The outer layer of a tooth is called the enamel. The color of natural teeth is created by the reflection and scattering of light off the enamel, combined with the color of the dentin under it. Your genes affect the thickness and smoothness of the enamel. Thinner enamel allows more of the color of the dentin to show through. Having smoother or rougher enamel also affects the reflection of light and therefore the color.

Every day, a thin coating forms on the enamel and picks up stains. Tooth enamel also contains pores that can hold stains.

The most common reasons for teeth to get yellow or stained are:

  • Using tobacco
  • Drinking dark-colored liquids such as coffee, cola, tea and red wine
  • Not taking good care of your teeth

Aging also makes teeth less bright as the enamel gets thinner and the dentin becomes darker.

It is also possible to have stains inside the tooth. These are called intrinsic stains. For example, intrinsic stains can be caused by exposure to too much fluoride as a child while teeth are developing. Other causes include tetracycline antibiotics. They can stain a child’s teeth if taken by a mother during the second half of pregnancy or by a child who is 8 years old or younger. Teeth are still developing during these years. Trauma may also darken a tooth.

Tooth whitening is most effective on surface (extrinsic) stains.