Charcoal toothpaste may be having a moment as a go-to brightening and whitening tool, but some dentists say these products might actually damage tooth enamel and make cavities more likely.

At a minimum, any claims charcoal toothpaste marketers make have no scientific evidence behind them, the authors of a paper in the British Dental Journal warn. "The evidence highlighting any potential benefits of charcoal toothpaste over regular toothpaste is severely lacking," said Dr. Joseph Greenwall-Cohen of the University of Manchester Dental School in the UK, one of the coauthors. "In general, I would encourage all people to stick to regular toothpaste over charcoal toothpaste," Greenwall-Cohen said.

A wide variety of charcoal toothpastes and tooth powders are available on store shelves, and packaging often claims that these products are "natural" or "eco-friendly" or have "antibacterial" or "antifungal" properties, the paper notes. This may persuade consumers they're buying something good for the environment that can also help prevent or treat gum disease or other oral health problems.

"There is simply no scientific proof that these products are capable of detoxifying your mouth, offer any increased antimicrobial activities (antibacterial, antifungal, antiviral), or can fortify/remineralize/strengthen tooth structure," said Dr. John Brooks, a researcher at the University of Maryland School of Dentistry in Baltimore who wasn't involved in the paper.

There's an outside chance that charcoal toothpaste might lure some people with poor oral health habits to suddenly start flossing and brushing after every meal, and if this happens it could be considered one benefit of these products, Greenwall-Cohen and colleagues write.

But the problem is that people with poor oral hygiene who try charcoal toothpaste may actually find it damages their tooth enamel or increases their risk of cavities, they warn.

Not much research to date has tested the safety and effectiveness of charcoal toothpaste against alternatives in head-to-head clinical trials.

Some small studies looking at the effects of charcoal toothpaste have, however, found that it may be too abrasive to tooth enamel. Charcoal may erode the outer layer of enamel on teeth, exposing interior tissue and increasing the risk of tooth decay, some of these studies suggest.

Charcoal may also cause cancer, Brooks, who has done research on charcoal toothpaste, said by email.

"I have concerns about the chronic exposure of the oral mucosa (tissue) to charcoal as the federal government has classified charcoal as a carcinogen," Brooks said. "Another potential health concern we uncovered was that one-third of the 50 brands of charcoal toothpaste we investigated included bentonite clay, a mineral that may contain crystalline silica, another recognized carcinogen by the federal government," Brooks said.

When consumers do seek out specific toothpaste ingredients, fluoride is what matters most, dentists say. Plenty of research has found brushing with a toothpaste that contains fluoride can help prevent tooth decay and cavities.

"None of the charcoal toothpastes would likely offer any cavity-fighting potential any more than brushing with non-fluoride toothpaste," Brooks said.