The good news: both are equally effective for tooth whitening. Hydrogen peroxide generally has a faster effect on stains, but it's not a great option for tooth whitening for sensitive teeth. As they break up stains, most hydrogen peroxide-based teeth whitening solutions also cause demineralization, making your teeth more porous. This exposes your dentinal tubules (vessels that lead to the nerves of your tooth), causing pain and sensitivity. This effect is experienced much more often by those using over-the-counter or in-office hydrogen peroxide solutions than those who use carbamide peroxide. Hydrogen peroxide attacks the stains quickly, but its strength can also cause more severe tooth sensitivity. Gentler carbamide peroxide formulas, such as foams, steadily expose teeth to the active oxygen molecules that break up persistent teeth stains. The difference in the rate of absorption helps to defend your teeth against excessive dentinal tubule exposure, reducing the chance of sensitivity from tooth whitening.