The water-soluble exfoliant family — glycolic, lactic, mandelic, malic, tartaric, citric — that resurfaces the stratum corneum by loosening corneocyte adhesion. The 2025 conversation has moved from 'how high a percentage' to 'which acid for which skin': mandelic for sensitive and melanin-rich skin, lactic for hydration-leaning resurfacing, glycolic for stubborn texture. Drunk Elephant's TLC Framboos is the indie-blend benchmark.
Benefits
loosens stratum corneum adhesion for resurfacing
improves tone, texture, and post-inflammatory pigmentation
increases dermal glycosaminoglycan synthesis at appropriate doses
Example uses
resurfacing toners
weekly peel pads
tone-evening serums
Mechanism of action
Alpha-hydroxy acids are small water-soluble carboxylic acids that, at appropriate free-acid concentration and pH below their pKa, disrupt the ionic and disulfide bonds tethering corneocytes via sulphotransferase and transglutaminase modulation, accelerating desquamation. Sustained low-grade exposure also signals to fibroblasts to upregulate glycosaminoglycan and procollagen synthesis — the dermal-remodelling effect that justifies long-term use beyond surface exfoliation.
Clinical evidence · High
Decades of dermatology RCTs across glycolic, lactic, and mandelic on photoaging, PIH, and acne; the most-studied chemical exfoliant family in cosmetic science.
Effective concentration range
5–10% leave-on (pH 3.5–4) for OTC; EU caps glycolic at 4% leave-on as of 2024
Formulation notes
Buffered to pH 3.5–4 in leave-on systems. Free-acid percentage matters as much as labeled percentage — a 10% glycolic at pH 4.5 is much gentler than 10% at pH 3. Pair with humectants and barrier lipids; avoid stacking with retinol same routine.
Watchouts
Photosensitizing — daily SPF required. Over-exfoliation is the most common consumer mistake — barrier symptoms (stinging, redness) signal a pause. EU caps glycolic at 4% in leave-on consumer products as of 2024 — expect global re-formulation.
EU restriction of glycolic acid to 4% in leave-on consumer products (2024) reignited the 'is OTC over-exfoliation a public health issue' debate — driven by SCCS sensitisation and dermal-irritation data. The TikTok-fuelled 'acid-tox' culture of 2022–2024 produced a measurable rise in dermatologist visits for barrier dysfunction. Photosensitisation is real and under-communicated outside dermatology.
Market positioning
Sold as 'glow', 'resurfacing', and 'baby skin' — language that obscures the fact that AHAs are pharmacologically active controlled exfoliants, not skincare add-ons. The honest framing is closer to a low-dose medical resurfacing intervention with mandatory daily SPF.