Glycolic Acid
Glycolic Acid (AHA)
The smallest alpha-hydroxy acid (AHA), derived from sugarcane. Penetrates deeply for effective exfoliation. Accelerates cell turnover, improves texture, fades dark spots, and stimulates collagen at higher concentrations.
Benefits
Exfoliates, brightens, fades dark spots, improves texture, boosts collagen
Risks & concerns
Increases sun sensitivity (SPF mandatory). Can irritate at high concentrations (>10%). Start low, build up.
Best for
Avoid if
How it works
Glycolic acid works by weakening the ionic and hydrogen bonds that hold corneocytes together in the stratum corneum. The mechanism is pH-dependent: at pH 3 to 4, the free acid form dominates and drives desquamation, while at higher pH the neutralised salt form (glycolate) is essentially inert. This is why formulation pH is the most important variable beyond concentration. Glycolic acid at 10% pH 3.5 has roughly 60% of its molecules in active free-acid form; the same 10% at pH 5 has less than 10% active. Beyond surface exfoliation, glycolic acid stimulates dermal fibroblast activity at sustained use, increasing hyaluronic acid synthesis and modestly upregulating collagen production. These longer-term effects explain why AHA regimens produce not just smoother-feeling skin but measurably thicker epidermis at 6 to 12 months.
Clinical evidence
A 1996 Ditre et al. trial in the Journal of the American Academy of Dermatology was the first to demonstrate histological epidermal thickening with daily 8% glycolic acid over 6 months. A 2018 Kornhauser review pooled 11 controlled trials and found consistent 10 to 25% reduction in fine wrinkles at 12 to 24 weeks of 5 to 10% AHA use. For melasma, a 2011 split-face trial by Sharquie showed 70% glycolic acid chemical peels produced greater depigmentation than 20% salicylic peels with comparable irritation. The SCCS opinion SCCS/1601/18 capped consumer leave-on glycolic acid at 10% and chemical peels at pH 3.5 minimum for cosmetics. Professional peels above 20% are dermatology or aesthetic practice only. The increased UV sensitivity (roughly 30% over baseline) persists for a week after discontinuation, which is why sunscreen is non-negotiable during AHA regimens.
Dosing and protocol
Start at 5% glycolic acid twice a week in the evening for 2 weeks. Apply to clean dry skin, wait 10 minutes, then layer moisturiser. If well tolerated, increase to three times weekly, then every other night, and eventually every night at 7 to 10%. The Ordinary Glycolic Acid 7% toner is a standard starter at pH 3.6. Paula's Choice 8% AHA and Pixi Glow Tonic 5% are gentler alternatives. Above 10% OTC is not legal in the EU/UK for consumer leave-on. Professional peels (20 to 70%) are a separate dermatology protocol and do not count as daily skincare. Always apply SPF 30+ the next morning, and keep applying SPF for 7 days after a chemical peel.
Interactions with other actives
Do NOT layer glycolic acid with retinol, salicylic acid, or benzoyl peroxide in the same evening routine. Pick one exfoliating or irritating active per night. Glycolic + niacinamide is a classic safe pairing that some brands market in single formulations. Glycolic + hyaluronic acid is the standard post-exfoliation hydration step. Vitamin C in the morning plus glycolic at night is the standard dermatology AM/PM protocol. Avoid glycolic use within a week before or after a professional peel or laser treatment.
Common mistakes
The two most common glycolic acid mistakes. First, skipping SPF the next morning. Glycolic thins the stratum corneum and increases UV sensitivity by 30%; no SPF means paradoxical hyperpigmentation and accelerated ageing. Second, stacking multiple AHAs or AHA plus BHA in the same routine because 'they are different acids'. The stratum corneum does not care about the chemical difference; cumulative exposure crosses the barrier-disruption threshold and produces inflammation. Pick one acid at a time.
FAQ
Glycolic acid vs mandelic acid: which should I use?
Glycolic for photoageing and surface texture on normal to oily skin. Mandelic for darker skin tones or reactive skin because it has a larger molecular size (150 vs 76 Daltons) and penetrates more slowly, reducing irritation and hyperpigmentation risk.
Is glycolic acid safe during pregnancy?
Yes at typical cosmetic concentrations up to 10%. ACOG and NHS accept continued use. Professional peels above 30% are not recommended. See our pregnancy-safe skincare guide.
How long before I see results?
Smoother texture at 2 to 4 weeks. Fine lines measurably reduced at 12 weeks. Epidermal thickening on histology at 6 months. Discontinuation reverses surface benefits within 2 to 4 weeks.
Sources
Targets these concerns
Found in (2)
Technical details
- INCI name
- Glycolic Acid
- CAS Number
- 79-14-1
- Category
- exfoliant
- Comedogenic rating
- 0/5
- Also known as
- aha, alpha hydroxy acid