Black charcoal-based toothpaste that promises to whiten teeth is a "marketing gimmick", according to a review in the British Dental Journal.
Made popular after bloggers and social media personalities were seen using them, the often products contained no fluoride, which is essential in fighting tooth decay.
In fact, excessive brushing with them can increase the risk of abrasions, advance tooth decay, all while not actually whitening your teeth, the report found.
It studied 50 different kinds of charcoal toothpaste and found only 8% contained fluoride.
As many as 96% of the products claimed to have tooth-whitening properties, however, they did not contain enough free radical bleaching agent for this purpose.
It also highlighted several possible health risks that charcoal-based toothpaste may induce due to the potential presence of carcinogenic polyaromatic hydrocarbon.
The popularity of the products is increasing in many European countries, according to the document, including the UK, Lithuania, and Switzerland, where charcoal-based toothpaste have been reported to be produced.
The review's authors said patients should see their dentist if they were considering whitening their teeth.
The use of charcoal for oral hygiene purposes can be traced back to ancient Greece when it was used to get rid of staining and odours from diseased gums.