What does teeth whitening strips do to make your teeth white?

I was just wondering if it was harmful to my teeth.
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The ingredient in the teeth whitening strips acts as a bleach to whiten the teeth. Take note that the strips can only whiten the areas that they can touch. So they are limited when it comes to reaching between teeth and in any cracks in the teeth. If you know you have sensitive gum and teeth, you should check with your dentist if you are suitable to use the teeth whitening strips. This is because these teeth whitening strips can cause irritation to the gums.
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