Hydrogen Peroxide is the main active ingredient of Carbamide Peroxide. The ingredients list has only the very basic elements, one of them being hydrogen peroxide. Hydrogen peroxide is combined with other elements and becomes Carbamide Peroxide.
The amount of hydrogen peroxide used and the way it is combines determines the % off the carbamide peroxide.
In summary:
Carbamide peroxide contains hydrogen peroxide at a ratio of 1:3. For example, a product with 44% carbamide peroxide has about 15% hydrogen peroxide.