Most communities in the U.S. add fluoride to the tap water. It has been common practice for nearly 80 years to protect against tooth decay and cavities, and it’s considered a major achievement in public health. The Centers for Disease Control and Prevention says research shows that community water fluoridation reduces cavities by around 25%.

It has also long drawn opponents who have raised concerns about the practice, ranging from evidence-based concerns to unsubstantiated conspiracy theories. The debate heated up recently when President-elect Donald Trump picked Robert F. Kennedy Jr. to lead the Department of Health and Human Services. Kennedy is a longtime anti-vaccine activist who has also been outspoken in opposing water fluoridation, and if he’s confirmed in the role, he could influence policy.

This week, government scientists published a paper in the medical journal JAMA Pediatrics that has added to the debate. It is the analysis behind a 300-page report released last August from the National Toxicology Program, part of the National Institutes of Health.

That report concluded with “moderate confidence” that there may be a link between high levels of fluoride exposure and lowered IQ. This could indicate possible neurodevelopmental harms to pregnant people or young children, when they are exposed to drinking water containing at least 1.5 milligrams of fluoride per liter — a level more than twice what’s recommended (0.7 mg/L) for the U.S. water supply.

Monday’s analysis digs deeper into the data behind these conclusions. It looks at a few dozen foreign studies that other researchers have conducted, mostly in China and India, and finds an association between high levels of fluoride and a small decrease in children’s IQ.

“There were not enough data to determine if 0.7 mg/L of fluoride exposure in drinking water affected children’s IQ,” Christine Flowers, director of the Office of Communication at the National Institutes of Health, wrote in an email.

While the conclusions are consistent with the August report, the timing of the paper, released weeks before Trump takes office, gives it renewed prominence. The report’s contents were given “substantial weight” in a recent federal court ruling that ordered the Environmental Protection Agency to address potential risks posed by fluoride levels.

The analysis is controversial. The paper was published alongside two editorials in JAMA Pediatrics. One, by Steven Levy, a public health dentist at the University of Iowa, questioned the analysis’s methods and disagreed with its conclusions. The other, by a trio of children’s health researchers, supported its findings.

Using this analysis — which is inconclusive at levels of fluoridation below 1.5 mg/L — to inform the debate over low levels of fluoride in drinking water feels like a stretch to fluoridation supporters like Levy.

“The major problem is that the science is not as strong as it’s presented by these authors,” he says. For instance, the study authors write in the paper’s abstract that fluoride exposure seems linked (in certain studies) with lower IQ at levels even below 1.5 mg/L, but Levy notes that the data they provide aren’t conclusive.

Also, Levy says the authors didn’t fully consider some recent research that casts doubt on the links between fluoride exposure and IQ. He says there’s sometimes a pattern in public health research in which some initial studies suggest a problem, but over time, as the problem gets better studied, “the evidence goes in a somewhat different direction.” He points out that some of the more recent fluoride studies, which he thinks are better designed, found no negative effect on IQ, and he thinks they should have been given more weight in the recent analysis.

To others, the analysis published this week makes a strong enough case out of imperfect evidence for action. “What the study does, or should do, is shift the burden of proof,” says Dr. Bruce Lanphear, a children’s health researcher at Simon Fraser University, who co-authored the other editorial, which supported the paper’s findings. “The people who are proposing fluoridation need to now prove it’s safe.”

Lanphear agrees with concerns, raised by the study authors, that the base level of fluoridation, plus the myriad other sources of fluoride in people’s lives — such as toothpaste, mouthwash, and food and drinks, including some teas, fruits, vegetables and seafoods — could be pushing fluoride to harmful levels in some vulnerable people.

“There is concern that pregnant women and children are getting fluoride from many sources … and that their total fluoride exposure is too high and may affect fetal, infant, and child neurodevelopment,” wrote the NIH’s Flowers.

And while water fluoridation does clearly prevent cavities, Lanphear says the relative benefits have declined in the past few decades since people started using fluoridated toothpaste, a point supported by a recent analysis by U.K. researchers.

“There are other ways we can protect children from developing cavities,” he says. “We could, for example, regulate sugary beverages … [or] have programs to help children learn to brush their teeth more effectively.”

It’s time to reassess the potential risks of fluoride against its benefits, Lanphear says.

Those benefits are substantial and so common that they’re taken for granted, says Levy. But “it isn’t that cavities are under control for everyone,” he says. Fluoridated water most benefits those who are poor and underserved, who might not have fluoridated toothpaste or regular access to dental care.

And while cavities can be prevented in other ways, “those alternatives are for much more costly things,” Levy says. “Even [providing] fluoride toothpaste for individuals would be 10 to 20 times more costly than water fluoridation. Using fluoride mouth rinses or going to the dentist to get fluoride treatments would be much more expensive.”

Levy would like to see more high-quality research on the topic before long-standing policies get upended. But even without more scientific clarity, the debate is likely to escalate. The Environmental Protection Agency is facing a late-January deadline, should it appeal the federal court decision ordering it to reduce fluoride risks.

And Robert F. Kennedy Jr. will soon face confirmation hearings where he may have to answer direct questions about views he has aired on fluoride in the past.

Los Angeles firefighters have made big gains in battling the Sunset fire, which had triggered mandatory evacuation orders in Hollywood and the Hollywood Hills late Wednesday.

“It’s a miracle that no homes burned here,” one firefighter told The Times. Hours earlier, the flames had approached the mansions that line North Curson Avenue. By 10:30 p.m., flames were barely visible on the distant hillside.

“These are really nice houses up here,” one firemen said to another as they watched a helicopter fly by to drop water. Firefighters on scene said the fire had been 50 acres at its peak, and was now down to 42.3 — in retreat.

The blaze, for a short while, raised alarms throughout Hollywood. A mandatory evacuation order was issued around 5:30 p.m. for areas north of Hollywood Boulevard and south of Mulholland Drive, and east of Laurel Canyon Boulevard and west of the 101 freeway.

The was reported at 2350 N. Solar Drive in the Hollywood Hills.

The evacuation encompassed iconic locations such as the TCL Chinese Theatre, the Hollywood Pantages Theatre, the Dolby Theatre, and Ovation Hollywood, the shopping center in Hollywood.

Earlier Wednesday, David Potts, 66, stood on his front porch just a few hundred yards from the active fire, a fire truck parked directly opposite him.

Just up the hill, the crackle of flames punctuated the low hum of engines and flowing water. Every seven minutes or so, another helicopter came by and dropped water which sprinkled over the neighborhood. He stopped to see if the water had extinguished a burning tree he could see from his perch.

His home of 11 years sits next to Runyon Canyon. Around 4:30 p.m., he saw a nearby fire on the news and stepped outside to a thick smell of smoke. He could see the flames just a few hundred yards up the hill, with one property between him and the blaze.

When the mandatory evacuation notice came shortly thereafter, his wife, daughter and son-in-law quickly packed and left.

It took them two hours amid the chaos to drive to Glendale, but David stayed and got out his hose.

“A friend lost his house this morning in Altadena and I figured I would stay until the last minute,” he said.

He packed up his truck with essentials and started spraying his house and yard.

For a while, no help arrived. “Right as I was about to throw in the towel, two helicopters came,” he said. They dropped water and he saw a white cloud of steam which sent embers flying everywhere.

He kept hosing: “I could see progress from the helicopters.”

Potts knows his neighbors well, he said, and all left except for him. It fell to him to text them updates while he scrambled to find a mask, get his ladder and continuously spray everything he could reach.

Later on Wednesday, at the base of Curson Avenue — a snaking street that climbs from Franklin Boulevard into the hills adjacent to Runyon Canyon — some 50 people stood at the police line, some wearing masks and most wielding smartphones to capture the firefight. At one point, the hillside was lightly glowing.

Firefighters and residents alike credited the efficient water dropping for stemming the blaze. The nearby Hollywood reservoir allowed for frequent trips, a firefighter said. By 10:30 p.m., the water drops were happening around every ten minutes. A Times reporter could feel the drizzle of water from the water drops as the last remnants of fire could be seen from his location.

Up the hill, some firefighters stood watch as others walked hundreds of yards above with chainsaws and garden tools, cutting a fire line near the peak of Runyon Canyon. Their flashlights swung left to right as around a dozen men walked single file across the hilltop.

Most of the mandatory evacuation area was lifted except for a few city blocks, affecting areas north of Franklin Avenue, west of Camino Palmero Street and east of Sierra Bonita Avenue. Firefighters wanted the area to stay under evacuation orders to ensure vegetation in the area does not flare up.