There are numerous types of teeth stains; some are genetic, environmental or pharmacological in nature. The most common are surface stains on the enamel or beneath the enamel in the dentin. Surface stains are caused by foods, beverages and lifestyle behaviors, like smoking. Over time, surface stains may penetrate the enamel and change the color of the dentin, which darkens the overall appearance of the tooth due to the translucency of the enamel layer. When this occurs, the tooth often appears yellow.