Glycolic Acid
Glycolic acid is an alpha-hydroxy acid (AHA) — the smallest AHA, derived from sugar cane. It's water-soluble, so unlike oil-soluble salicylic acid it works mainly on the skin's surface: it loosens the bonds between dead cells so they shed, leaving skin smoother, brighter and more even in tone. It also raises sun sensitivity, so daily sunscreen is required.
- Name
- Glycolic Acid
- INCI Name
- Glycolic Acid
- CAS Number
- 79-14-1
- Molecular Formula
- C2H4O3
- Molecular Weight
- 76.05 g/mol
- Category
- Alpha-hydroxy acid (chemical exfoliant)
- Also known as
- AHA · Alpha-hydroxy acid · 2-Hydroxyacetic acid · Hydroxyacetic acid
Overview
CosIng lists glycolic acid as an exfoliant and buffering agent. Its small size lets it penetrate the surface layers well and act as a keratolytic — dissolving the 'cement' between dead corneocytes so they exfoliate. Best-known for smoothing texture, brightening dull skin and evening tone. Because it thins the protective dead-cell layer, it increases UV sensitivity — the FDA requires a sunburn warning on AHA products.
How it works
Glycolic acid is a hydrophilic (water-soluble) AHA and the smallest of them, which lets it penetrate the upper epidermis readily. It is keratolytic: it reduces the cohesion between dead corneocytes in the stratum corneum so they shed, revealing smoother, brighter skin and helping even out pigmentation. At the low concentrations in leave-on cosmetics (commonly up to ~10%, EU up to 4%), this is primarily surface exfoliation. The deeper remodeling effects — increased collagen and dermal changes — are seen mainly at professional peel strengths (15-70%), not daily leave-on products. Because exfoliation removes protective surface cells, glycolic acid increases photosensitivity, so daily sunscreen is essential.
Keratolytic exfoliationhuman
Reduces cohesion between dead skin cells so they shed — the core, well-supported action behind smoother texture and brighter tone.
Small-molecule surface penetrationmechanistic
As the smallest AHA and water-soluble, it penetrates the upper epidermis more readily than larger AHAs — but acts mainly at the surface at cosmetic strengths.
Pigment / photoaging effects (dose-dependent)human
Improves uneven pigmentation and signs of photodamage; the stronger effects (including any dermal remodeling) require peel-strength concentrations, not leave-on.
Reported benefits
- Smooths & brightens — sheds dull surface cells for smoother texture and a brighter look; the best-supported benefit, seen even with low-strength leave-on use.
- Evens tone & pigmentation — helps fade uneven pigment and melasma; strongest results come from professional peels, more modest from daily products.
- Softens signs of photoaging — a vehicle-controlled trial found 8% glycolic cream improved overall photodamage vs placebo over 22 weeks.
- Best for surface concerns / normal-to-dry skin — water-soluble and surface-acting, it suits dullness, texture and tone (where oil-soluble salicylic acid better suits clogged pores).
Evidence
Moderate
Graded moderate. A double-blind vehicle-controlled trial found 8% glycolic acid cream improved photodamage over 22 weeks (Stiller 1996), and a systematic review of 24 studies found glycolic acid the most safe and effective peel for melasma (Sarkar 2024), on an established keratolytic mechanism. Not higher because the strongest effects require peel strengths (15-70%) rather than the low concentrations in leave-on products, benefits are largely surface exfoliation, it increases sun sensitivity, and the AHA cosmetic field carries a commercial founder lineage (Van Scott/Yu, NeoStrata) worth weighing in the literature.
Forms & derivatives
Related: Salicylic Acid
References
- Topical 8% glycolic acid and 8% L-lactic acid creams for the treatment of photodamaged skin: a double-blind, vehicle-controlled clinical trial Arch Dermatol. (Academic study (Dermatology Clinical Investigations Unit, Massachusetts General Hospital, Boston); no competing-interests statement in the 1996 record and funding not verified from the abstract — not asserted independent.)Double-blind vehicle-controlled RCT (74 women, 22 weeks): 8% glycolic acid cream significantly improved overall photodamage severity vs vehicle (76% vs 40% achieving >=1 grade of improvement).Human StudyPMID: 8651713 →
- Chemical Peels for Melasma: A Systematic Review Dermatol Surg. (Academic systematic review (Lady Hardinge Medical College, New Delhi); no competing-interests statement appears in the PubMed record.)Systematic review of 24 studies (n=1,075): glycolic acid was found to be the most safe and effective chemical peel for melasma.Reviewdoi:10.1097/DSS.0000000000004167 →
Frequently Asked Questions
Glycolic acid (AHA) vs salicylic acid (BHA) — which should I use?
Glycolic is an AHA: water-soluble, surface-acting, best for dullness, texture and uneven tone. Salicylic is a BHA: oil-soluble, gets into pores, best for blackheads, whiteheads and oily/acne-prone skin. Dry or sun-damaged skin often leans glycolic; congested, oily skin leans salicylic. See our salicylic acid page for the pore side.
Does glycolic acid boost collagen or 'rebuild' skin?
At the low strengths in daily leave-on products, mostly no — it's surface exfoliation that makes skin look smoother and brighter. The deeper effects people cite (collagen, dermal changes) come from professional peels at 15-70%, a different treatment with more risk.
Do I really need sunscreen with glycolic acid?
Yes — it's not optional. Glycolic acid removes protective surface cells and increases UV sensitivity; the FDA requires a sunburn-alert warning on AHA products. Use daily sunscreen while using it and for about a week after stopping.
What strength should I use?
Consumer leave-on products are typically up to ~10% (EU caps at 4%); professional peels run 15-70%. For daily use, higher isn’t better — it raises irritation. Start low and infrequent, especially if new to acids.
Can I use it with retinol or vitamin C?
Cautiously and usually not all at once — stacking acids and retinoids can over-irritate. Many alternate nights or use them at different times of day, and always with sunscreen. Introduce one active at a time so you can tell what your skin tolerates.
Is glycolic acid safe in pregnancy?
Low-strength topical glycolic acid is generally considered acceptable in pregnancy, though high-strength peels are usually avoided. As always, check with your doctor about your specific products.