Extrinsic stains are those that only affect the surface of the teeth and can be removed by prophylaxis. Mostly these arise from the interaction of pigments from food and beverages with the plaque covering the enamel. This can easily be removed by dental prophylaxis and polishing. When this type of staining penetrates the microscopic cracks and fissures of the teeth, they cannot be removed by tooth-brushing or dental prophylaxis. In these instances, chemical whitening is required.

The key difference between hydrogen peroxide and carbamide peroxide is their breakdown rate and oxygen ion release. Carbamide peroxide is more stable and breaks down slowly, with about 50% of its peroxide releasing in the first 2 to 4 hours, and the rest over the next 2 to 6 hours. In contrast, hydrogen peroxide breaks down quickly, releasing all its peroxides within the first hour. This concentrated peroxide exposure in hydrogen peroxide is believed to cause more sensitivity compared to carbamide peroxide at similar concentrations.