Multiple side effects related to bleaching were found to occur in the dental pulp tissue, including decreased cell metabolism and viability. In this work we evaluated the in vitro diffusion capacity, cytotoxicity and biocompatibility of four commercial bleaching products on stem cells from human dental pulp (hDPSCs). Two commercial bleaching gels hydrogen peroxide-based (HP), Norblanc Office 37.5% (Nor-HP) and Opalescence Boost 40% (Opal-HP) were applied for 30 min to enamel/dentine discs. Another two gels from the same manufacturers, 16% carbamide peroxide-based (CP), Norblanc Home (Nor-CP) and Opalescence CP 16% (Opal-CP), were applied for 90 min. The diffusion of HP was analysed by fluorometry. Cytotoxicity was determined using the MTT assays, the determination of apoptosis, immunofluorescence assays and intracellular reactive oxygen species (ROS) level. Tissue inflammatory reactions were evaluated histopathologically in rats. Statistical differences were performed by one-way ANOVA and Bonferroni post-test (α < 0.05). Normon products showed lower cytotoxicity and diffusion capacity than the Ultradent products. A high intracellular ROS level was measured in hDPSCs after exposure to Opal-HP. Finally, a severe necrosis of both coronal and radicular pulp was observed with Opal-HP. Similar concentrations of hydrogen peroxide and carbamide peroxide in a variety of bleaching products exhibited different responses in cells and dental pulp tissue, suggesting that bleaching products contain unknown agents that could influence their toxicity.