With whitening strips, there are ingredients such as peroxide to help whiten your teeth. Peroxide is a type of bleach that can remove the stains on your teeth and reduce the concentration of possible stains to make your teeth appear whiter. The strips are made of a thin layer of plastic covered with peroxide gel. Depending on the brand of whitening strips you are using, you are most likely to wear the strip for at least 30 minutes (once or twice) a day for two weeks.