Review (2/5): I've used this product several times, once a week ...
I've used this product several times, once a week. After using it twice over two weeks, I noticed my lips cracking, especially at the corners. Over the course of one week, my lips starting going numb. I didn't know why, so I laid off of the product for two weeks. The numbness slowly went away after another week, so I thought I'd give the whitening another go. Mistake. My lips immediately started taking their course of cracking and going numb again.
I did notice a difference in the whitening, but not worth numb lips and my body's reaction to it. I'm done with this product.