While it is true that teeth whitening by bleaching does work, it does not come without side effects. There are many reported incidents of increased tooth sensitivity after bleaching. Prolonged exposure to bleaching agents can damage tooth enamel. If the treatment is not administered properly, there can be complications like gum irritation. The oxidizing agents are very strong and can damage the soft tissues of your mouth. The bleaching effect can also cause irritation and increased sensitivity to cold and hot fluids and sometimes even to air. In the case of home bleaching, there is a chance that patients might ingest some of the bleaching gel. In such a case, the person might experience burning or nausea.
According to a Brazilian study done in 2004, increased sensitivity is an inherent characteristic of the bleaching process - and is commonly experienced. During bleaching with carbamide peroxide, the bleaching agent can actually expose microscopic particles of the inner tooth, known as dentin. If cold water is ingested or reaches the dentin, it can cause a slight contraction that's felt as increased sensitivity. The heightened sensitivity will continue until the temperature of the tooth warms back to body temperature.
In detail, the photomicrograph above shows various photos of tooth enamel taken during a whitening treatment using carbamide bleaching agents. A greater degree of porosity (enamel prism dissolution) occurs as the bleaching time is increased. The complete dissolution of the enamel rod prism could account for sensitivity to cold water after bleaching.
When receiving professional teeth whitening, minimal sensitivity and good whitening results rely on factors such as pH, viscosity, and stability and, most importantly, the rate at which the carbamide breaks down into hydrogen peroxide and then oxygen. Many manufacturers have chosen carbamide, as it is more stable than hydrogen peroxide. However, this also causes a slower release of the oxidizing agent and necessitates longer procedures. Some manufacturers have tried to accelerate this by adding heat (in the form of light). This can have a minimal effect but it can also be a major cause of extreme sensitivity.
We have written an in-depth article on possible teeth whitening dangers located in the article section.