Radon is a naturally occurring radioactive gas that forms from the breakdown of uranium found in soil and rock. The gas seeps from the ground and becomes trapped inside enclosed spaces like houses, leading to elevated concentrations in indoor air. While radon is the second leading cause of lung cancer, exposure does not cause acute sickness or immediate symptoms, but instead poses a long-term risk of developing lung cancer.
Why Radon Exposure Causes No Immediate Symptoms
Unlike carbon monoxide, radon is chemically inert and does not react with the body’s tissues when inhaled. The gas is odorless, colorless, and tasteless, making it impossible to detect without specialized equipment. Because it is a gas, it passes through the lungs and is exhaled, causing no acute physiological response like dizziness or coughing. This lack of sensation means a person can be exposed to high levels for years without immediate indication of a problem.
The danger is tied to chronic, low-level exposure over a significant period of time, not a sudden toxic event. Symptoms sometimes associated with “radon poisoning,” such as a persistent cough, are actually signs of lung cancer that develop years later, not a reaction to the gas itself.
The Biological Mechanism of Latent Harm
The delayed effect of radon exposure requires time to cause cellular damage. When radon gas is inhaled, it quickly decays into solid, short-lived radioactive particles, known as radon progeny, which include elements like polonium, lead, and bismuth. These solid decay products attach to dust particles and aerosols in the air, and when inhaled, they become lodged in the lining of the lungs and airways.
The harm is caused by these lodged solid particles, which emit high-energy alpha radiation. Alpha particles are heavy and deposit a large amount of energy over a very short path, damaging the DNA of the surrounding lung cells. This radiation-induced damage can cause mutations in the lung tissue, but it takes an extended period for these damaged cells to turn cancerous. This delay between the initial DNA damage and the emergence of a tumor is called the latency period, which commonly ranges from 5 to 25 years.
Quantifying Risk Through Testing and Action Levels
Because the risk is long-term and exposure is undetectable by human senses, quantifying the risk requires specialized testing. Radon levels are measured in units of picocuries per liter of air (pCi/L). This measurement represents the rate of radioactive decay occurring in a given volume of air.
The U.S. Environmental Protection Agency (EPA) has established an action level of 4.0 pCi/L, recommending that homeowners take steps to reduce radon if the levels meet or exceed this threshold. No level of radon is considered completely safe, and the EPA suggests considering action if levels are between 2.0 and 4.0 pCi/L.
Testing can be done using short-term kits, which measure levels over a period of 2 to 90 days, or long-term kits, which monitor for more than 90 days. Long-term testing is generally preferred because it provides a more accurate annual average exposure, accounting for natural fluctuations caused by seasonal changes and weather.
Immediate Steps for Reducing Exposure
Once elevated radon levels are confirmed through testing, steps should be taken to reduce the concentration in the home. One initial action is to seal major entry points where the gas can infiltrate the structure, using caulk to seal visible cracks in the foundation floor, walls, and gaps around utility pipes. Sealing alone is generally not sufficient to consistently lower high radon levels, but it improves the effectiveness of other mitigation techniques.
The most reliable long-term solution is the installation of an active sub-slab depressurization system, also known as a radon reduction system. This system uses a vent pipe and a continuously operating fan to draw radon gas from the soil beneath the foundation slab before it can enter the house. The fan safely exhausts the gas outside and above the roofline, creating a vacuum beneath the home to prevent intrusion. Increased ventilation, such as opening windows, can also provide a temporary reduction in radon levels.