Those strips and gels you use to get your teeth as pearly white as possible may come with some previously unknown risks, according to new, preliminary research out this week. It found that the key ingredient in these products—hydrogen peroxide—could be capable of damaging dentin, the second, deeper layer of our teeth that lies beneath the enamel surface.

Though organizations such as the American Dental Association do warn whitening products can cause tooth sensitivity or gum inflammation, they’re seen as temporary side effects that go away soon after you stop using them. And by and large, these products are considered safe and effective.

Read more at Gizmodo.