Image used for representation.
London, Charcoal-based toothpastes, which claim to whiten teeth, are a "marketing gimmick" which could increase the risk of tooth decay and staining, says a review in the British Dental Journal.
The charcoal products, which are increasingly popular, often contain no fluoride to help protect the teeth.
Dr Joseph Greenwall-Cohen, co-author of the study from the University of Manchester Dental School, said "more and more shops are selling charcoal-based toothpastes and powders", including Superdrug, Boots and Tesco, after celebrities had started talking about using them.
But he said the claims they made had been found to be unproven by a 2017 US review of 50 products.
He said charcoal toothpastes and powders were more abrasive than regular toothpastes, potentially posing a risk to the enamel and gums. The charcoal contained in today's toothpastes is usually a fine powder form of treated charcoal, the review said.
"When used too often in people with fillings, it can get into them and become difficult to get out," Dr Greenwall-Cohen said.
Prof Damien Walmsley, from the British Dental Association, said: "Charcoal-based toothpastes offer no silver bullets for anyone seeking a perfect smile, and come with real risks attached. "So don't believe the hype. Anyone concerned about staining or discoloured teeth that can't be shifted by a change in diet, or improvements to their oral hygiene, should see their dentist."
Charcoal can be made from materials including nutshells, coconut husks, bamboo and peat, and possibly wood and coal.
Charcoal was first used for oral hygiene purposes in ancient Greece, as a way of removing stains from teeth and disguising unpleasant odours from diseased gums.
