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Glycolic acid: 3.5%
Glycolic Acid for Dark Spots: What the Evidence Covers
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Glycolic acid is one of the over-the-counter ingredients the American Academy of Dermatology (AAD) lists as able to fade existing dark spots, but the evidence differs sharply by type of spot: some support for post-acne marks, weak results for sun spots, and for melasma only professional peels used alongside prescription medicines. The AAD also states that a skin care product that irritates your skin can itself cause dark spots, which is why this page spends as much time on avoiding new marks as on fading old ones.
The sources are the AAD, DermNet NZ, Cleveland Clinic, the US Food and Drug Administration (FDA) and peer-reviewed abstracts, all read for this page. The journal papers were read as abstracts, not full text. Where no source answers a question, the page says so.
The Short Answer
| Kind of dark spot | What the sources we read support |
|---|---|
| Post-acne and post-injury marks (post-inflammatory hyperpigmentation) | The AAD names glycolic acid among over-the-counter options. One 12-week trial of a combined glycolic and phytic acid product reported improvement. Many such marks fade by themselves. |
| Sun spots (solar lentigines) | Weak. A glycolic peeling fluid did not clear them in one small study; weekly 50% peels gave a slight lightening in another. |
| Melasma | Trials of glycolic peels exist, but they are clinic peels with prescription priming. DermNet NZ warns peels can worsen melasma. |
Important: This page summarizes published research and dermatology guidance. It is not medical advice and cannot tell you what kind of spot you have. If a spot is new, changing, bleeding or itching, see a dermatologist before treating it yourself.
Which Kind of Dark Spot Do You Have?
The three common types behave differently, and a treatment that suits one can be the wrong tool for another. Telling them apart is a clinical judgement, so treat the descriptions below as orientation, not diagnosis.
- Post-inflammatory hyperpigmentation (PIH): flat marks left where skin was inflamed or injured. DermNet NZ describes it as temporary pigmentation that follows injury or an inflammatory disorder such as dermatitis or infection, located at the site of the original problem. The AAD lists a pimple clearing, a healed wound and an irritating product among the triggers.
- Sun spots (solar lentigines): marks from long-term UV exposure, covered in our sun exposure guide.
- Melasma: patches that, per the AAD, can be triggered by sunlight, birth control pills and even stress. It is a dermatologist-managed condition.
Post-Acne Marks and Other PIH
This is the type with the strongest case for glycolic acid, and the case is still moderate. The AAD's page on dark spots in darker skin tones says that once the cause is found and protected against, a product containing azelaic acid, glycolic acid, kojic acid, a retinoid or vitamin C can fade existing dark spots, and that in some cases the ingredient can also slow melanin production. Cleveland Clinic's dermatology source lists "lightens dark spots that result from mild sun damage or acne" among glycolic acid's effects.
The one at-home trial we found is Houshmand 2021 (abstract): a facial emulsion with 10% glycolic acid, 2% phytic acid and a soothing complex, tested for 12 weeks in American women with Fitzpatrick skin types II to VI. The abstract reports significant improvement in PIH, hyperpigmentation, texture and tone from week 4 through week 12. Two limits apply: the product combined several ingredients, so the result cannot be credited to glycolic acid alone, and the abstract gives no participant numbers.
The AAD adds a point that is easy to miss: a spot a few shades darker than your natural colour usually fades within 6 to 12 months once its cause stops, and deeper discolouration can take years. Treatment can speed fading, but much of the change may be time. DermNet NZ lists glycolic acid peels among PIH treatments while noting that "combinations of the treatments below are usually required for significant improvement," and that physical treatments such as peels "may also aggravate it by injuring the epidermis." For how quickly trials reported change, see our before-and-after timeline.
Sun Spots
The evidence is thin. A 1996 study of 10 women found that a q-switched ruby laser cleared actinic lentigines, while a commercial glycolic acid peeling fluid caused burning and scaling and could not clear them. In a double-blind trial of 41 volunteers, 50% glycolic acid applied for five minutes once weekly for four weeks gave a slight lightening of solar lentigines alongside improvements in texture. That is a professional-strength peel. A 2025 systematic review of 41 trials concluded laser therapy appears more effective than other modalities, and its abstract does not name glycolic acid. Sunscreen matters here more than any acid, since the marks come from UV.
Melasma
Melasma is where an at-home glycolic acid product is least supported. The AAD says there is no one best treatment, that dermatologists often prescribe hydroquinone, tretinoin or a triple combination cream, and that a chemical peel may be added when melasma proves stubborn, performed only by a board-certified dermatologist. DermNet NZ says peels "can be used with caution, but carry a risk of worsening melasma or causing post-inflammatory hyperpigmentation," and that patients should be pretreated with a tyrosinase inhibitor such as hydroquinone.
The trials fit that picture:
- Sarkar 2016 (abstract): 90 Indian patients with melasma, fortnightly peels for 12 weeks. A 35% glycolic acid peel cut the melasma severity score by 62.36%, against 60.98% for a salicylic-mandelic peel; the difference between them was not significant. Every group was first primed for four weeks with 4% hydroquinone and 0.05% tretinoin cream, and there was no unpeeled comparison group, so the figures do not show what the peel alone achieved. The authors found the salicylic-mandelic peel better tolerated.
- Sobhi 2012 (abstract): 14 Egyptian women with skin types IV to V, a 70% glycolic acid peel on one side and vitamin C iontophoresis on the other over six sessions. Both sides improved, and the vitamin C side did better.
Neither used an over-the-counter product. Even after a good result, DermNet NZ says melasma pigment may reappear on exposure to summer sun. The AAD says treatment usually takes 3 to 12 months to show results.
Glycolic Acid on Darker Skin
Darker skin has more at stake with irritation. Davis and Callender's 2010 review says PIH tends to affect darker-skinned patients with greater frequency and severity, and that it is important to use caution with all the treatments they list "to prevent irritation and worsening of postinflammatory hyperpigmentation." DermNet NZ similarly says PIH is more common in darker-skinned people, in whom the colour tends to be more intense and to persist longer.
The AAD's advice for darker skin tones is practical: if a product irritates, use gentler ones; if it burns or stings when you apply it, stop; and when irritation settles, new dark spots tend to stop appearing. The FDA's review of 114 adverse-event reports on AHA products between 1992 and February 2004 included 15 reports of pigmentary changes. That is a count of reports, not a rate, and it does not break results down by skin tone.
What we could not establish: whether glycolic acid carries more or less risk on darker skin than other exfoliants. A 2013 review of glycolic acid peels says in its abstract that they are very safe with Fitzpatrick skin types I to IV, and says nothing about types V and VI. Houshmand 2021 included types II to VI but does not report results by type. The AAD also warns that some imported skin-lightening products contain unlabelled steroids or mercury and that liquid bleach should never go on skin, so a gentle, clearly labelled product is the safer route.
Strength and Format
No source we read gives a starting strength for dark spots. What exists is general: Cleveland Clinic's dermatology source suggests starting once or twice a week and working up to nightly use if skin is tolerating it, and to test a small area first. The FDA reports that the industry's Cosmetic Ingredient Review panel found 10% glycolic acid at pH 3.5 or higher safe for consumer products when formulated to avoid increasing sun sensitivity or used with daily sun protection. The label percentage is a total; the free acid value depends on pH, as our percentage guide explains.
Our reading, which is an inference and not a sourced rule: since irritation is the main way an acid can worsen marks, the cautious choice is a low free acid value in a leave-on product you can stop at once. Two catalogue products illustrate the low and moderate ends.
Good Molecules states 3.5% glycolic acid for this toner. Our catalogue holds no published pH for it, so its free acid value cannot be calculated.
✓ Glycolic acid verified
The Ordinary Glycolic Acid 7% Exfoliating Toner
Glycolic acid: 7%
The Ordinary states 7% glycolic acid and a pH of 3.5 to 3.9. By the percentage guide's arithmetic (Henderson-Hasselbalch at a pKa of 3.83), that is about 3.2% to 4.8% free acid; that range is our calculation, not a figure the brand publishes.
Neither product has been tested for dark spots in a study we read, so these are examples of strengths, not evidence of results. Both are sun-sensitising, as the next section explains.
Why Sunscreen Is Part of Treating Dark Spots
The AAD says effective treatment for dark spots begins with sunscreen, and recommends a tinted sunscreen with iron oxide, which protects against visible light, a cause of dark spots. It lists SPF 30 or higher, broad-spectrum and water-resistant as the features to look for, reapplied every two hours. DermNet NZ advises SPF 50+ for PIH on exposed skin. Our house line is SPF 30+ as a minimum margin. Because glycolic acid raises UV sensitivity while you use it and for about a week afterwards, as covered in our sun exposure guide, an acid without sun protection can work against fading.
Common Mistakes
- Treating irritation as a sign it is working. The AAD says a product that burns or stings should be stopped.
- Treating melasma like a post-acne mark. Peels can worsen melasma, per DermNet NZ.
- Skipping the cause. The AAD says that to clear PIH from acne, the acne itself must be treated first.
- Using unlabelled lightening products. The AAD warns of hidden steroids and mercury in some imports.
- Expecting a fixed timetable. Fading can take 6 to 12 months or longer even when everything goes right.
Sources Used for This Page
- AAD, How to fade dark spots in darker skin tones.
- AAD, Melasma: Diagnosis and treatment; AAD, Finding skin cancer in darker skin tones.
- DermNet NZ, Postinflammatory hyperpigmentation and Melasma.
- Cleveland Clinic, How Should You Use Glycolic Acid? (25 November 2025).
- FDA, Alpha Hydroxy Acids.
- PubMed abstracts: Davis 2010, Houshmand 2021, Sarkar 2016, Sobhi 2012, Kopera 1996, Newman 1996, Mardani 2025, Sharad 2013.
For how this site chooses and cites sources, see the methodology on our About page.
Frequently Asked Questions
Does glycolic acid fade dark spots, and which kind?
It depends on the kind, and the evidence differs for each. For post-acne marks (post-inflammatory hyperpigmentation), the American Academy of Dermatology lists glycolic acid among over-the-counter ingredients that can fade existing dark spots, and a 12-week trial of a 10% glycolic and 2% phytic acid emulsion reported improvement from week 4 (Houshmand 2021). For sun spots, a 1996 study found a glycolic peeling fluid could not clear them, while weekly 50% peels gave only a slight lightening. For melasma, the evidence we found is professional peels used with prescription priming, not at-home products.
Is glycolic acid safe on darker skin, or can it cause new dark marks?
Irritation is the risk to manage. Davis and Callender say post-inflammatory hyperpigmentation tends to affect darker skin with greater frequency and severity, and that caution is needed with every treatment 'to prevent irritation and worsening of postinflammatory hyperpigmentation.' The AAD says a skin care product that irritates your skin can itself cause dark spots, and that a product that burns or stings should be stopped. We found no source that rates glycolic acid as safe or unsafe for darker skin as a group; the one at-home trial we read, Houshmand 2021, enrolled Fitzpatrick skin types II to VI and reported it was well tolerated.
What strength and format of glycolic acid should you start with for dark spots?
No source we read names a starting strength for dark spots. Cleveland Clinic's dermatology source advises starting once or twice a week and working up to nightly use only if skin tolerates it, and the CIR panel's consumer ceiling, as the FDA reports it, is 10% glycolic acid at pH 3.5 or higher. Free acid, not the label percentage, is what reaches skin; our percentage guide shows how to calculate it. Our reading, not a sourced rule: with irritation the main risk, a lower free acid value and a leave-on format you can stop quickly are the cautious end.
How long before you see a change in dark spots?
The AAD says a spot a few shades darker than your natural skin colour usually fades within 6 to 12 months once its cause is stopped, and Cleveland Clinic's source says over-the-counter glycolic acid may take several months. Our before-and-after timeline covers the trial timelines in detail.
What makes dark spots come back?
The AAD calls the sun's visible light a cause of dark spots and says sunscreen can prevent new ones. It also says to keep addressing the cause, such as continuing to treat a skin condition, and that hyperpigmentation fades in time if you don't re-injure your skin. DermNet NZ adds that even after a good result, melasma pigment may reappear on exposure to summer sun. Glycolic acid also raises sun sensitivity while you use it (see our sun exposure guide), so skipping sunscreen works against the goal.
Glycolic acid or something else for dark spots?
The AAD lists azelaic acid, glycolic acid, kojic acid, retinoids and vitamin C together as over-the-counter ingredients that can fade dark spots and does not rank them. We compare glycolic acid directly with vitamin C, niacinamide, retinol and mandelic acid, each with what the sources do and do not show.
When is a dark spot a reason to see a doctor instead?
See a dermatologist for any spot that is new, growing, bleeding, itching or changing, or for a dark line or streak in a nail. The AAD lists these as possible signs of skin cancer, and a cosmetic acid is not the right response to them. The AAD also says to see a dermatologist if the treatment you are using is not delivering results, since some dark spots need prescription-strength treatment, and melasma is typically managed by dermatologists with prescription medicines and sun protection.