Whitening strips are thin, flexible plastic strips coated with a whitening gel that contains hydrogen peroxide or carbamide peroxide. They are designed to be applied directly to the teeth for a specified period, usually ranging from 30 minutes to a few hours, depending on the product. These strips work by penetrating the enamel to break down stains and discoloration, resulting in a brighter smile. Most whitening strips are available over-the-counter and come in various strengths and formulations. Users typically see results within a few days to weeks, depending on the frequency of use and the severity of the stains. It's important to follow the instructions carefully to avoid potential side effects, such as tooth sensitivity or gum irritation.