"Home bleaching" methods are commonly used in dentistry to correct tooth discoloration. This technique employs carbamide peroxide, in several concentrations, where the active component is hydrogen peroxide. In patients undertaking this treatment, this exposure can cause biological effects mainly due to the activity of hydrogen peroxide. Hydrogen peroxide is associated with effects induced by chemical (natural and synthetic substances) and physical agents (ionizing radiations). We have evaluated the cytotoxic effects of four commercial dental bleaching agents: Insta-Brite, Karisma, Opalescence and Whiteness. We have studied the effects of these agents on the survival of different E. coli strains with various capabilities to repair damages on the deoxyribonucleic acid (DNA): AB1157 (wild type), AB2463 (recA) and BW9091 (xthA). To determine the effect of the bleaching agents on the survival of E. coli AB1157, AB2463 and BW9091, cultures in exponential growth-phase were incubated with the bleaching agent or with 0.9% NaCl, as a control. After plating, the survival fractions were determined. The bleaching agents tested decreased the survival fractions of all strains studied and the E. coli BW9091 was the most sensitive and, moreover, these bleaching agents are capable of inducing damage to the DNA molecule. In conclusion, our results indicate that dental bleaching agents can generate biological effects like the ionizing radiations, and we suggest that dental professionals involved in bleaching to correct tooth discoloration, should control the clinical environment strictly, thus preventing contact between the oral mucosa/gingival tissues and the bleaching agents.