These strips do whiten my teeth a shade or two after a few uses. I never use the whole box consecutively because they make my teeth more sensitive. I usually use them every other day for a week to 10 days and then stop. They aren't too uncomfortable to wear, but if some of the gel gets on my gums it will sting. The effects don't last as long as I'd like them to. I don't smoke or chew, but the stains on my teeth seem to come back within a couple of weeks. The results may be different if I would finish out the whole box.