If you're using Crest Whitening strips, the makers use a strong form of bleach, to help whiten your teeth. If you leave the strips on too long, the bleach may start to burn the nerves in your gums. It's not like the nerves BURN AWAY... but it will cause quite a bit of discomfort and/or pain in your gums. Your teeth might also feel extremely sticky if you leave it on too long. Additionally, if you leave them on overnight by mistake, your teeth will be really sensitive for a couple of hours. Not to mention, Crest Whitening Strips are ultimately less effective after the time span is up. In the end, leaving them on for a long time is doing you no good, what-so-ever.
I do not recommend leaving them on after the recommended time.
