Just about every dental health professional agrees that brushing your teeth at least twice a day is a good rule of thumb, but the contents of toothpaste stir a little more controversy. (Don’t even get us started on the whole is-flossing-really-worth-it debate.) The most contentious ingredient in toothpaste is fluoride.

A naturally occurring mineral that has been added to drinking water for decades, fluoride is also an ingredient in many, many adult toothpastes. On the one hand, mainstream dentists generally embrace it as a serious cavity fighter. In fact, the American Dental Association firmly supports fluoridation of water and won’t put its seal of approval on any toothpaste that doesn’t contain it.

And yet over the years, a smaller group of holistic dentists have raised concerns about potential neurotoxicity of fluoride in drinking water and toothpaste. In 2014, top medical journal The Lancetdesignated the mineral as a neurotoxin in 2014, leading federal health officials—for the first time in more than 50 years—to advise local governments to lower the amount of fluoride in the U.S. water supply.

While too little fluoride is linked to tooth decay, a recent study found that drinking water might actually contain too much of it, which could cause dental and bone disease—especially in children. But here’s the good news: researchers recently developed a new, portable device, SION-105, to measure the fluoride levels of water with just a few drops. What makes this so major is that it allows groundwater to be tested to ensure drinking water in various cities is, in fact, safe.

But what about fluoride in toothpaste? We asked two dentists with different opinions to weigh in on what you should squeeze onto your toothbrush every day.

The case against fluoride:

Around 17 years ago, Bruno Sharp, DDS—a fourth-generation dentist with a practice in Florida—began digging into the criticism of the old-school oral health ingredient. What he found, he says, it alarming.

“The effects of fluoride haven’t been known to most dentists, therefore most dentists still believe that it’s beneficial,” says Dr. Sharp. But it is a potential neurotoxin, he argues, and can accumulate in the body over time.

Indeed, mainstream medical groups like the Mayo Clinic warn about the dangerous side effects of overdosing on sodium fluoride, though it adds that taking it as a supplement or drinking it in tap water does not usually cause any of those issues. And yet, the Environmental Protection Agency has also said it’s likely some children are exposed to too much fluoride “at least occasionally.”

For Dr. Sharp, it’s just not worth the risk for anyone, especially because he’s not convinced by the science supporting fluoride’s efficacy in treating cavities.

A 2015 Cochrane review found, for example, that fluoridated water simply didn’t have any cavity-fighting benefits for adults specifically. Much of the science supporting fluoridation is decades old. “Adults and children,” he says, “should be aware of the research and data available out there.”

Dr. Sharp does believe that patients with oral cancer requiring radiation do benefit from fluoride. But beyond that, he’s convinced there’s no compelling reason for it to be in toothpaste.

The benefits of fluoride:

New Jersey-based dentist Alexander Rubinov, DDS, is totally in favor of fluoride when it comes to topical applications like toothpaste. It’s absorbed into the tooth’s enamel, he explains, and helps repair it by replenishing lost minerals. In other words, it helps to keep teeth strong.

That said, Dr. Rubinov fully acknowledges that fluoride can be dangerous in really high amounts. “I don’t want to discredit all the research that’s been done that has indicated fluoride is, indeed, toxic in a certain dose,” he says. But you won’t get that dose from your toothpaste. (You should not be swallowing toothpaste.)

All that said, if you generally have good dental hygiene—you drink a lot of water, avoid sugary drinks, and you brush and floss every day—it probably doesn’t matter if you want to skip fluoride, he says.

As he explains, “It’s really most important for people who aren’t compliant with good oral health care.” In other words: Keep up a spot-on dental routine and you might not even have to worry about fluoride.

Originally published April 18, 2017. Updated February 13, 2019.

Want to dig into some other wellness controversies? Here’s how to know if six-week workout challenges are really worth it, and whether micro-dosing LSD might make you happier.