Carbamide peroxide breaks down into urea and hydrogen peroxide. Hydrogen peroxide is the active ingredient in both. Carbamide peroxide breaks down to about one third hydrogen peroxide, so an 18% carbamide peroxide solution has the same effect as a 6% hydrogen peroxide solution. The reason carbamide peroxide is more common is because it is much more stable than hydrogen peroxide, which deteriorates rapidly in store/dentist shelves.
