Radon: The Invisible Home Health Hazard Millions Don't Know About

What Radon Is and Where It Comes From

Radon is a radioactive gas produced by the natural decay of uranium, an element found in varying concentrations in soil, rock, and groundwater across the United States. As uranium breaks down into radium, and radium further decays, radon gas is released into the surrounding environment. Outdoors, it disperses harmlessly into the atmosphere. The problem begins when it accumulates inside enclosed spaces — particularly homes.

Because radon has no color, odor, or taste, it gives no sensory warning of its presence. A home can have dangerously elevated radon levels while appearing and smelling completely normal. This invisibility is precisely what makes it a significant household concern that often goes unaddressed for years.

Radon is present in outdoor air virtually everywhere on Earth, typically at very low concentrations (around 0.4 pCi/L on average). It's only when it becomes trapped and concentrated indoors that health risks increase substantially.

How Radon Enters Your Home

The path radon takes into a home is driven largely by pressure. Homes tend to have slightly lower air pressure than the surrounding soil, which creates a vacuum effect that draws soil gases — including radon — inward. Common entry points include:

• Cracks in concrete floors and walls
• Gaps around service pipes and utility penetrations
• Construction joints where different materials meet
• Sump pits and floor drains
• Crawl spaces with exposed soil

Basements and lower floors tend to have the highest concentrations because they are closest to the soil. However, radon can migrate upward through a home and reach significant levels on upper floors as well. Well water sourced from rock can also release radon when used indoors, though this is a less common pathway than soil entry.

For a broader look at how structural features affect home safety, see our room-by-room home safety audit, which covers a range of hazards by location.

The Health Concern: Why Radon Matters

Radon itself is not directly inhaled into tissue in a harmful way — the problem is what it decays into. When radon breaks down, it produces short-lived radioactive particles called radon progeny (or decay products). These particles can attach to dust and aerosols in the air, be inhaled, and become lodged in the lungs. Over time, the radiation they emit can damage lung tissue.

The U.S. Environmental Protection Agency identifies radon as the second leading cause of lung cancer in the country, responsible for an estimated 21,000 deaths annually. The risk is significantly compounded by cigarette smoking — smokers exposed to elevated radon levels face a substantially higher risk than non-smokers at the same concentration.

“Radon is estimated to cause about 21,000 lung cancer deaths every year. Although you can't see or smell radon, it's not difficult to test for, and if high levels are found, you can take steps to fix the problem.”

— U.S. Environmental Protection Agency, Federal environmental and public health regulatory agency

This article provides general educational information about radon. It is not a substitute for guidance from a qualified health professional, certified radon specialist, or your local public health authority.

Radon risk belongs in the same conversation as other invisible indoor air threats. Our article on carbon monoxide in the home covers another colorless, odorless gas that presents serious household risks.

Testing and Reducing Radon in Your Home

Testing is the essential first step — and it's straightforward. Two main options exist for homeowners:

1. Short-term tests (typically 2–7 days): Charcoal canister kits are widely available. They provide a snapshot reading and are a reasonable starting point, though results can vary with weather and seasonal changes.
2. Long-term tests (90 days or more): Alpha track detectors give a more representative average over time and are generally preferred for confirming whether action is needed.

The EPA recommends testing in the lowest level of the home that is regularly used — a finished basement used as a living area, for example. If initial results are at or above 4 pCi/L, the EPA advises mitigation. Between 2 and 4 pCi/L, mitigation is worth serious consideration.

The most common and effective mitigation approach is sub-slab depressurization: a pipe system draws radon from beneath the foundation and vents it safely outside before it can enter the living space. This method is typically installed by a certified radon mitigation contractor and can dramatically reduce indoor levels. After mitigation, follow-up testing confirms the system is working.

For homeowners thinking holistically about household air quality, our overview of indoor air quality covers the broader range of pollutants that can affect a home's environment.

This article is for general informational and educational purposes only. It is not medical advice. For concerns about radon exposure or lung health, consult a qualified healthcare professional. For radon testing and mitigation guidance, contact a certified professional or your state radon office.