Your teeth can get stained from dark foods like beets and berries, drinks such as colas and tea, or substances in cigarette smoke. These can stick to plaque or tartar on your teeth and seep into the enamel. As you age, your enamel thins, exposing the yellowish dentin underneath. Professional whitening by a dentist is the most effective method, but at-home products can also work. Look for products with hydrogen or carbamide peroxide, which penetrate enamel and lighten stains. Strips and trays are the most effective, but they can make teeth more sensitive. If this happens, use the products every other day or switch to sensitive-formula toothpaste. Drugstore trays aren't customized to your bite and can irritate gums, but over-the-counter strips are better at placing peroxide on teeth. Whitening won't work on visible bonding or fillings, as they can't be lightened by peroxide. Whitening toothpastes have mild abrasives that remove superficial stains slowly. Mouthwashes with low levels of peroxide are better for fresh breath and don't provide significant whitening. Flossing cleans teeth well but doesn't significantly whiten them.