Effects of common cosmetic ingredients on growth of dominant human skin inhabitant Cutibacterium acnes

Objectives

Cosmetic products, which typically contain multiple ingredients such as ethanol, glycerol and Tween 80 (polysorbate 80), may influence the homeostasis of the skin microbiome. However, the effect of common ingredients on the anaerobic members of human skin microbiome is poorly studied. In this study, we directly evaluated the effects of common cosmetic ingredients on a dominant human skin anaerobe Cutibacterium acnes using in vitro techniques.

Materials and methods

Five cosmetic ingredients were added to seven C. acnes strains, including type strains of the three subspecies (types I, II, and III), and their effects were evaluated by monitoring growth curves based on turbidity measurements.

Results

All strains exhibited growth inhibition in response to high concentrations (10 % v/v) of ethanol and glycerol, whereas low concentrations (3 % and/or 1 % v/v) of ethanol enhanced bacterial growth. The nonionic detergent Tween 80 significantly enhanced the growth of type I strains, with some strains also producing insoluble precipitates, which may relate to comedogenesis. In contrast, type III strains did not produce precipitates. The two polyamines, putrescine and spermidine, elicited a biphasic response, with growth inhibition observed at higher concentrations and growth promotion at lower concentrations.

Conclusion

The response of C. acnes subspecies/strains to the cosmetic components varied with the different ingredient concentrations, often exhibiting opposite effects.