Activated charcoal toothpaste doesn't whiten teeth as well as other options—some studies found no significant whitening effect at all. The bigger concern: it's significantly more abrasive than alternatives, which means it can wear down tooth enamel with regular use.

Researchers reviewed 11 peer-reviewed studies (out of 208 initial results) that tested activated charcoal toothpaste on real teeth or extracted teeth to measure both whitening power and abrasiveness.

Funding not disclosed in abstract