Hydrogen peroxide. A low-dose version of hydrogen peroxide has a known whitening effect on teeth and is the active ingredient in most whitening systems used in dentists' offices. While the concentration in whitening toothpastes is less than the amount in single-use products, hydrogen peroxide can produce excellent results (and is safe to use) over a longer period. The ADA notes that bleaching agents, such as hydrogen peroxide, can cause mild sensitivity but are still safe and approved for regular use.