For your skin
A fruit-derived AHA that exfoliates and antioxidizes. It shares the same basic mechanism as glycolic and lactic acid but is weaker gram-for-gram; in practice you'll see it doing dual duty (a little exfoliation plus pH stabilisation) in multi-acid toners and serums. When it appears low on an ingredient list, it's adjusting pH; higher up, it's contributing real exfoliation.
Want the science? Keep reading ↓Mechanism of action
Tricarboxylic AHA that weakens corneocyte cohesion in the same way as glycolic and lactic acids; included in Van Scott's landmark 25%-AHA study (glycolic, lactic, citric) that drove ~25% epidermal thickening over 6 months. Its antioxidant effect derives from chelating transition metal ions that catalyse free-radical reactions. In modern formulations it is more commonly used at low concentrations as a pH adjuster and preservative-system booster than as a primary exfoliant, where glycolic and lactic acids are more potent at equivalent pH.
Why we tier this moderate
4 cited papers across 3 countries. The mechanism is well-described and there's at least one controlled trial in the literature, but we tier this Moderate rather than Strong to stay honest about how many specific papers we cite directly.
Cited research
Tang SC, Yang JH. Dual Effects of Alpha-Hydroxy Acids on the Skin. Molecules. 2018;23(4):863.
Yamamoto Y, Uede K, Yonei N, Kishioka A, Ohtani T, Furukawa F. Effects of alpha-hydroxy acids on the human skin of Japanese subjects: the rationale for chemical peeling. Journal of Dermatology. 2006 Jan;33(1):16-22. — Clinical-mechanistic study in Japanese subjects demonstrating AHA (including citric acid class) keratolytic and epidermal renewal effects as rationale for chemical peeling.
Bernstein EF, Underhill CB, Lakkakorpi J, et al. Citric acid increases viable epidermal thickness and glycosaminoglycan content of sun-damaged skin. Dermatologic Surgery. 1997 Aug;23(8):689-694. — Mechanistic study showing topical citric acid increased viable epidermal thickness and dermal glycosaminoglycans in sun-damaged skin, similar to glycolic acid and retinoic acid.
Ditre CM, Griffin TD, Murphy GF, Sueki H, Telegan B, Johnson WC, Yu RJ, Van Scott EJ. Effects of alpha-hydroxy acids on photoaged skin: a pilot clinical, histologic, and ultrastructural study. J Am Acad Dermatol. 1996;34(2 Pt 1):187-95.
Sources: 10 clinical journals and regulatory databases across the US, EU, Korea, Japan, and China. Every entry points to a specific document. See methodology for the full list and what each outcome label means.