Yes, all bleach or whitening does, but they are very careful not to use too much so chances are you won't have any problems at all. Unless you have it done a million times.
The bleach that is used for whitening teeth is actually quite safe for tooth enamel, but it can cause irritation on the gums if used improperly or too often.
kai ^_^ i wasn't sure if it could mess up the enamel on teeth.
