Glycolic acid chemical peeling improves inflammatory acne eruptions through its inhibitory and bactericidal effects on Propionibacterium acnes

Abstract Glycolic acid chemical peeling is effective for treating comedones, and some clinical data show that it also improves inflammatory eruptions. The purpose of this study was to identify the mechanism of glycolic acid chemical peeling to improve inflammatory acne. To assess growth inhibitory and bactericidal effects of glycolic acid on Propionibacterium acnes in vitro , we used an agar diffusion method and a time‐kill method. To reveal bactericidal effects in vivo , we established an agar‐attached method which correlated well with the ordinary swab‐wash method, and we used the agar‐attached method to compare the numbers of propionibacteria on the cheek treated with glycolic acid chemical peeling. Our results show that 30% glycolic acid (at pH 1.5, 3.5 and 5.5) formed growth inhibitory circles in the agar diffusion method, but the diameters of those circles were smaller than with 1% nadifloxacin lotion or 1% clindamycin gel. In the time‐kill method, 30% glycolic acid (at pH 1.5 and 3.5) or 1% nadifloxacin lotion reduced the number of P. acnes to less than 100 CFU/mL within 5 min. In contrast, in 30% glycolic acid (at pH 5.5) or in 1% clindamycin gel, P. acnes survived for more than 4 h. Chemical peeling with 35% glycolic acid (at pH 1.2) decreased the number of propionibacteria on the cheeks of patients compared with untreated controls ( P  < 0.01). Our results demonstrate that glycolic acid has moderate growth inhibitory and bactericidal effects on P. acnes , and that chemical peeling with glycolic acid works on inflammatory acne via those effects.