One paper published in 2019 found that charcoal toothpaste can whiten teeth within 4 weeks of use, but it wasn't as effective as other whitening toothpastes. Research has found that activated charcoal can be abrasive on teeth and tooth-colored restorations, leading to loss of tooth structure.

Is charcoal teeth whitening bad for your teeth?

The main danger with using charcoal to whiten your teeth is that it's a very abrasive substance. The grittiness it provides does remove surface stains and plaque from your teeth, but it's so harsh that it also wears away the top layer of the tooth, called the enamel.

Is it OK to brush your teeth with activated charcoal?

Disregarding activated charcoal's abrasive nature, it's not bad for your teeth, per se, but if you're brushing with it, it's likely that it won't do much good for you in the long term, as it doesn't have enough time to sit on the surface of your teeth and produce any meaningful whitening effect.