There are certain health trends that do more harm than good, from exfoliating the vagina and staring into the Sun to eating your own placenta. 

Now, you can add charcoal toothpaste to the list.

Activated charcoal, as a health trend, started to pick up steam in 2016. Today you can find it in everything from black lattes to goth ice cream. Even pizza, burger buns, and French pastry sometimes include it.

There is no doubt that part of its appeal lies in its Instagram aesthetic. (See also: ube, unicorn toast, and many of today’s top food trends.) But its popularity also comes down to various health "benefits" attributed to charcoal. In particular, those that class it as a "detoxifier". 

According to a review recently published in the British Dental Journal, demand for charcoal toothpaste seems to be increasing in many countries. The US, UK, and Australia included.

Purchasers of charcoal toothpaste might do so because of claims it whitens teeth and removes impurities by binding to all tooth surface deposits. However, the researchers say it is no more than "a fashionable, marketing ‘gimmick’". Worse than that, activated charcoal can actually cause tooth decay and staining. Two things you really don't want from your toothpaste.

The researchers point to a 2017 literature review that analyzed the findings of 118 articles and featured a database of 50 charcoal-based toothpastes. It found "insufficient scientific evidence to substantiate the cosmetic, health benefits (antibacterial, antifungal, or antiviral; reduced caries; tooth whitening; oral detoxification), or safety claims of marketed charcoal-based dentifrices." 

These cosmetic and health benefits include tooth-whitening capabilities (claimed by 96 percent of products), capacity for detoxification (46 percent), antibacterial or antiseptic (44 percent), remineralization, strengthening, or fortification of the teeth (30 percent), low abrasivity (28 percent), and antifungal (12 percent).

"This ‘scientifically claimed until proved wrong’ approach is favored over substantiated, evidence-based promotion," the authors write. 

Another major problem with many of the toothpastes analyzed, the authors note, was their distinct lack of fluoride. Fluoride can be toxic in the wrong doses but the low levels found in most common toothpaste products are a key ingredient, preventing tooth decay and remineralizing teeth to make them stronger.

Just 8 percent of the toothpastes analyzed contained fluoride. What's more, any benefit fluoride has in those 8 percent of products could be null and void due to the presence of activated charcoal, which has an extremely high absorptive capacity. This means it could "inactivate" the chemical.

Another issue is the level of abrasivity found in these products. It is often much higher than those of regular toothpastes and, therefore, when used regularly, could damage the enamel and gums, the researchers say.

While there is a renewed interest in charcoal toothpaste of late, charcoal has been used as an oral hygiene product at least since the time of the ancient Greeks and there are records of its use in many other parts of the world as well.

Still, the study authors advise, if you want to keep your pearly whites in tip-top condition, it is best to stick to your standard fluoride-based toothpaste and speak to your dentist about any additional bleaching and whitening options.