In recent years, patients have become more and more interested in the aesthetic results of dental therapy, as the demands of white teeth by the society seem to be continuously growing. For this reason, teeth whitening has become one of the most wanted aesthetic procedures in dentistry. The performance of the procedure as well as the chemistry of the reactions that take place are well researched and scientifically corroborated, and are in favor of the security of the procedure itself. The bleaching materials contain one of the hydrogen peroxide derivatives (hydrogen peroxide, carbamide peroxide or sodium perborate) as an active bleaching agent. The basic mechanism of the reaction of hydrogen peroxide has not been fully clarified, but it is considered that the oxidation process, where the large pigmented molecules dissolve into less ones, is responsible for whitening. With the increased popularity of various types of whitening techniques and the accompanying development of countless commercially available products, the focus of more research has also been found to evaluate whitening errors mainly related to the effect of a bleaching agent on the oral tissue. The most common mistakes that occur at the time are postoperative hypersensitivity and gingival irritations, which are usually mild, moderate and transient. A possible mistake in avital bleaching is an external root resorption, although it is also successfully preventable. No permanent changes in hard dental tissues have been recorded. Moreover, there is no evidence to suggest a toxic or carcinogenic risk of hydrogen peroxide if the procedure is properly performed. Not all patients are candidates for the whitening process, so it is essential to make a thorough examination and to establish the existence of indications and contraindications for whitening.