I didn't believe other reviewers who said this mouthwash stained your teeth. But as I used it over several weeks, I noticed that the areas between teeth got a darker and darker. At first I thought it was my tea drinking. However, after I stopped using this mouthwash, the stains noticeably got better. Too bad, I quite like the taste of the Crest mouthwashes. Back to good old Listerine for me!