Glycolic AcidvsMandelic Acid

Glycolic acid disrupts ionic bonds between corneocytes (dead skin cells) in the stratum corneum by chelating calcium ions and lowering the calcium concentration at desmosomal junctions. This weakens corneodesmosome integrity and activates endogenous proteases (kallikrein 5 and 7), accelerating desquamation. At higher concentrations, glycolic acid penetrates the viable epidermis and dermis, where it stimulates keratinocyte differentiation and upregulates transforming growth factor-beta (TGF-β) signaling in fibroblasts. This promotes glycosaminoglycan (GAG) synthesis, type I and III collagen production via procollagen gene expression, and elastin remodeling. Its small molecular size (76 Da) and high water solubility give it the deepest penetration of any AHA. The exfoliation also improves barrier function over time by promoting proper corneocyte maturation and reducing stratum corneum compaction.

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.