Why teeth turn yellow?

There are two types of whitening because there are two main ways that teeth turn yellow.
For everyone, teeth yellowing is a normal part of aging. Our hair turns gray and our teeth turn yellow. It’s the inner part of the tooth called dentin—not the outer enamel—that yellows. As teeth repair themselves, the new dentin is darker, and the enamel is getting thinner due to wear, and things like grinding your teeth or acids from foods you eat can thin enamel earlier, making teeth become yellow sooner. The color of dentin reflects through enamel like a prism, making the tooth look yellow.

Besides aging, teeth turn yellow or gray due to:

  • Taking tetracycline before age 10
  • Falling on or hitting a tooth
  • Too much fluoride (also called fluorosis)
  • A rare dental disorder called Amelogenesis Imperfecta (AI) which makes the teeth yellow or brown
  • Genetics, which determine the color of your teeth to begin with
  • Silver fillings
The outer part of the tooth – enamel – can also get stained when you drink tea, coffee, wine, or smoke tobacco. This is called staining and it does not affect the inner colour of the teeth.

How whitening works?


“Intrinsic” refers to whitening the inner part of the tooth, which soaks up hydrogen peroxide gel (also called whitening gel or bleach) and becomes lighter.

When the inner part of the tooth is whitened, the colour that’s reflected through the outer enamel of your teeth is lighter, making them look whiter and brighter—reflecting out through the enamel like a prism.

Contrary to what you might have thought, bleach lightens the inner tissue of the tooth, not the hard, outer enamel.


Removing staining on enamel (the outer part of the tooth) is called extrinsic whitening. The stains left behind by smoking, wine, tea, and coffee are usually easily removed with a polish by your hygienist at a teeth cleaning or with polishing and whitening toothpaste, which we’ll discuss in a bit.

Which kind is right for me?

It depends on whether your teeth are intrinsically yellow or if you’re just dealing with staining.

If you have extrinsic discoloration (i.e. staining from things like coffee and tea) it can be removed by cleaning the teeth with a professional teeth cleaning. Bleach will not work well on extrinsic discolouration.

If you have intrinsic yellowing, no amount of stain-removing toothpaste can lighten the intrinsic colour of the tooth. You’ll need to whiten your teeth using a bleaching gel that is held up against the teeth.

What to know before you start?

Here’s what to know before you begin:

Start with healthy teeth

You can’t remodel the kitchen if there’s dry rot in the floor boards. Whitening your teeth when you have gum disease, exposed roots, cavities, crooked teeth, gum recession, or other untreated issues can cause further pain and problems, plus you’ll have wasted your time, since the whitening likely won’t take on damaged teeth. An ethical dentist will tell you this and not take your money before fixing problems first.

It doesn’t last forever

Teeth are always yellowing as part of the aging process. They’re also always becoming stained by the foods and drinks we consume. No matter where or how you whiten your teeth, it won’t last forever. Most results last from 2 years to 3 years, but it all depends on how easily your teeth stain as well as your diet.

Results vary

The results you get depend on what your teeth were like when you started. Some people think whitening erases all the damage they’ve done to their teeth over their lifetimes. The opposite is true — the better you’ve cared for your teeth, the greater the results. If you have kept up on your dental appointments, brushed and flossed regularly, and avoided damage and discoloration, the whiter your teeth will appear after treatment.

Whitening is safe when done as recommended

Whitening is for the most part safe if done correctly by dentist.

Professional whitening at the dentist’s office

You’ll come into the office for a few sessions for about an hour each time. A high concentration of peroxide is applied to the teeth and a light is used, which supposedly accelerates the chemical reaction and the whitening.

If you need whitening fast for an upcoming event, this can be a good option. Theoretically, since the dentist is present, you reduce your risk of doing damage to your teeth.

When you may not want to whiten

If you fall into one of these groups, I recommend you talk with your dentist about your unique case, as whitening might not be right for you:

  • Your teeth are already very sensitive
  • You have GERD or acid erosion on your teeth
  • You have gum recession
  • Your gums are sensitive
  • You have sensitivity to hydrogen peroxide
  • You have white spot decalcifications (early cavity) which will become whiter and more noticeable after whitening
  • You are pregnant or breastfeeding
  • You have visible plastic fillings or crowns

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