However, some fashionable ingredients should be treated with caution. Charcoal, which has been used to clean teeth for millennia and has become increasingly popular in commercial toothpastes, has less research to back it up. There is little evidence charcoal whitens teeth, and it may increase the risk of tooth erosion and other problems. Claims regarding antibacterial, antifungal and antiviral properties of charcoal toothpastes cannot be substantiated, according to one review, concluding dentists should "advise their patients to be cautious when using charcoal and charcoal-based [dental products] with unproven claims of efficacy and safety".