Best for: People with mild staining and plenty of tooth enamel. "Don't use these kits if you grind your teeth, have recessed gums, or think you might have a cavity, because the peroxide has a propensity to seep into sensitive areas caused by recession or grinding," says Michael Apa, DDS, founder of New York University's Aesthetics Dental Society.
Do they work? Not as well as in-office bleaching. Drugstore whitening kits simply aren't able to achieve the kind of bleaching you can get in the dentist's office or with trays, says Robert Reiss, DDS, who has a private practice in New York City. At-home kits will lighten teeth, but you have to be committed and patient; it can take several weeks or more of daily applications to see results, and your teeth may become temporarily sensitive in the process. A common complaint is that the strips are either too narrow and short to fit large teeth, so they don't bleach evenly, or they're so big that they irritate the gums, says Lieb.