Glycolic Acid

Overview

Glycolic acid is the smallest of the alpha-hydroxy acids (AHAs) — just two carbons, one hydroxyl group, one carboxylic acid. Its small size is its superpower: it penetrates the skin faster and deeper than any other AHA, which is why it produces the most visible results, but also why it is the most irritating.

It is naturally found in sugar cane, sugar beet, and unripe grapes. Cosmetic-grade glycolic acid is synthesized for purity and sold as a clear, water-thin liquid at 70-99% active concentration. It is the active ingredient in countless peel-pad products, “dermatologist-level” night serums, and professional 30-50% peels (which are not safe for DIY home use).

It is the AHA that built modern resurfacing skincare. The first wave of “anti-aging” routines in the 1990s was essentially glycolic acid at various percentages, and it remains the gold standard for visible texture improvement.

What it does in a formula

Primary roles:

• Surface and mid-depth exfoliation — dissolves cell-cell bonds in the stratum corneum and penetrates deeper than other AHAs
• Collagen stimulation — at 5%+ sustained use, glycolic acid measurably stimulates collagen synthesis in the dermis
• Brightening — fades hyperpigmentation, sun spots, and post-acne marks within 4-8 weeks
• Texture refinement — smooths rough patches, reduces visible pores, evens out tone

Secondary roles: improves the penetration of other actives applied afterwards (the freshly exfoliated surface absorbs better), and softens roughened areas like elbows, knees, and feet.

How to use

Add to the water phase. Heat-stable; can go in heated water phase or cool-down. Most formulators add it cool-down.

Usage range:

• Beginner serums: 1-3% (start here, build tolerance over weeks)
• Standard daily strength: 5-7%
• Resilient skin / weekly stronger: 8-10%
• Above 10%: professional-only, not for DIY home use

The 70% liquid form is the standard supplier offering. To convert: a 5% finished glycolic-acid serum from a 70%-active liquid requires 7.1% of the liquid (5 / 0.70 = 7.14%).

pH is critical. The protonated (free acid) form is what does the exfoliation. Final formula pH must be 3.5-4 for active exfoliation. Above pH 4 it converts to glycolate and stops working. Adjust with sodium hydroxide solution (carefully) to neutralize partway. Use a calibrated pH meter.

Photosensitivity: glycolic acid is the most photosensitizing of the AHAs. SPF 30+ is mandatory the day after use. Skipping sunscreen after a glycolic acid night undoes all the brightening work.

EU regulation: glycolic acid is permitted up to 10% in leave-on cosmetics for general use; concentrations above 6% should be labeled with a sun-sensitivity warning per the 2024 SCCS recommendation. Higher concentrations are restricted to professional use.

Best for / Worst for

Best for: resilient, oily, or thick skin types that tolerate strong exfoliation; visible photo-aging; deep-set hyperpigmentation; texture and pore concerns; mature skin (30+) with established tolerance to AHAs.

Worst for: sensitive skin (use lactic or mandelic instead), thin or compromised barriers, darker skin tones prone to post-inflammatory hyperpigmentation (mandelic acid is safer), dry skin (it lacks the hydration benefit of lactic acid), pregnancy and breastfeeding (caution above 5%), the eye area, anyone who refuses to wear daily sunscreen.

Common pitfalls

Skipping the pH check. A 7% glycolic acid serum at pH 5 is essentially inactive. Test and adjust to 3.5-4.

Starting too strong. 7-10% is too much for first-time AHA users. Start at 3-5% twice a week, build over 6-8 weeks.

Overusing. Daily 10% leaves most people with chronic redness and a thin, sensitized barrier within a month. Less is more.

Stacking with retinol or BHA in the same routine. A glycolic-acid night plus a retinol night plus a salicylic-acid morning is too much for almost any skin. Alternate or pick one primary active.

Not wearing SPF the next day. The biggest mistake. Glycolic acid massively increases UV sensitivity for up to a week.

Trying to do a “professional peel” at home. 30%+ glycolic acid peels require buffering, neutralizing solutions, and clinical training. Keep DIY use under 10%.

Substitutes

• Lactic acid — bigger molecule, gentler, also hydrating. Best alternative for sensitive skin.
• Mandelic acid — largest AHA, slowest-penetrating, best for darker skin tones and acne-prone skin.
• Salicylic acid — oil-soluble BHA, different mechanism, exfoliates inside pores.
• Polyhydroxy acids (PHAs) — gluconolactone and lactobionic acid, very gentle but effective for sensitive skin.
• Azelaic acid — different acid family, brightening and anti-acne, much gentler than glycolic.
• Tartaric acid — fruit-derived AHA, less common but valid alternative.