Most stains fall into two categories: extrinsic and intrinsic stains. Extrinsic stains, which are the most common kind of tooth stain, come from the intake of coffee, soda, wines and even some foods. Tobacco can also cause extrinsic stains. These stains are all on the surface of your teeth and are easier to remove with whitening treatments. Intrinsic stains appear when the dentin, the inner substance of your tooth, changes to a darker or more yellow shade. Exposure to too much fluoride as a child when your permanent teeth begin to erupt or even dental trauma can affect the already yellow-hued dentin inside your teeth. Occasionally, medications can change the color of dentin, such as chemotherapy or radiation treatments. Thinning enamel is another factor to consider when determining what sort of stains your teeth may be facing. While technically not a stain, as the enamel thins, more of the yellowish dentin beneath shows through. It’s completely natural to see this sort of change as you get older, but it can be helped with whitening treatments.