Carbamide peroxide, also known as urea peroxide, is a form of hydrogen peroxide that is made more stable by reacting it with urea. If you don’t yet know the difference between carbamide peroxide (CP) and hydrogen peroxide (HP) bleaching gels, click HERE. Compared to hydrogen peroxide (HP) gel, the most important aspects of carbamide peroxide teeth whitening gel is that: It has a longer shelf-life, It does not require refrigeration It is slower acting and therefore less aggressive on soft tissues such as lips and gums. Whereas these features make carbamide peroxide the best gel for home teeth whitening products, it is also appropriate for use in chair-side (in-office) applications that use a mouth tray. We never put hydrogen peroxide in a mouth tray because a strong hydrogen peroxide gel in a tray will cause significant gum irritation. Treatments with carbamide peroxide gel need to be longer (at least 20 minutes per application) because it takes at least 10 minutes for the urea peroxide just to start breaking down into hydrogen peroxide, which is necessary before it starts whitening. For faster in-office whitening treatments, we recommend kits with hydrogen peroxide gel.