the same radon level

EPA's risk tables estimate how many people out of 1,000 could get lung cancer from a lifetime of exposure at different radon levels:

Radon level	Never smoked	Smokers
20 pCi/L	about 36	about 260
10 pCi/L	about 18	about 150
8 pCi/L	about 15	about 120
4 pCi/L	about 7	about 62
2 pCi/L	about 4	about 32
1.3 pCi/L (average indoor level)	about 2	about 20

At every level, the risk for smokers is roughly seven to nine times the risk for people who have never smoked. At EPA's action level of 4 pCi/L, it's about 62 per 1,000 for smokers compared with about 7 per 1,000 for never-smokers.

Why the combination is so harmful

Scientists explain the interaction this way. Radon's radioactive decay products attach to tiny particles in the air and can lodge in the airways, where they release radiation that damages cells. Tobacco smoke independently damages the same lung tissue and may also affect how particles deposit and clear from the lungs. Two sources of damage acting on the same cells combine to raise cancer risk more than either alone would.

What it means for different people

Current smokers. Your radon risk is much higher than a non-smoker's at the same level. Quitting is the most effective single step you can take, and testing and fixing your home lowers your remaining risk further.

Former smokers. Your risk from past smoking declines over time after quitting, but you still benefit from keeping radon exposure low. Testing is especially worthwhile.

Never-smokers living with smokers. You face secondhand smoke and radon. Keeping your home smoke-free and testing for radon both reduce your risk.

Households with children. EPA says there's no evidence children are at greater risk of radon-induced lung cancer than adults. But children are exposed to secondhand smoke and radon over many years at home, so reducing both gives them a healthier start.

The two most effective steps

1. Stop smoking, and keep the home smoke-free. The CDC says there are proven treatments, and that using counseling and medication together gives people the best chance of quitting for good. Free coaching is available through the quitline at 1-800-QUIT-NOW (1-800-784-8669), and nicotine replacement (patch, gum, lozenge) is sold over the counter. The CDC also notes that more than half of U.S. adults who smoked have quit.
2. Test for radon, and fix high levels. EPA recommends fixing homes at or above 4 pCi/L and considering a fix between 2 and 4 pCi/L. EPA says some radon reduction systems can reduce levels by up to 99 percent.

Doing both gives the biggest reduction in lung cancer risk.

Talking with your doctor

If you smoke or used to, and you've lived in a home with high radon, tell your doctor. They can talk with you about your overall lung cancer risk and whether lung cancer screening is appropriate for you under current medical guidelines. Screening recommendations are based mainly on age and smoking history, but your doctor may want to know about radon exposure too.

Myths to drop

• "Radon only matters if you smoke." No. It's the leading cause of lung cancer among non-smokers.
• "If I smoke, radon doesn't matter, because I'm already at risk." The opposite is true. Smoking makes radon more dangerous.
• "Air purifiers fix radon." Typical home air purifiers aren't a substitute for radon mitigation. The proven approach is to stop radon from entering, usually with a sub-slab or submembrane suction system.

A household action plan

• This week: order a radon test kit, or ask your state radon program about free or low-cost kits.
• Test in the lowest lived-in level, following closed-house conditions.
• If the result is 4 pCi/L or higher: confirm it, then get estimates from qualified mitigators.
• At the same time: set a quit date, call the quitline, and talk to a health care provider about medication options.
• Make the home smoke-free, inside and in the car.
• Retest after mitigation, and at least every two years after that.

Secondhand smoke and visitors

Making your home smoke-free protects everyone in it, including guests and children. If someone in the household isn't ready to quit, smoking outside and away from doors and windows reduces secondhand smoke indoors, though it doesn't remove the smoker's own combined risk from radon.

Where to start

Order a short-term test kit, follow the instructions carefully, and test in the lowest lived-in level of your home. See how to test your home for radon. If anyone in your household smokes, consider that one more reason to test this month rather than someday.

Key takeaways

• In EPA's tables, smokers face roughly seven to nine times the radon-related lung cancer risk of never-smokers at the same level.
• Quitting and fixing radon together give the biggest risk reduction.
• Free quit help: 1-800-QUIT-NOW.