Teeth whitening strips contain peroxide or bleach. Thus, they work to whiten your teeth the same way bleach works to whiten your clothes or your hair. The peroxide bleaches color from your teeth in order to restore their natural, white color.
Most whitening strips are made out of polyethylene, which is a thin, elastic type of plastic. The plastic is coated with peroxide, and certain types of strips contain more than others. You apply the strips to your teeth according to the package directions so that the peroxide comes into contact with your . This allows the peroxide to remove stains and discoloration from the surface of your teeth. Some strips need to be removed after a certain period of time, while others do not.