Woe be to the Environmental Protection Agency. If President Trump gets his way, the federal agency will lose 31 percent of its annual budget—about $3 billion. Supporters of Trump’s 2018 budget proposal call it a “back to basics” approach, carving away what they see as the agency’s regulatory overreach. Opponents are similarly pithy: The EPA’s former director labeled Trump’s proposal a “scorched Earth budget.”

Disagreements over the utility of the EPA's programs typically fall along the partisan lines you might expect. But not all of them.

At least one of Trump's proposed budget cuts targets a program that some scientists have been questioning for decades: residential radon risk. That program, which sets the standards for risk and protection from radon gas, would be completely zeroed out. Now, according to the EPA, the WHO, and many other big public health organizations, radon is second only to cigarette smoking as a leading cause for lung cancer. The EPA says radon gas causes 21,000 deaths every year. Yet some critics in the health care profession say that’s all baloney.

Trump's budget hasn't passed. It still has to survive the congressional gauntlets, full of many senators and representatives who have already voiced opposition to many of the EPA cuts, including to the radon program. But some scientists might actually want the EPA to back off on this one.

The issue here isn't whether radon causes cancer. It does, certainly. But critics say scientists can only prove that radon is carcinogenic at high doses. Like, rates typically found in mine shafts, not suburban homes. They add that the established scientific method for establishing low-dose radon risk assessments is simply unscientific. Some even go so far as to say low doses of radiation might help your body fight cancer. Follow that logic through, and they say the EPA's low dose radon risk assessment could actually be harming people.

It's Coming from Inside the House

Radon is radioactive gas emitted when uranium decays. And because most rocks contain traces of uranium, it leaks from the soil virtually everywhere on Earth. Like uranium, radon decays, too. If it does this in your lungs, the alpha particles it releases can harm the DNA in your cells. "When we talk about radon risk, we really mean the risk from radon and its decay products," says Phillip Price, a physicist at Lawrence Berkeley National Laboratory. If enough DNA gets damaged, the mutations pile up and … lung cancer.

Radon is everywhere, but it doesn't usually pose much of a risk because it disperses into the open air. "What’s unnatural are the radon levels that accumulate indoors,” says James McLaughlin, president of the European Radon Association.

Scientists began to recognize the threat in the 1970s, when epidemiologists found that miners were getting lung cancer at higher-than-average rates. The tunnels they worked in were full of radon gas. But the agency's real work started after 1984, when an engineer at the Limerick Nuclear Power Plant in Pennsylvania set off radiation alarms as he was coming in to work. After some sleuthing, public health experts figured out that his house was filled with radon. Like, uranium mine levels of radon. This set off a national panic—homeowners feared their home might have similarly high levels.

By 1986, the EPA established an indoor radon risk exposure level—4 picocuries per liter of air. It's similar to that recommended by the World Health Organization and the European Union. That number isn't tied to any regulations: Instead, the EPA recommends that people test their homes (which can cost between $20 and $200) and take action if necessary—say, by installing fans and vents to improve airflow. Hiring a contractor to ventilate your basement can run into the thousands.

Radon? Maybe Radon't

That number, 4 picocuries, is a funny one. Because here's the thing: The scientific model used to come up with that limit says there's no acceptable level of radon exposure. None.