You apply the plastic of the tooth whitening strip to your teeth, where it wraps around to fit their shape. The design and texture ensure that it does not slip or fall. There is a gel at the back of the strip that makes contact with your teeth directly.
This is what breaks up the marks and stains. You wear the strips once a day, for about 30 minutes at a time, during which you can carry on with your normal daily activities, including talking and drinking water. You should see noticeable results within a few days, but a full course of treatment generally takes two to three weeks.
Traditionally, teeth whitening strips use hydrogen peroxide for the gel, which is a powerful bleaching agent. However, this is not suitable for people with sensitive teeth, and there are alternatives, such as lemon peel oil.
Other common ingredients include PVP as a thickening agent and soothing, calming oils such as those from mint or coconut (which can also improve taste).