Cold light is actually a catalyst, the real whitening effect is still the whitening agent, the most commonly used whitening agent composition is 35% hydrogen peroxide, apply this hydrogen peroxide material evenly on the tooth surface and then cold light irradiation, the hydrogen peroxide will react with some pigments on the tooth surface, after that the small molecule material will be deliquesced, thus whitening effect. The risk of teeth whitening by cold light is very small, but any whitening operation may have risks, such as tooth sensitivity, tooth abrasion, hidden cracks and chipping. During the process of cold light whitening treatment, there is a possibility of tooth soreness. Those with mild symptoms can be treated without much treatment, while more serious cases can be treated with oral painkillers. Patients with the above mentioned problems need to inform the physician in advance before doing the cold light whitening treatment. In addition to tooth soreness, mouth, mucous membrane and gum burns may occur. During the treatment, the practitioner will try to avoid this series of problems. If these problems do occur, they will be restored to health quickly with professional treatment. If there are restored teeth such as fillings, dentures, porcelain teeth, veneers, etc., they cannot be changed during the cold light treatment. Patients with such teeth should inform their physicians in advance to avoid color differences with their natural teeth after whitening.