A city just outside of San Francisco has unanimously voted to ban fifth-generation (5G) cellular towers, claiming that they pose a significant threat to public health.

In an urgency ordinance, Mill Valley city council voted earlier this month to block deployments of 5G towers and small cells (smaller, lower powered cellular radios used to expand cellular coverage) in residential areas.

The city council says it was motivated, in part, by locals who expressed concern about the “serious adverse health and environmental impacts caused by the microwave radiation emitted from these 4G and 5G Small Cell Towers.” The ordinance was in response to recent FCC efforts to speed up 5G network deployments at the behest of wireless carriers looking to modernize their networks. While the importance of these upgrades has at times been overhyped by industry, the upgrades should ultimately provide consumers with faster, more resilient wireless networks. But a contentious debate over the width and breadth of cellular radiation on human health has raged since the 1980s. And while the internet is full of claims of significant risk caused by cellular radiation, numerous organizations continue to insist the scientific evidence supporting a link between cellular radiation and cancer remains unproven.

“There is no scientific evidence that provides a definite answer to that question,” the CDC website states. “Some organizations recommend caution in cell phone use. More research is needed before we know if using cell phones causes health effects.”

Others don’t believe there’s any meaningful risk.

“I don’t think there’s any convincing evidence that cell phones or cell phone signals cause cancer or any other disease,” doctor and medical author Christopher Labos told Motherboard. “If you want to argue that they do than you have to explain the many negative studies showing that they don’t.” Labos argued that a major Danish study, the so-called Million Women study, and previous CERENAT and CEFALO studies all show no solid evidence of human health risks. He stated that while an 11-country INTERPHONE study is sometimes cited on some fronts as evidence supporting proof of cancer risk, the author’s conclusion was that “no increase in risk of glioma or meningioma was observed with use of mobile phones.” As you might expect, the wireless industry has also denied any potential health hazards from cellular radiation.

“The FCC, the FDA, the World Health Organization, the American Cancer Society and numerous other international and US organizations and health experts continue to say that the scientific evidence shows no known health risk to humans due to the RF energy emitted by antennas or cell phones,” said the CTIA, the wireless industry’s biggest policy and lobbying group.

“The evidence includes analysis of official federal brain tumor statistics showing that since the introduction of cellphones in the mid-1980s, the rate of brain tumors in the United States has decreased,” the CTIA told Motherboard.

Dr. David Carpenter, Director of the University of Albany's Institute for Health and the Environment, is more of a true believer. He directed Motherboard’s attention to two recent studies showing a slight increase of tumors in male rats who were exposed to cellphone radiation nine hours a day daily for two years.

Carpenter says that the risk posed to human health is real, and will only be amplified by additional cellular towers and small cell deployment, basking human beings in radiofrequency electromagnetic fields (EMFs).

“You will not be able to walk down a sidewalk without being continuously exposed to elevated levels of EMFs,” Carpenter said in an email to Motherboard. “EMFs cause cancer in both humans and animals, interfere with human reproduction and triggers a syndrome of electrohypersensitivity in some individuals, characterized by headache, fatigue and cognitive dysfunction.”

But some researchers have long argued animal studies often aren’t directly applicable to a better understanding of human health. The rat studies also were somewhat inconsistent, with female rats not showing the same results as male rats. Claims of electromagnetic hypersensitivity have also not held up in the face of double blind experiments.

That said, it’s also clear there’s a lot we still don’t fully understand. It’s still too early to tell whether 5G deployment and small cells complicate things, according to Dr. Jerry Phillips, a professor at the Department of Chemistry and Biochemistry at the University of Colorado. Phillips said studies taking a specific look at the health risks of 5G technology are virtually nonexistent, and that the risk of cumulative radiation exposure also needs a closer look. “Of concern here are not just the potential effects of 5G-associated radiation, but what might result from the combined impact of 5G-radiation with other sources of non-ionizing radiation in our environment,” Phillips said. “Certainly, a more careful and thorough assessment of the risks to human and environmental health are warranted.”