Normally post-whitening sensitivity is worst the first few hours after the procedure and should gradually subside in 12 hours or less. If it persists beyond that, there is likely gum recession and exposed roots of some of the teeth which makes them much more sensitive. However if that is the case, the sensitivity should go away within a few days. Patients in our office who have a history of sensitivity prior to whitening are often instructed to use a high strength topical fluoride for several days prior to and after the procedure to reduce or avoid sensitivity. It is very important to follow the instructions of your dentist when using a take-home product or the manufacturer’s instructions on the over the counter products. When used properly, tooth whitening products do a great job. When used to excess, they have the potential to damage your teeth or make them very sensitive. Good luck.