Did You Know? These 10 Things Can Damage Your Teeth

Peroxide-based bleaching agents can cause increased sensitivity in your teeth, particularly early on in the bleaching process. Soft tissues, especially your gums, may become irritated.

While its occurrence is rare, damage that cannot be reversed has been reported even after cessation of the whitening treatment.

Source:

Statement on the Safety and Effectiveness of Tooth Whitening Products
http://www.ada.org/en/about-the-ada/ada-positions-policies-and-statements/tooth-whitening-safety-and-effectiveness