Do whitening strips expire?

Whitening strips: Yes the whitening agent in most stips or tubes will expire. After so long it will degrade to water and no longer be effective.

Yes: The expiration date should be listed on the package. Using it after the expiration can't hurt the teeth or gums, it merely will not be (as) effective.

Yes : Since the active ingredient is a peroxide and peroxides are unstable by nature they will loose effectiveness over time. If you want to increase the shelf life you can refrigerate them.

Yes: Yes, look on the label, keeping whitening products possibly in refrigerator can extend their life.