Is there a threshold of exposure below which radon levels are considered harmless?

Radon is a radioactive gas that originates from the decay of uranium in the soil, rock, and water. It is vital to understand that there is no threshold level of radon exposure that is universally considered completely harmless. The health risks associated with radon exposure increase with higher levels of radon and longer durations of exposure. Regulatory bodies, such as the Environmental Protection Agency (EPA), state that levels below 4 picocuries per liter (pCi/L) are considered acceptable, but they also emphasize that no level of radon is entirely safe.

Even low levels of radon can pose health risks, particularly in terms of lung cancer. The risk is cumulative, meaning that prolonged exposure—even to low levels—can increase the potential for developing health issues over time. Consequently, while some may argue that certain low radon levels might be tolerable, public health guidelines recommend reducing radon exposure as much as possible to mitigate health risks, reinforcing the notion that there is no truly "harmless" level of radon exposure. This is why the assertion that there is a threshold below which radon levels are considered harmless is not accepted by health organizations and is deemed false.