Radon risk maps prompt action in high-risk areas but may backfire in low-risk ones

Radon is the second leading cause of lung cancer after smoking, responsible for approximately 21,000 deaths in the United States each year. It is also colorless, odorless, and tasteless. Without testing, homeowners have no way to know it is present. Yet testing rates remain low, and a persistent challenge for public health communicators is how to convey risk for something invisible.

Maps that show geographic radon risk levels seem like an obvious solution. But a study from the University of Oregon, published in Public Health, finds the reality is more nuanced: maps work well for people already in high-risk areas and may actually diminish concern among those living where risk is lowest.

Study design: nine maps, 2,000 households

The research team collaborated with the British Columbia Centre for Disease Control to design nine different radon risk maps, each presenting the same underlying risk data in a slightly different format. One map used simple low-medium-high labels; another displayed actual average radon concentrations by area; others varied color schemes, geographic granularity, or accompanying text.

These maps were distributed through an online survey to 2,000 British Columbia residents. Each participant answered questions about their prior radon knowledge and testing history, then viewed one randomly assigned map. After reviewing the map, they reported their intentions to test their home for radon. The study also collected smoking status, since smokers face compounded risk from radon exposure - radon and tobacco smoke act synergistically to damage lung tissue.

What the data showed

"The type of map didn't matter so much as just seeing the map," said lead author Cathy Slavik, who conducted the research as a Banting Postdoctoral Fellow at the University of Oregon and is now an assistant professor at Simon Fraser University. Format differences between the nine maps had minimal effect on testing intentions. Whether the map used labels or numbers, simple or detailed presentation, participants responded similarly.

What did matter was the risk level of where the participant lived. In medium-high and high-risk areas, seeing any map significantly increased testing intentions, regardless of which map format participants viewed or whether they smoked. The map functioned as an effective prompt: it made an abstract risk concrete and local.

In low-to-medium-risk areas, however, maps made no detectable difference to testing intentions. And in the lowest-risk areas, testing intentions among nonsmokers actually decreased slightly after viewing a map. A likely explanation is that people interpreted "low risk" as meaning they had no reason to act - the map provided reassurance rather than motivation, even though any home can accumulate radon regardless of area risk levels, and even low-level exposure carries some health risk over many years.

Unintended meaning

"Those low-risk people, and particularly nonsmokers who are at even lower risk, they found meaning in the maps that was unintended," said Ellen Peters, director of the Center for Science Communication Research at the University of Oregon. Risk communication research has long documented that people are prone to binary interpretation - "low risk" gets read as "safe" rather than "lower probability but not zero."

Slavik suggests that different communication strategies may be needed for different risk zones. Maps work as intended in high-risk areas, where the message and the response align. In low-risk areas, messaging that emphasizes the universality of radon risk, the ease of testing, and the potential for any home to accumulate radon may serve better than a geographic map that inadvertently signals safety.

Limitations and broader applications

The study used hypothetical testing intentions rather than actual testing behavior. Whether stated intentions translate into behavior is always uncertain, and the gap between intention and action tends to be larger for actions that require effort, cost, or scheduling. The survey was also conducted in British Columbia, a specific regulatory and cultural context, and Canadian attitudes toward radon risk may differ from those in other countries.

Slavik plans to extend the framework to wildfire smoke risk communication, which shares key features with radon: the risk can be present even when the hazard is not visible or directly sensed, and low-level exposure carries cumulative health consequences that are easy to discount.