The implausible "in vivo" role of hydrogen peroxide as an antimicrobial factor produced by vaginal microbiota

In the cervicovaginal environment, the production of hydrogen peroxide (H₂O₂) by vaginal Lactobacillus spp. is often mentioned as a critical factor to the in vivo vaginal microbiota antimicrobial properties. We present several lines of evidence that support the implausibility of H₂O₂ as an "in vivo" contributor to the cervicovaginal milieu antimicrobial properties. An alternative explanation is proposed, supported by previous reports ascribing protective and antimicrobial properties to other factors produced by Lactobacillus spp. capable of generating H₂O₂. Under this proposal, lactic acid rather than H₂O₂ plays an important role in the antimicrobial properties of protective vaginal Lactobacillus spp. We hope this commentary will help future research focus on more plausible mechanisms by which vaginal Lactobacillus spp. exert their antimicrobial and beneficial properties, and which have in vivo and translational relevance.