All of our products are designed to be gentle on teeth. Smirk Powder contains ingredients that actually calm the nerves and form a barrier over microscopic holes in your enamel, helping with sensitivity. Most users won’t experience discomfort or sensitivity with our Teeth Whitening Strips either, since they are peroxide-free. Discontinue use or consult your dentist if you do experience sensitivity with Smirk strips. All of that being said, if you have bleeding or receding gums, or damaged teeth, please see a dentist before use (they don’t bite!)