The expiration date for Crest Whitestrips can be found on the side of the original box purchased. If the box was discarded, it is not harmful to use the strips, but it is better to be aware of the date.
For best results for teeth whitening, always check the expiration date on the box in which the Crest Whitestrips are stored. If the strips have expired before they are used, the active ingredient that whitens the teeth is no longer active and is not effective for the strips' intended use. The Crest Whitestrips should be used according to the directions on the package.