Ingredients

Glycolic Acid: The Complete Guide to This Powerful AHA Exfoliant

Learn how glycolic acid exfoliates skin, fades dark spots, and boosts collagen. Find the right concentration, usage tips, and product picks for your skin.

Glycolic Acid: The Complete Guide to This Powerful AHA Exfoliant

A 2003 study published in Dermatologic Surgery found that patients using 10% glycolic acid for 24 weeks showed significant improvement in skin texture, fine wrinkling, and mottled pigmentation compared to a vehicle control. Glycolic acid is the most widely studied alpha hydroxy acid in dermatology, and its small molecular size gives it a unique advantage — it penetrates skin more effectively than any other AHA on the market.

Quick Summary:

  • Glycolic acid is the smallest AHA molecule, allowing deeper penetration and more effective exfoliation than lactic or mandelic acid
  • Start with a low concentration (5–8%) two to three times per week and increase gradually to avoid irritation
  • Clinical research confirms glycolic acid improves texture, reduces hyperpigmentation, stimulates collagen, and helps clear acne
  • Always wear sunscreen when using glycolic acid — AHAs increase UV sensitivity by up to 18% according to FDA research
  • Results for texture appear in four to six weeks, while pigmentation and fine lines need eight to twelve weeks of consistent use

What Is Glycolic Acid?

Glycolic acid is an alpha hydroxy acid (AHA) derived from sugarcane. Among all AHAs — which include lactic acid, mandelic acid, citric acid, and tartaric acid — glycolic acid has the smallest molecular weight at just 76.03 daltons. This tiny size is the key to its effectiveness: smaller molecules penetrate the skin's outer layer more easily and more uniformly.

AHAs as a class work by dissolving the bonds between dead skin cells on the surface (the "glue" called desmosomes that holds corneocytes together). Glycolic acid does this more efficiently than larger AHAs because it reaches deeper into the stratum corneum. This is why glycolic acid is the gold standard for chemical exfoliation and the most commonly used AHA in both over-the-counter products and professional peels.

The pH of a glycolic acid product matters as much as its concentration. Glycolic acid works best at a pH between 3.0 and 4.0. Below pH 3.0, it becomes unnecessarily irritating without proportional benefit. Above pH 4.0, the acid becomes increasingly neutralized and less effective. For a deeper understanding of why pH matters, see our skincare pH guide.

How Glycolic Acid Works on Your Skin

Glycolic acid's benefits come from three distinct mechanisms that work simultaneously on different layers of your skin.

Chemical exfoliation. At the surface, glycolic acid breaks the ionic bonds between corneocytes (dead skin cells) in the stratum corneum. A study by Fartasch et al. in the British Journal of Dermatology (1997) showed that glycolic acid reduces corneocyte cohesion in a dose-dependent manner. This accelerated shedding reveals newer, smoother skin cells underneath — the same principle as physical exfoliation, but more uniform and controlled.

Collagen stimulation. At deeper levels, glycolic acid signals fibroblasts to produce more collagen and glycosaminoglycans. A study published in Experimental Dermatology (2003) by Bernstein et al. demonstrated that topical glycolic acid at concentrations of 20% or higher increased epidermal and dermal hyaluronic acid content and stimulated collagen gene expression. This dual action — surface renewal plus deeper structural support — is why glycolic acid improves both texture and firmness.

Melanin regulation. Glycolic acid accelerates the turnover of pigmented cells and interferes with melanin transfer between melanocytes and keratinocytes. A clinical study in the Journal of Cosmetic Dermatology (2010) found that 10% glycolic acid applied twice daily for 12 weeks produced significant improvement in melasma severity scores compared to the control group.

Clear glycolic acid liquid texture

Benefits of Glycolic Acid

Research supports glycolic acid for multiple skin concerns:

Skin texture and smoothness. This is where glycolic acid excels most visibly. By removing the buildup of dead cells that makes skin feel rough and look dull, glycolic acid produces noticeable smoothness within the first few weeks of use. If you struggle with rough, bumpy texture or keratosis pilaris, glycolic acid is a first-line treatment.

Hyperpigmentation and dark spots. Glycolic acid fades post-inflammatory hyperpigmentation, sun spots, and melasma through accelerated cell turnover. Pigmented cells are shed faster, and new, evenly pigmented cells replace them. For stubborn dark spots, glycolic acid pairs well with other brightening agents like niacinamide or vitamin C. Learn more about treating hyperpigmentation.

Fine lines and wrinkles. The collagen-stimulating properties of glycolic acid make it effective for early anti-aging. A 22-week study by Thibault et al. in the Journal of the American Academy of Dermatology (1998) showed that 8% glycolic acid reduced wrinkle depth, improved skin elasticity, and increased dermal collagen density in photoaged skin.

Acne and clogged pores. Glycolic acid prevents the dead cell buildup that clogs pores and triggers breakouts. While salicylic acid is generally preferred for acne because it's oil-soluble and penetrates into pores, glycolic acid works well for surface-level congestion and closed comedones. For a complete approach, see our acne treatment guide.

Verdict: Glycolic acid is the most effective AHA for improving skin texture, fading discoloration, and building collagen. Its small molecular size gives it an edge over gentler alternatives. If your skin can tolerate it, glycolic acid delivers faster, more visible results than any other over-the-counter AHA.

How to Choose the Right Glycolic Acid Product

Glycolic acid products range from gentle daily toners to concentrated peels. Choosing the right format and concentration depends on your experience level and skin sensitivity.

Daily-use products (5–10%). Toners, serums, and pads in this range are designed for regular use. The Ordinary Glycolic Acid 7% Toning Solution (around $9) is a popular entry point — it covers the face with a single application and doubles as a gentle body exfoliant. Good Molecules Overnight Exfoliating Treatment (around $12) combines glycolic acid with other AHAs for a comprehensive overnight peel.

Mid-strength products (10–15%). These are leave-on treatments for experienced users or as occasional weekly treatments. Paula's Choice 8% AHA Gel Exfoliant (around $34) uses glycolic acid at an effective concentration in a hydrating gel base that minimizes irritation. COSRX AHA 7 Whitehead Power Liquid (around $22) is another well-regarded option that combines glycolic acid with apple water for gentle but effective exfoliation.

Professional peels (20–70%). These concentrations should only be applied by licensed professionals. In-office glycolic peels typically use 30–70% concentrations for three to five minutes and produce dramatic results for texture, scarring, and hyperpigmentation. At-home peels above 15% carry real risk of chemical burns and permanent scarring.

Wash-off products. Glycolic acid cleansers have lower efficacy than leave-on products because the acid contacts skin for only 30–60 seconds. They're a reasonable starting point for sensitive skin but won't deliver the same results as a toner or serum left on the skin.

Glycolic acid exfoliation product set

How to Start Using Glycolic Acid

Follow this approach to build tolerance and minimize irritation:

Week 1–2: Apply a glycolic acid toner or serum (5–8%) once every three days in the evening. Start on clean, dry skin and follow with moisturizer.

Week 3–4: If your skin tolerates it well, increase to every other evening. Watch for persistent redness, stinging that lasts more than a minute, or flaking.

Week 5–8: Move to nightly use if your skin shows no signs of overexfoliation. Some people find every-other-night use is their long-term sweet spot.

Application tips:

  • Apply to clean, completely dry skin — moisture increases penetration and irritation
  • Wait two to three minutes before applying moisturizer to let the acid work at the correct pH
  • Never layer glycolic acid with retinol on the same night — alternate them on different evenings
  • Always apply broad-spectrum sunscreen the following morning, since AHAs increase UV sensitivity
  • Skip glycolic acid on days when your skin is irritated, sunburned, or freshly waxed

Common Mistakes to Avoid

Using too many exfoliants at once. Combining glycolic acid with salicylic acid, retinol, or other AHAs in the same routine overwhelms the skin barrier. Pick one exfoliating active and build your routine around it.

Ignoring the pH. A glycolic acid product with a pH above 4.5 is essentially a moisturizer with a fancy label. Check that the product pH is between 3.0 and 4.0 for real results.

Skipping sunscreen. AHAs make your skin more sensitive to UV radiation. Using glycolic acid without daily sunscreen is counterproductive — you'll create more sun damage and pigmentation than you're trying to fix.

Overexfoliating. Signs include persistent tightness, shiny-but-not-in-a-good-way skin, stinging when applying normally gentle products, and increased breakouts. If these appear, stop all exfoliation for one to two weeks and focus on moisturizer and barrier repair.

Expecting overnight results. Surface texture improves in four to six weeks. Pigmentation changes need eight to twelve weeks. Collagen improvements take three to six months. Consistency at the right concentration beats aggressive short-term use every time.

Frequently Asked Questions

What's the difference between glycolic acid and salicylic acid?

Glycolic acid is an AHA (alpha hydroxy acid) that works on the skin's surface, dissolving bonds between dead cells. Salicylic acid is a BHA (beta hydroxy acid) that's oil-soluble, allowing it to penetrate inside pores. For acne and oily skin, salicylic acid is generally more effective. For texture, pigmentation, and anti-aging, glycolic acid is the better choice.

Can you use glycolic acid every day?

Yes, once your skin has built tolerance. Start with two to three times per week and gradually increase. Many people with normal to oily skin use glycolic acid nightly without issues. Those with sensitive or dry skin may do better at three to four times per week long term.

What percentage of glycolic acid is best for beginners?

Start with 5–8% in a toner or serum. This concentration provides visible results while minimizing irritation risk. The Ordinary's 7% toning solution is a widely recommended starting point. Avoid anything above 10% until you've used a lower concentration for at least six weeks.

Can you use glycolic acid with retinol?

Yes, but not on the same night. Both increase cell turnover and can cause excessive irritation when layered together. The most effective approach is alternating nights — glycolic acid one evening, retinol the next. This gives your skin the benefits of both without the compounded irritation.

Does glycolic acid help with acne scars?

Glycolic acid can improve the appearance of superficial acne scarring by promoting cell turnover and collagen production. For shallow, discolored scars, regular use at 8–10% produces noticeable improvement over three to six months. Deep ice pick or boxcar scars require professional treatments like chemical peels at higher concentrations or laser resurfacing.

Is glycolic acid safe for dark skin tones?

Glycolic acid is effective and generally safe for all skin tones, but darker skin requires more caution. Higher concentrations and aggressive use can trigger post-inflammatory hyperpigmentation in Fitzpatrick skin types IV–VI. Start with a lower concentration (5%), increase slowly, and always pair with sunscreen. A patch test behind the ear for one week before facial use is a smart precaution.

Can glycolic acid cause purging?

Yes. By accelerating cell turnover, glycolic acid can push existing clogs to the surface faster than they would emerge naturally. Purging typically lasts two to four weeks and occurs in areas where you normally break out. If new breakouts appear in unusual locations or persist beyond six weeks, the product may be irritating your skin rather than purging it.

Should you use glycolic acid in the morning or at night?

Night is preferred. Glycolic acid increases sun sensitivity, so applying it at night gives your skin hours to absorb and begin working before UV exposure. If you use it in the morning, sunscreen is absolutely mandatory — though sunscreen should be part of your morning routine regardless.

How long does it take for glycolic acid to work?

Surface texture improvements appear in four to six weeks. Hyperpigmentation fading becomes noticeable at eight to twelve weeks. Fine line and collagen improvements develop over three to six months. These timelines assume consistent use at an effective concentration (7% or higher for leave-on products).

Can you use glycolic acid while pregnant?

AHAs like glycolic acid are generally considered safe during pregnancy at over-the-counter concentrations (under 10%), according to the American College of Obstetricians and Gynecologists. However, professional-strength peels (20%+ concentrations) should be avoided. Consult your healthcare provider before starting any new active ingredient during pregnancy.

What should you not mix with glycolic acid?

Avoid using glycolic acid on the same night as retinol, other AHAs or BHAs, vitamin C at high concentrations (above 15%), and benzoyl peroxide. These combinations can overwhelm the skin barrier and cause excessive irritation. You can still use all of these ingredients in your routine — just on alternating nights or at different times of day.

The Bottom Line

Glycolic acid is the gold standard AHA for skin texture, pigmentation, and collagen support. Start with a 5–8% concentration two to three times per week, build up gradually, and pair with sunscreen daily. Give it at least eight weeks of consistent use before judging results. The initial tingle is temporary — the smoother, brighter skin is lasting.

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