Does charcoal toothpaste really whiten teeth?

Will this toothpaste make your smile shine?

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People looking for a whiter smile might reach for charcoal toothpaste, given its claims of being "natural" and its long history. But does charcoal toothpaste really whiten teeth? And does it do so safely?

The answer is mixed. While charcoal toothpaste can brighten your smile a little, it's not the best whitening agent out there. Nor is it the safest option available, Dr. John Brooks, a clinical professor in the Department of Oncology and Diagnostic Sciences at the University of Maryland School of Dentistry, told Live Science.

Those in pursuit of pearly whites have used charcoal for oral hygiene since Hippocrates recommended it to his fellow Grecians, according to a 1992 study in the British Dental Journal. In the 1930s and 1940s, American manufacturers touted charcoal chewing gums and powders that they claimed would freshen and whiten, a 2017 commentary in the Journal of the American Dental Association noted. Today health- and eco-concerned consumers can find floss, toothpaste, mouthwash and even toothbrushes infused with activated charcoal that promise to whiten teeth and "detoxify" mouths.

Granted, activated charcoal is a well established treatment for some poisons and acute overdoses. Common charcoal is made from materials such as peat, coal and wood, but making activated charcoal involves the additional step of heating regular charcoal in the presence of a gas. "This process causes the charcoal to develop lots of internal spaces or 'pores,'" which helps activated charcoal "trap" chemicals, according to MedlinePlus, a site run by the U.S. National Library of Medicine.

Many manufacturers claim that the tiny pores in activated charcoal can similarly "detoxify" your mouth and remove stains from teeth. A 2017 review of charcoal-based toothpastes published in the Journal of the American Dental Association found that 96% of charcoal toothpastes claimed to have whitening benefits and 46% boasted the ability to detoxify teeth. One problem: There is no scientifically agreed-upon definition of what it means to detoxify something, or at least not a mouth. And these claims are largely unsupported by evidence. Even more concerning, the safety and toxicity of these charcoal-based dental products hasn’t been tested, Brooks wrote in the review of charcoal-based toothpastes.

"We are concerned [that these products are] injurious to the teeth," Brooks, lead researcher of the 2017 review, told Live Science. In a 2019 study in the Journal of Applied Oral Sciences, researchers stained 90 cow teeth with concentrated black tea and then applied several teeth-whitening agents to them to see which performed best. Although activated charcoal wasn't the top performer (that honor went to blue covarine, a whitening agent that works by coating the enamel in a film, temporarily making them appear whiter), it did result in some whitening after four weeks, the researchers found.

However, one small study is not sufficient evidence to prove charcoal is an effective or safe dental product. In fact, Brooks and many other practitioners are concerned that charcoal's abrasive particles achieve whitening by removing a layer of enamel — the hard outer surface on teeth that helps prevent decay — which may effectively weaken teeth and make them more vulnerable to further yellowing, Brooks said.

Brooks also warned that charcoal contains at least four hydrocarbons that are recognized by the U.S. federal government as likely carcinogens. There’s epidemiological evidence that charcoal-grilled meat is linked to certain types of cancer. One-third of the charcoal-based toothpastes also contain bentonite clay, which can be carcinogenic too. His concern is that some people will go to the extreme, using charcoal products more often than recommended in the hope that they'll get a pristine smile. In these cases, chronic exposure could be dangerous, especially because the toxicity of these products is untested, Brooks said.

But even these options are "not innocuous," he said. After using a whitening treatment, people "can develop short-term sensitivity and gum irritation," Brooks said. Rather than thinking in terms of whitening your teeth, the best way to avoid side effects from whitening products is "not eating and drinking things that darken the teeth in the first place," such as red wine, tobacco and coffee, Brooks said.

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Donavyn Coffey is a Kentucky-based health and environment journalist reporting on healthcare, food systems and anything you can CRISPR. Her work has appeared in Scientific American, Wired UK, Popular Science and Youth Today, among others. Donavyn was a Fulbright Fellow to Denmark where she studied molecular nutrition and food policy. She holds a bachelor's degree in biotechnology from the University of Kentucky and master's degrees in food technology from Aarhus University and journalism from New York University.