The precise reason that whitening causes sensitivity is not fully known, but the leading theory is that it’s due to “dentinal microtubules.” These extremely small, microscopic channels in our teeth connect the exterior of the tooth enamel to the interior nerve, allowing us to feel sensations in our teeth.The theory is that, since peroxide-based whiteners weaken the enamel very slightly, this exposes the microtubules, which become much more sensitive. Then, as the enamel remineralizes and becomes stronger after the whitening process is over, they are sealed up again, and no longer feel overly sensitive. This would explain why the sensitivity caused by teeth whitening typically only lasts for a few days.