Fig 2. Risk of bias assessment.

+ indicates a low risk of bias, -/+ indicates moderate risk of bias,—indicates high risk of bias,? indicates unknown risk, NA indicates bias is not applicable to the study. ^a Other sources of bias include whether confounders were appropriately accounted for and whether lactic acid-containing product details were sufficiently described in the manuscript. ^b One study disclosed receipt of funding from the lactic acid-containing product manufacturer. ^c Single arm prospective cohort study.