Benzoyl PeroxidevsMandelic Acid

Benzoyl peroxide decomposes on skin, generating benzoic acid and reactive oxygen species (peroxyl and hydroxyl radicals). Cutibacterium acnes is an obligate anaerobe thriving in oxygen-depleted follicles; BPO-derived oxygen creates an aerobic environment while free radicals cause non-specific oxidative damage to bacterial membranes, proteins, and DNA. Because this does not target a specific bacterial pathway (unlike antibiotics), C. acnes cannot develop resistance—BPO remains effective indefinitely. Mild comedolytic activity through oxidative effects on follicular keratin. Anti-inflammatory effects from neutrophil modulation. 2.5% achieves similar bacterial kill to 10% with less irritation.

Mandelic acid (152 Da, the largest common AHA) exfoliates through calcium chelation and corneodesmosome disruption like other AHAs, but its large molecular size results in slower, more even epidermal penetration with reduced risk of hot-spot irritation and stratum corneum over-exfoliation. Its phenyl ring confers partial lipophilicity, enabling penetration into the pilosebaceous unit and follicular infundibulum—unlike purely hydrophilic glycolic and lactic acids. Within pores, mandelic acid exerts mild comedolytic effects by disrupting keratinocyte cohesion in the follicular epithelium, similar to salicylic acid. It demonstrates antibacterial activity against Cutibacterium acnes (Propionibacterium acnes) through membrane disruption. Mandelic acid also inhibits tyrosinase and reduces melanosome transfer to keratinocytes, providing brightening benefits. This profile makes it particularly suitable for acne-prone skin, hyperpigmentation, and darker skin tones (Fitzpatrick IV–VI) where gentler exfoliation minimizes post-inflammatory hyperpigmentation risk.