Teeth turn yellow because of exposure to materials that cause extrinsic and intrinsic stains. Extrinsic stains occur on the surface of a tooth, while intrinsic stains occur inside the tooth. Most extrinsic stains occur on the enamel and are caused by foods in one's diet. Intrinsic stains, which change the light-transmitting properties of the enamel, are often caused by drugs and other medications.
Foods and drinks that are dark are more likely to cause teeth to appear yellow. This means that fruits such as grapes, pomegranates and blueberries have a higher potential of staining teeth than do lighter fruits. Drinks such as coffee and cola have a similar effect. All these foods and drinks are high in chromogens, which produce pigments that often adhere to tooth enamel. Chewing tobacco and smoking also increase the likelihood of yellow teeth due to plaque that collects on the teeth when these products are used.
Some of the medications that cause intrinsic stains include tetracycline and doxycycline (if children are younger than 8) and minocycline, which is an acne-treating drug. In addition to extrinsic and intrinsic staining, aging also can cause teeth to yellow. Likewise, some people's teeth simply appear more yellow because of genetics.