What Is Radon and Why Is It Dangerous?

What Is Radon?

Radon is a naturally occurring radioactive gas produced by the decay of uranium found in soil, rock, and water. It is colorless, odorless, and tasteless — completely undetectable by human senses. Because radon is a gas, it can seep up through the ground and accumulate inside buildings, particularly in basements and lower floors where ventilation is limited.

Radon is chemically inert, meaning it does not react with other substances. However, it is radioactive and decays into radioactive particles known as radon progeny (or radon daughters). When inhaled, these particles lodge in the lung tissue and emit radiation that can damage DNA over time — ultimately leading to lung cancer.

How Radon Forms

Radon (specifically Radon-222) is part of the natural uranium decay chain. Uranium decays into radium-226, which then decays into radon-222. This process happens continuously in soil and rock throughout the Earth's crust. The radon gas moves through pores and cracks in soil and rock and can rise to the surface and enter the atmosphere — or enter buildings through foundation gaps.

Certain geographic areas have higher concentrations of uranium and radium in the soil, resulting in higher radon levels. The EPA's radon zone map identifies regions of the United States with elevated radon potential. However, radon can be found in dangerous concentrations in homes in every state — no region is completely safe.

The EPA's Findings: A Leading Cause of Lung Cancer

The U.S. Environmental Protection Agency (EPA) estimates that radon exposure causes approximately 21,000 lung cancer deaths per year in the United States. That makes radon the second leading cause of lung cancer, behind only cigarette smoking. For non-smokers specifically, radon is the leading cause of lung cancer.

The risk compounds significantly when radon exposure is combined with smoking. A smoker living in a high-radon home faces a dramatically higher lifetime risk of lung cancer than either factor alone would suggest. The Surgeon General and the EPA both recommend testing every home for radon.

How Radon Enters Your Home

Radon enters homes through any opening where the house contacts the soil. Common entry points include:

• Cracks in concrete floors and walls
• Construction joints where floor meets wall
• Gaps around service pipes (water, gas, electrical)
• Cavities inside walls
• Gaps in suspended floors above crawl spaces
• Well water (radon can be released from water into indoor air)

The pressure inside a home is typically slightly lower than the pressure in the soil around the foundation. This pressure difference acts like a vacuum, drawing radon-laden air up through openings in the foundation. This is why lower levels of a home — basements and crawl spaces — tend to have higher radon concentrations.

Who Is Most at Risk?

Anyone spending significant time in a high-radon home is at risk, but some groups face elevated danger:

• Smokers — the combination of radon and tobacco smoke dramatically amplifies lung cancer risk
• Children — spend more time at home and have faster respiratory rates, increasing radon exposure
• People who work from home — longer time spent indoors means longer exposure periods
• Basement dwellers — those who sleep, work, or spend significant time in lower levels of the home

What You Should Do

Because radon is invisible and odorless, the only way to know if your home has elevated levels is to test. The EPA recommends that all homes below the third floor be tested for radon. Testing is inexpensive, straightforward, and can be done with a DIY kit or by a certified professional.

If your test shows levels at or above 4 pCi/L, a radon mitigation system can reduce indoor radon levels by up to 99%. Mitigation is typically a one-time installation costing $800–$2,500 that provides long-term protection for your family.