Charcoal toothpastes and powders are sold on a straightforward visual promise. The difficulty is that the properties determining whether they work, or cause harm, are seldom disclosed in comparable terms.
Two different mechanisms are being claimed at once
Activated charcoal is porous and binds certain molecules to its surface, a process called adsorption. That property is the basis of most marketing claims.
Separately, a charcoal particle in a paste acts as an abrasive, physically removing surface film through mechanical action during brushing.
These are unrelated mechanisms, and a visible change after brushing does not indicate which one produced it.
Abrasivity is the property that matters most and is rarely stated
Toothpaste abrasivity is measured on a standardized relative scale, and the value depends on particle hardness, size and shape rather than on the ingredient's name.
Manufacturers are not generally required to print that value on the package, so buyers cannot compare products on the specification most relevant to enamel wear.
Particle characteristics also vary between production sources for the same nominal ingredient, so the category name does not predict the number.
Fluoride content and stability complicate matters
Many charcoal formulations are marketed as fluoride-free, which removes the component with the strongest evidence base for decay prevention.
Where fluoride is included, questions arise about whether an adsorbent material affects its availability in the formulation, and that is a formulation-specific matter.
Neither point can be assessed from the front of a package, and ingredient lists give order rather than quantity or availability.
Surface removal is not the same as whitening
Removing surface film can reveal the tooth's underlying color, which looks like whitening but changes nothing inside the tooth.
Peroxide-based products act on pigment within the tooth structure, a different chemical process with a different ceiling on what it can achieve.
Products relying on surface removal therefore reach a limit quickly, and continued use is not doing what continued use of a peroxide product does.
What a buyer can reasonably check
Useful questions are whether the product contains fluoride, whether abrasivity information is published anywhere by the manufacturer, and what claim if any has been independently evaluated.
Existing restorations, exposed root surfaces and thin enamel change the calculation, because abrasion affects those surfaces differently than intact enamel.
Anyone with sensitivity, recession or visible wear should ask a dentist before adopting an abrasive product, since the risks are individual rather than general.