BACKGROUND In most hair restoration practices, hydrogen peroxide has been routinely used to remove blood during and after hair transplant surgery. In other specialties, hydrogen peroxide is also used in these ways: wound cleaning, prevention of infection, hemostasis, and removal of debris. Despite its widespread use, there are still concerns and controversy about the potential toxic effect of hydrogen peroxide. OBJECTIVE The objective was to review all available literature including in vivo and in vitro effects of hydrogen peroxide, as well as general wound healing research. MATERIAL AND METHODS Literature up to and including the past three decades was investigated. RESULTS Two pilot studies were found, and there are not enough data examining the real impact of using hydrogen peroxide in hair transplant surgery. In other specialties, H2O2 appears to have positive effects, such as stimulation of vascular endothelial growth factor, induction of fibroblast proliferation, and collagen, or negative effects, such as cytotoxicity, inhibition of keratinocyte migration, disruption of scarless fetal wound repair, and apoptosis. CONCLUSIONS There are not enough data in hair restoration surgery about the use of hydrogen peroxide, and it is unknown and unclear what the optimum dilution should be. Positive and negative effects were found in other specialties. Further studies are recommended.