It hurts the gum a lot!
I bought this product for my husband but he only used for one week and refused to continue because the innerside gel make his gum hurt. Later I tried myself for a few days. For the first day, it's okay. But for the following days, it really hurt my upper gum so I stopped. We both used a few days, nonetheless we noticed a little whiter upper teeth. I guess it will whiten your teeth but if you have sensitive gum you better have the stamina to finish.
Rating: 3 stars