Ohio State University researchers tested five name-brand whitening products (strips and trays), all of which rely on hydrogen peroxide or carbamide peroxide to create free radicals that attack the pigment molecules in enamel, ultimately making teeth appear whiter when the molecules stop reflecting light. Their findings show that more than just the enamel's pigment molecules are affected by this process.
After what each brand defines as a full whitening treatment, the human tooth samples displayed enamel loss ranging from 1.2 to 2 nanometers. Additionally, when the the researchers tested their ability to bounce back, the teeth were up to 19% less capable.
Even though the loss of hardness is relatively minimal, it causes enough to concern for the justify changing these formulas, according the the researchers. They believe manufacturers may be able to alter concentrations and modes of application to make home tooth whitening safer.
In the meantime, if you continue using these products, you can help strengthen enamel by using fluoride toothpaste and other fluoride-based products.