"When used following manufacturer’s instructions, hydrogen peroxide and carbamide peroxide based tooth whitening is safe and effective. However as with all dental therapies, there are risks, and practices should be tailored to the needs of each individual patient, based upon type and extent of staining, dietary habits, previous restorations and other intraoral conditions.  Patients should be informed of the risks associated with tooth whitening and, if using agents at home, instructed for identification of adverse occurrences in order to seek professional help if needed. Supervision of the tooth whitening strategy by an oral health care professional will reduce the potential risks and optimize benefits of tooth bleaching."
-Li Y, Greenwall L. Safety issues of tooth whitening using peroxide-based materials. Br Dent J 2013;215:29-34.

Source
Carey, C. (2014).  Tooth Whitening:  What We Know, Journal of Evidence-Based Dental Practice Special Issue, Vol. 14.,