There are two types of tooth staining, extrinsic staining and intrinsic staining.
Extrinsic stains are those that appear on the surface of the teeth as a result of exposure to dark-colored beverages, foods and tobacco, and routine wear and tear. Superficial extrinsic stains are minor and can be removed with brushing and prophylactic dental cleaning. Stubborn extrinsic stains can be removed with more involved efforts, like teeth whitening. Persistent extrinsic stains can penetrate the dentin and become ingrained if they are not dealt with early. Intrinsic stains: Are those that form on the interior of teeth.
Intrinsic stains result from trauma, aging, exposure to minerals, chemicals and antibiotics like tetracycline during tooth formation and/or excessive ingestion of fluoride. These stains exist below the enamel and are unlikely to benefit from teeth whitening.