Benzoyl peroxide (BP) is a widely available, over-the-counter medication and a mainstay in acne treatment. Its effectiveness is well-established, primarily stemming from its ability to combat acne-associated bacteria. However, as the importance of the body’s microbial populations is increasingly recognized, questions have arisen about the scope of BP’s action. The main concern is whether this potent antibacterial agent harms the “good” bacteria necessary for skin health. This article explores the precise mechanism of benzoyl peroxide and its impact on microbial communities both on and within the body.
How Benzoyl Peroxide Works
Benzoyl peroxide acts as an organic peroxide and functions as a non-specific oxidizing agent upon application to the skin. When it penetrates the skin, it is metabolized by cysteine, a naturally occurring amino acid. This decomposition releases reactive oxygen species, including free radicals, directly into the hair follicle and surrounding tissue.
These free radicals create a highly toxic environment for bacteria. Because the oxidation is non-selective, the reactive species damage bacterial proteins and DNA, leading to rapid cell death. This chemical action distinguishes BP from traditional antibiotics, which typically target specific biological pathways.
BP’s Effect on Acne-Causing Bacteria
The primary target of benzoyl peroxide is Cutibacterium acnes (C. acnes), a bacterium that significantly contributes to acne development. C. acnes is anaerobic, thriving in the low-oxygen, lipid-rich environment deep within clogged pores. The active oxygen released by BP is highly effective at disrupting this anaerobic habitat, quickly reducing the C. acnes population.
Clinical studies show that using a 10% BP formulation daily for two weeks can decrease C. acnes in hair follicles by nearly 98%. Because its mechanism involves broad, non-specific oxidation, C. acnes strains have not developed resistance to benzoyl peroxide. For this reason, BP is often combined with topical antibiotics to prevent the emergence of resistant strains.
Impact on the Skin’s Commensal Flora
Because of its non-specific oxidizing nature, BP’s effects are not limited solely to C. acnes. The skin hosts a diverse community of commensal, or “good,” bacteria that maintain the skin’s barrier function and regulate immunity. BP inevitably affects these beneficial microbial populations in the treated area.
Studies confirm that topical BP can cause a temporary shift and reduction in the diversity of the local microbial ecosystem. The relative abundance of certain bacteria, including Cutibacterium and Staphylococcus species, can be reduced after treatment. However, this disruption is localized to the application area and is considered transient.
The effect is far less severe than the widespread, systemic changes caused by oral antibiotics, which disrupt the microbiome across the entire body. The skin’s microbial diversity tends to recover once treatment is stopped or reduced. Using lower concentrations of BP or combining it with non-antimicrobial treatments can help minimize the impact while still managing acne effectively.
Benzoyl Peroxide and Internal Bacteria
A common concern is whether topical BP can travel through the bloodstream and impact the gut microbiota or other internal bacterial populations. This is not a concern for the average user, as benzoyl peroxide is minimally absorbed through the skin’s surface.
The small amount of BP that penetrates the skin is quickly converted into benzoic acid, a common compound often used as a food preservative. This metabolite is absorbed into the systemic circulation and rapidly excreted by the kidneys through the urine.
Due to the speed of this metabolic process and renal clearance, the absorbed product does not accumulate in the body. Therefore, BP applied to the skin does not reach the gut or other internal systems in a biologically active form or concentration that would affect internal bacterial communities.