Whitening systems use small bleach molecules that penetrate and diffuse into teeth. However, some whitening treatments can irritate the nerves of your teeth and leave them hypersensitive. Stimuli like temperatures and pressure can cause pulpitis on a tooth. Pulpitis means the pulp of your tooth is slightly irritated and inflamed. For whitening to work, the procedure often gets rid of a protein layer that opens up the “pores” of your teeth. This exposes the core of the tooth, or the dentin. While this is necessary for teeth whitening to work, it can cause sensitivity.