Can teeth whitening strips expire?

Yes: Yes, you can expect them to be less effective as time goes on. For the best results use fresh ones.

Yes: The active ingredient will degrade or weaken over time and it will not be as powerful. Look at the expiration label on the box. They will. To work well if expired.

Yes: Tthere is an expiration date on the individual packets. The boxes of crest whitestrips does have such a date. They likely presume that users will keep the box on hand.