Glycolic acid can improve the appearance of scars, particularly shallow atrophic (indented) acne scars and the dark marks they leave behind. It works by accelerating skin cell turnover on the surface while stimulating collagen production deeper down, gradually smoothing and evening out scarred skin over a series of treatments. It’s not a miracle fix for all scar types, though, and results depend heavily on the kind of scar, the concentration used, and how consistently you use it.
How Glycolic Acid Works on Scarred Skin
Glycolic acid is an alpha hydroxy acid (AHA) with the smallest molecular size in its class, which lets it penetrate skin more effectively than other AHAs. On the surface, it dissolves the bonds holding dead skin cells together, revealing fresher skin underneath. This exfoliation alone can make shallow scars and discoloration look less pronounced.
The more interesting action happens deeper. Glycolic acid increases the proliferation of fibroblasts, the cells responsible for producing collagen and other structural proteins in your skin. It also boosts hyaluronic acid levels in both the outer and deeper layers of skin, improving hydration and plumpness. Research published in the Journal of Cosmetic Dermatology found that collagen production increased in a concentration-dependent manner, and that even lower concentrations that don’t fully penetrate the deeper skin layers can still trigger collagen synthesis indirectly, through signals sent by surface skin cells to the fibroblasts below. Over time, this new collagen fills in depressed scars and improves the quality of elastic fibers, making skin look smoother and more resilient.
Which Scar Types Respond Best
Glycolic acid is most effective for atrophic scars: the shallow, indented marks left behind by acne, chickenpox, or minor injuries. Among atrophic scars, boxcar scars (broad depressions with defined edges) respond particularly well to glycolic acid peels. Rolling scars and shallow ice pick scars may also improve, though deeper ice pick scars typically need more aggressive treatments like punch excision or deep chemical peels with stronger acids.
For raised scars like hypertrophic scars or keloids, glycolic acid alone isn’t an effective treatment. These scar types involve excess collagen production, and the standard approaches include pressure therapy, corticosteroid injections, and laser therapy. If you have raised scars, glycolic acid won’t make them worse, but it’s not the right tool for the job.
Where glycolic acid really shines is with the dark or reddish discoloration that scars leave behind, known as post-inflammatory hyperpigmentation. By continuously shedding pigmented surface cells and encouraging new, evenly pigmented skin to take their place, it can noticeably lighten these marks over several weeks of use.
Professional Peels vs. At-Home Products
Glycolic acid products span a wide range of strengths, and the concentration and pH determine how deeply they work. At-home products, like cleansers, toners, and serums, typically contain 5% to 15% glycolic acid at a higher (gentler) pH. These are useful for mild discoloration and subtle texture improvements but won’t dramatically change the depth of a scar.
Professional chemical peels use concentrations between 20% and 70%, with pH levels as low as 2.3. Dermatologists classify these peels into three tiers:
- Very superficial: 30% to 50% glycolic acid, applied for 1 to 2 minutes
- Superficial: 50% to 70%, applied for 2 to 5 minutes
- Medium depth: 70%, applied for 3 to 15 minutes
For atrophic acne scars specifically, the best documented results come from 70% glycolic acid applied biweekly for five sessions. Practitioners generally start with a lower concentration (around 20%) and increase the strength and application time in subsequent sessions to gauge your skin’s tolerance. The higher the concentration and the lower the pH, the more intense the peel and the more dramatic the results, but also the greater the risk of irritation.
Realistic Timeline for Results
Glycolic acid is not a quick fix. If you’re using an at-home product, here’s roughly what to expect. In the first week or two, you’ll likely notice some flaking and peeling, particularly around the nose, mouth, and cheeks. This is normal exfoliation, not damage. By weeks two to four, skin texture starts feeling smoother, and makeup tends to go on more evenly. Shallow pigmentation and dullness begin to lift.
The more meaningful changes, like softening of scar edges, lightening of deeper post-acne marks, and improved skin tone, typically emerge between weeks 6 and 12 of consistent use. For professional peels done at intervals of two to three weeks, most treatment courses involve four to six sessions before a significant visible change. Stubborn discoloration and textural scarring generally need the full 6 to 12 week window, and sunscreen is non-negotiable during this time because glycolic acid makes your skin significantly more sensitive to UV damage, which can darken the very marks you’re trying to fade.
Combining Glycolic Acid With Other Treatments
Glycolic acid often works better as part of a combination approach than as a standalone treatment. A study of 60 patients with acne scars compared microneedling alone to microneedling combined with 35% glycolic acid peels. The combination group saw significantly better improvement in superficial and moderately deep scars (grades 1 through 3), along with better skin texture and greater reduction in post-acne pigmentation, without any increase in side effects or healing time.
For hyperpigmentation specifically, combining glycolic acid peels (at 50% concentration or higher) with topical treatments like azelaic acid and adapalene produced better results than either approach alone. The peel accelerates the removal of pigmented cells while the topical agents regulate melanin production between sessions.
How Glycolic Acid Compares to Other Acids
A comparative study of 35% glycolic acid peels versus a combination of 20% salicylic acid with 10% mandelic acid found that both treatments were effective and safe. However, the salicylic-mandelic combination was more effective for active acne lesions and post-acne hyperpigmentation. Glycolic acid’s advantage is its collagen-stimulating ability, which makes it better suited for textural scarring where you’re trying to fill in depressed areas rather than just lighten discoloration. If your main concern is dark marks without much indentation, a salicylic acid product may work just as well or better, especially if you have oily or acne-prone skin.
Safety for Darker Skin Tones
People with darker skin (Fitzpatrick types IV through VI) face a real risk of post-inflammatory hyperpigmentation from any treatment that irritates or inflames the skin, including chemical peels. With glycolic acid, this risk increases with medium to deep peels. The good news is that when used at appropriate concentrations, glycolic acid actually shows faster improvement in darker skin compared to topical lightening agents like hydroquinone and tretinoin alone. In studies of glycolic acid peels on darker skin, only about 5.6% of patients experienced adverse effects, including post-inflammatory hyperpigmentation, skin irritation, or herpes reactivation.
The key is starting at a low concentration, increasing gradually, and avoiding aggressive peel depths. If you have darker skin and want professional peels for scarring, look for a practitioner experienced with your skin type who will build up concentration slowly over multiple sessions rather than jumping to high strengths.