When most people hear lung cancer, they think cigarettes. But that can be a mistake. While cigarette smoking is hands down the number-one risk factor for lung cancer, radon is a very real danger that doesn’t get the attention it deserves. 

Radon is the leading cause of lung cancer in nonsmokers—and accounts for about 21,000 deaths from the disease each year, according to the Environmental Protection Agency (EPA). Many of these deaths occur in people who never smoked. If you do smoke—and your home has high radon levels—this one-two punch makes your risk for lung cancer especially high. Facts to know about this silent killer…

A Widespread Indoor Threat

Radon occurs naturally when uranium, an element found in rocks and soil, decays. As the element breaks down, it releases radon gas. Even though radon can be found outdoors in harmless amounts, it can accumulate in homes and buildings that are constructed on soil with natural uranium deposits, as the air is trapped inside the building.

Radon is an insidious threat because it cannot be seen, tasted or smelled. When radon is inhaled, it causes no symptoms even though invisible particles are attacking the body’s cells with cancer-causing radiation. 

Thousands of lung cancer deaths would be avoided each year if home and building owners tested and fixed high levels of radon, according to the American Lung Association. 

So why are there still so many deaths linked to radon? Over the years, several myths have emerged, undermining efforts to eradicate this pervasive health threat. For example…

Don’t Be Fooled by These Myths

Myth #1: Radon is a concern only in certain parts of the country. Fact: It’s true that radon exists in higher concentrations near uranium-dense rock deposits, but radon can be found everywhere. In total, nearly one in every 15 homes in the US is estimated to have radon levels that exceed the EPA’s recommendation. The EPA has mapped the country into three zones. While the highest levels are generally found in northern states, moderate-­risk counties exist in every state except Louisiana. And even in low-risk areas, a single neighborhood might be sitting on a pocket of uranium. For a US map that indicates average radon levels by state and zone, check the EPA Map of Radon Zones (at EPA.gov/radon, search “map of radon zones”).

Myth #2: I’ve lived in my home for decades, so there’s no point in testing now. Fact: Regardless of whether your home was tested for radon when you purchased it, testing should be repeated every five to 10 years. Radon levels can change over the years as your home settles, the ground shifts and new cracks form. And if a test you conduct now indicates that radon levels in your home are high, that doesn’t necessarily mean you’ve had long-term exposure. But because the harmful effects of radon are cumulative, the sooner you address the problem, the lower your risk. 

Myth #3: I have a brand-new home, so there’s nothing to worry about. Fact: Some states do require new homes to be radon-resistant, but most don’t. Because new homes are built to be more energy-efficient, they’re more efficiently sealed. That means new homes can trap whatever radon might emerge from the soil under the house—so they may become even more prone to higher radon levels than older homes.

Myth #4: Testing is too expensive and time-consuming. Fact: You can buy a basic home test for under $15 at many hardware stores, and some states even provide them for free. 

With most tests, you set it up, leave it in place for a minimum of 48 hours and then mail it to a lab for evaluation. Long-term tests may remain in a home for 90 days or more—these tests are used when home owners want a more stable, average level.

Myth #5: If I test my home and the levels are too high, I won’t be able to sell it later on. Fact: Radon testing is a routine part of home inspections in many states, so if you have a problem, it could hold things up when you do decide to sell your home. Plus, remediation may be easier than you think. If you have obvious cracks in your basement floor, for example, DIY sealing can be easy and inexpensive—hardware stores sell products made for this purpose. Just retest after performing this type of sealing to ensure that radon levels were adequately reduced. 

If the levels are still dangerously high, you may need a remediation system that uses a vent pipe and fan to pull radon to the outside. Such systems cost about $800 to $2,000, depending on your home and location.