Clinical Research on Glycolic Acid

A comprehensive review of the clinical evidence for glycolic acid - key studies, evidence quality, and what the research actually shows about its effectiveness.

Updated Feb 22, 2026

16 min read

Educational content only. This article is not personal medical advice. For guidance specific to your skin, medications, or conditions, consult a board-certified dermatologist.

Glycolic acid has been studied for over 50 years, making it one of the most researched ingredients in dermatology. The evidence base includes randomized controlled trials, systematic reviews, government safety studies, and decades of clinical use. But research quality varies enormously, and many popular claims about glycolic acid outrun what the evidence actually supports. This article reviews the landmark studies, evaluates what the research shows for each major use case, and helps you distinguish between well-supported findings and marketing claims dressed up as science [1].

Research History

50+ Years

Glycolic acid research began with Van Scott and Yu's landmark 1974 publication. The clinical evidence base now spans hundreds of studies across multiple indications.

Strongest Evidence

Acne & Texture

The highest-quality evidence supports glycolic acid for mild-to-moderate acne (systematic review of RCTs) and skin texture improvement (network meta-analysis).

Key Limitation

Few Large RCTs

Most glycolic acid studies have small sample sizes (under 50 participants). Large-scale, long-term randomized trials remain limited.

Landmark glycolic acid studies
Study	Year	Type	Key Finding
Van Scott & Yu	1974	Clinical observation	AHAs normalize abnormal keratinization
Bernstein et al.	2001	Clinical trial	20% GA increases collagen and hyaluronic acid
Ditre et al.	1996	Pilot clinical	AHAs reverse photoaging markers
Sharad	2013	Review	Comprehensive review of GA peel therapy
Tang & Yang	2018	Review	Dual effects of AHAs on skin

The Origin: Van Scott and Yu (1974)

The story of glycolic acid in dermatology begins with Eugene J. Van Scott and Ruey J. Yu at Temple University. In 1974, they published a study testing over 60 substances for their effects on keratinization - the process by which skin cells mature, harden, and eventually shed. Among all the compounds tested, alpha-hydroxy acids, and glycolic acid in particular, demonstrated the most profound ability to normalize abnormal keratinization in patients with ichthyosis, a group of genetic skin disorders characterized by severely thickened, scaly skin [2].

This was not a skincare study. Van Scott and Yu were investigating treatments for a medical condition. But their discovery - that glycolic acid could fundamentally alter how skin cells behave - launched an entire field of research and eventually an industry. By the late 1980s, dermatologists were applying the principles Van Scott and Yu had identified to cosmetic concerns: rough skin texture, acne, hyperpigmentation, and photoaging (premature skin aging caused by UV exposure).

What makes this study foundational is not just priority (being first) but replication. The keratolytic (skin-peeling and cell-loosening) mechanism Van Scott and Yu described has been confirmed by dozens of subsequent studies over five decades. Their work is as solid as foundational research gets.

Understanding How It Works: Mechanism of Action

Before evaluating clinical outcomes, it helps to understand the mechanism of action - how glycolic acid produces its effects at the cellular level.

Desmosome Disruption

Fartasch, Teal, and Menon (1997) provided the definitive mechanistic study using electron microscopy on human skin. They showed that 4% glycolic acid causes targeted breakdown of desmosomes - protein structures that act like rivets holding dead skin cells together - in the stratum disjunctum (the outermost layer of the stratum corneum). Critically, the deeper stratum compactum and the skin's lipid barrier structures remained intact, and transepidermal water loss (TEWL - moisture escaping through the skin) did not increase [3].

This finding is important because it means glycolic acid exfoliates selectively - removing the outermost dead cells without compromising the skin's actual barrier function. This explains why properly formulated glycolic acid products are generally well tolerated despite being genuinely acidic. For a deeper explanation of how glycolic acid works on the skin, see our how it works guide.

Collagen Stimulation

Bernstein et al. (2001) conducted the key human study on collagen. After three months of twice-daily application of 20% glycolic acid lotion, both type I collagen gene expression and hyaluronic acid content were significantly increased compared to vehicle-treated controls in human forearm skin [4].

This study is frequently cited as proof that glycolic acid "boosts collagen." That is a fair summary, but with an important caveat: the study measured collagen mRNA (the genetic instructions for making collagen), not collagen protein deposition itself. Increased mRNA expression strongly suggests increased collagen production, but it is not a direct measurement of new collagen appearing in the skin. The authors themselves noted that "longer treatment intervals may result in collagen deposition."

Antibacterial Activity

Yang et al. (2020) discovered that glycolic acid has direct, pH-dependent antibacterial activity against Cutibacterium acnes (formerly Propionibacterium acnes), the primary bacterium involved in acne. The non-ionized (free acid) form was more bactericidal (able to kill bacteria) than the ionized form, and glycolic acid killed C. acnes by disrupting bacterial cell membranes. Effectiveness was demonstrated at concentrations as low as 0.2% [5].

This finding is significant because it means glycolic acid helps acne through two distinct mechanisms: exfoliation (unclogging pores by removing dead cells) and direct antibacterial action (killing acne-causing bacteria). The pH-dependent nature of this antibacterial effect connects directly to the science of pH in skincare - the lower the pH, the more free acid, and the stronger the antibacterial effect.

Acne Evidence

What the Randomized Controlled Trials Show

The strongest individual RCT for glycolic acid in acne is Abels et al. (2011): a double-blind, placebo-controlled trial with 120 participants. A 10% glycolic acid emulsion at pH 4.0, used once daily as monotherapy (used as the sole treatment), significantly improved mild acne compared to placebo. Improvement was statistically significant by day 45. Tolerability was not different from placebo - meaning the active product did not cause more irritation than the inactive vehicle [6].

This study is notable for its design quality (double-blind, placebo-controlled, adequate sample size) and its use of a realistic consumer concentration (10% at pH 4.0, not a professional peel). It provides direct evidence that over-the-counter-strength glycolic acid works for mild acne.

Kaminaka et al. (2014) tested 40% glycolic acid peels at pH 2.0 in a split-face RCT with 26 participants. The peel side showed significantly greater improvement than the placebo side for moderate acne. The split-face design is considered particularly rigorous for topical studies because each patient serves as their own control, reducing the impact of individual skin variation [7].

The Concentration Paradox

One of the most interesting findings comes from Edraki et al. (2022), an RCT comparing 5% glycolic acid complex versus 20% glycolic acid for mild-to-moderate facial acne in 80 participants. Counter-intuitively, the 5% formulation outperformed the 20% formulation across multiple measures: total lesion count, inflammatory lesion count, skin hydration, and patient satisfaction [8].

This result challenges the "more is better" assumption and is consistent with the principle that free acid value, not nominal concentration, determines efficacy. Our concentration guide explains how to choose the right strength for your goals. A well-formulated 5% product at an optimal pH can deliver more meaningful active acid than a poorly formulated 20% product. It also suggests that formulation sophistication - the overall composition of the product beyond just glycolic acid - plays a substantial role in clinical outcomes.

Systematic Review: The Highest Level of Evidence

Castillo and Yousef (2018) conducted a systematic review of randomized controlled trials evaluating chemical peels for acne. Across 12 RCTs with 387 total participants, glycolic acid peeling was superior to placebo, with a relative risk of achieving excellent or good improvement of 2.30 (95% CI: 1.40–3.77). However, glycolic acid was not significantly more effective than salicylic acid or Jessner's solution when compared head-to-head [9].

This is an honest, evidence-based conclusion: glycolic acid peels work for acne (definitively better than doing nothing), but they are not clearly superior to other chemical peel agents. For consumers comparing glycolic acid to salicylic acid, the choice should be based on skin type, preferences, and tolerability rather than claims of superiority. Our glycolic vs. salicylic acid comparison explores this in detail.

Anti-Aging and Photoaging Evidence

Texture and Roughness: Strong Evidence

The strongest evidence for glycolic acid in anti-aging concerns skin texture and roughness rather than wrinkles specifically. Multiple RCTs have shown improvement in skin smoothness and overall photodamage scores:

Stiller et al. (1996) demonstrated that 76% of patients using 8% glycolic acid cream achieved at least one grade improvement in overall photodamage severity in a double-blind, vehicle-controlled trial [10].
Thibault et al. (1998) showed daily 5% glycolic acid was effective for treating signs of photoaging in a double-blind randomized trial [11].
Newman et al. (1996) found that 50% glycolic acid peels improved mild photoaging with histological confirmation in a double-blind vehicle-controlled study [12].

Wrinkles: Weaker Evidence Than You Might Expect

A 2025 network meta-analysis of 23 RCTs with 3,905 participants - the highest level of evidence synthesis available - found that glycolic acid was effective for reducing skin roughness but did not achieve statistical significance for improving fine wrinkles. Isotretinoin, retinol, and tretinoin were all superior for fine wrinkle reduction [13].

Collagen Without Inflammation

Narda et al. (2021) tested glycolic acid adjusted to pH 4 on human skin explants and found that it stimulated collagen production and induced desquamation (shedding of dead skin cells) without increasing pro-inflammatory TNF-alpha (an inflammation-signaling protein). This is clinically relevant because it demonstrates that partially neutralized formulations - the type found in consumer products - retain skin-rejuvenating properties without triggering the inflammatory cascade [14].

Hyperpigmentation Evidence

Post-Inflammatory Hyperpigmentation (PIH)

Burns et al. (1997) studied glycolic acid peels specifically in Black patients (Fitzpatrick IV, V, VI - a scale that classifies skin by its response to UV exposure) with post-inflammatory hyperpigmentation. Serial peels using up to 68% glycolic acid provided additional benefit beyond standard topical treatment, with minimal adverse effects. The peel group showed more rapid and greater improvement, reaching statistical significance [15].

This study is important not only for its positive findings but for addressing a population often underrepresented in dermatological research. However, the sample size was small (n=19), and PIH treatment in darker skin types carries the paradoxical risk of worsening pigmentation if the peel causes irritation. This underscores the need for professional supervision when using glycolic acid peels on melanin-rich skin.

Melasma

Multiple studies have evaluated glycolic acid for melasma (a type of stubborn, hormone-linked dark patches on the skin), a condition notoriously difficult to treat:

Sarkar et al. (2002) found that glycolic acid peels combined with topical hydroquinone and tretinoin produced greater improvement than topical therapy alone in dark-skinned patients [16].
A 2025 RCT comparing 12% glycolic acid to 20% azelaic acid in 80 melasma patients found no significant difference in effectiveness, but glycolic acid was more cost-effective [17].
Another 2025 RCT found that 50% glycolic acid peels were more effective than 80% lactic acid peels for melasma [18].

The evidence suggests glycolic acid provides modest improvement in melasma severity, typically as part of a multi-modal treatment approach rather than as monotherapy. Melasma tends to recur, and expectations should be managed accordingly.

The Mechanism: Beyond Exfoliation

Usuki et al. (2003) demonstrated that glycolic acid directly inhibits tyrosinase (the enzyme responsible for melanin production) - in cell culture studies. This suggests glycolic acid lightens pigmentation through two mechanisms: accelerated turnover of pigmented cells (exfoliation) and reduced melanin synthesis at the cellular level [19]. However, this was an in vitro (laboratory, not human) study using melanoma (skin cancer) cells, and the extent to which this mechanism operates in normal human skin at consumer concentrations requires further clinical validation.

Safety Evidence

Photosensitivity: The Most Important Safety Finding

The increased UV sensitivity caused by glycolic acid is the most clinically significant safety concern, and it is supported by strong evidence.

Kaidbey et al. (2003) conducted a randomized, double-blind study with 29 subjects. After four weeks of daily 10% glycolic acid at pH 3.5, UV sensitivity increased by approximately 18% (measured by minimum erythemal dose, or the least amount of UV needed to cause redness), and sunburn cell formation was enhanced. The increased photosensitivity reversed within one week of stopping treatment [20].

Kornhauser et al. (2009), in an NIH-funded study, confirmed that 10% glycolic acid increased UV-induced erythema, DNA damage, and sunburn cell formation in human skin. This study notably found that salicylic acid showed less UV-sensitizing effect [21].

These findings led the FDA to require that AHA-containing cosmetic products include sun protection warnings on their labeling. The photosensitivity effect is considered well established by both the FDA and the European SCCS [22].

Cancer Risk: Reassuring Evidence

A natural question arises: if glycolic acid increases acute UV sensitivity, does long-term use increase skin cancer risk?

The National Toxicology Program (NTP) addressed this directly in a large, government-funded study. Groups of 36 male and 36 female hairless mice were treated with 4% and 10% glycolic acid at pH 3.5 and exposed to simulated solar light over their lifespan. The result: glycolic acid did not alter photocarcinogenesis (the development of skin cancer from UV exposure). Despite enhancing acute UV sensitivity, it did not increase cancer development in this model [23].

This is an animal study, not a human trial, but it provides meaningful reassurance. The NTP is a US government body with no commercial interest, and the study design (long-term, adequate sample size, relevant concentrations) is robust. The evidence suggests that with proper sun protection, glycolic acid use does not carry long-term cancer risk.

The CIR Safety Assessment

The Cosmetic Ingredient Review Expert Panel issued its final safety assessment in 1998, concluding that glycolic acid is safe in cosmetic products at concentrations up to 10%, at pH 3.5 or greater, when the product includes sun protection directions. This assessment remains the industry reference standard and has not been substantially revised in the intervening decades [22].

The European Scientific Committee on Consumer Safety (SCCS) is more restrictive, limiting consumer leave-on products to 4% glycolic acid at pH 3.8 or higher.

Evidence Gaps and Limitations

Intellectual honesty requires acknowledging what we do not know, not just what we do.

Limited Large-Scale RCTs

Most glycolic acid studies have small sample sizes - typically 20–80 participants. While several studies reach the 100+ range (notably Abels et al. with 120), we lack the kind of 500+ participant mega-trials common in pharmaceutical research. This is partly because glycolic acid is classified as a cosmetic ingredient, not a drug, so the regulatory incentive and funding for large trials is limited.

Short Study Durations

Most studies follow participants for 8–24 weeks. Long-term data (years of continuous use) is largely absent. The Liu et al. (2021) study on keratosis pilaris is a rare exception with its 5-year follow-up - and it showed that benefits did not persist after discontinuation [24]. We lack similar long-term data for facial applications.

Formulation Variability

Clinical studies test specific formulations, not generic "glycolic acid." The vehicle (cream, gel, serum, solution), additional ingredients, buffering, and product pH all influence outcomes. A result from one formulation does not automatically apply to every product listing the same glycolic acid percentage. This is one reason why the free acid value concept is so important - it provides a more standardized way to compare what products actually deliver. You can use our free acid calculator to see exactly how much active acid a given formulation provides.

Publication Bias

Studies showing positive results are more likely to be published than studies showing no effect. This means the published literature may overstate glycolic acid's benefits. Systematic reviews and meta-analyses partially correct for this, which is why they sit at the top of the evidence hierarchy.

Limited Diversity

Many glycolic acid studies were conducted in populations that do not reflect global diversity. Studies specifically examining glycolic acid in Fitzpatrick IV–VI skin types exist but are limited in number and size. Burns et al. (1997) had only 19 participants. More research in diverse populations would strengthen the evidence base.

How to Evaluate Skincare Claims

The glycolic acid research landscape illustrates broader principles that apply to all skincare claims.

The Evidence Hierarchy

Not all studies are created equal. From strongest to weakest:

Systematic reviews and meta-analyses - Pool data from multiple studies. Best available evidence.
Randomized controlled trials (RCTs) - Gold standard for individual studies. Random assignment, blinding, and control groups reduce bias.
Cohort and comparative studies - Observe groups over time but lack randomization. More prone to confounding.
Case series and case reports - Individual patient accounts. Useful for rare events but cannot establish causation.
In vitro and animal studies - Provide mechanistic insight but results do not always translate to humans.
Expert opinion and narrative reviews - Lowest evidence level. Valuable for synthesis but subject to individual bias.

Red Flags in Skincare Research Claims

"Studies show..." without specific citations. Which studies? How many participants? What was the study design?
In vitro results presented as clinical evidence. A result in a petri dish does not mean the same thing happens on your face.
Cherry-picked endpoints. A study might show improvement in "skin brightness score" while wrinkle depth did not change. Selective reporting of favorable outcomes is common.
Brand-funded studies cited uncritically. Industry funding does not automatically invalidate a study, but it should be noted and methodology should be scrutinized.
Percentage claims without context. "50% improvement" sounds impressive, but improvement from what baseline? Over what time period? Compared to what control?

Summary: What the Evidence Actually Supports

Based on the totality of clinical evidence, here is an honest summary of what glycolic acid can and cannot do:

Well-Supported by Evidence

Improves mild-to-moderate acne (systematic review of RCTs; Castillo & Yousef 2018) [9]
Improves skin texture and roughness (network meta-analysis; multiple RCTs) [13]
Increases type I collagen mRNA and hyaluronic acid in human skin (vehicle-controlled human study; Bernstein 2001) [4]
Increases UV sensitivity during use (multiple RCTs; FDA-acknowledged) [20]
Has pH-dependent antibacterial activity against C. acnes (mechanistic study; Yang 2020) [5]
Safe at consumer concentrations (up to 10%, pH 3.5+) with sun protection (CIR assessment; NTP study) [22]

Supported but Requires Nuance

Helps hyperpigmentation and melasma - evidence exists, but typically as combination therapy. Melasma tends to recur.
Stimulates collagen - mRNA expression increases, but direct measurement of collagen protein deposition in skin requires more research.
Effective for photoaging overall - yes, but better for texture/roughness than for fine wrinkle reduction specifically. Retinoids are superior for wrinkles.

Commonly Claimed but Not Well-Supported

"Cures acne" - manages and improves acne; does not cure it.
"Eliminates wrinkles" - network meta-analysis did not find statistical significance for fine wrinkle improvement.
"Higher percentage = more effective" - the Edraki 2022 RCT directly contradicts this claim.
Works as a deodorant - theoretical plausibility but zero clinical studies.

References

1. Almeman AA. (2024). Evaluating the Efficacy and Safety of Alpha-Hydroxy Acids in Dermatological Practice: A Comprehensive Clinical and Legal Review. Clin Cosmet Investig Dermatol. doi:10.2147/CCID.S453243Review
2. Van Scott EJ, Yu RJ. (1974). Control of keratinization with alpha-hydroxy acids and related compounds. I. Topical treatment of ichthyotic disorders. Arch Dermatol. doi:10.1001/archderm.1974.01630100046011Clinical observation
3. Fartasch M, Teal J, Menon GK. (1997). Mode of action of glycolic acid on human stratum corneum: ultrastructural and functional evaluation of the epidermal barrier. Arch Dermatol Res. doi:10.1007/s004030050212Mechanistic study
4. Bernstein EF, Lee J, Brown DB, et al. (2001). Glycolic acid treatment increases type I collagen mRNA and hyaluronic acid content of human skin. Dermatol Surg. doi:10.1046/j.1524-4725.2001.00234.xControlled study
5. Yang AJ, et al. (2020). pH-Dependent Antibacterial Activity of Glycolic Acid: Implications for Anti-Acne Formulations. Sci Rep. doi:10.1038/s41598-020-64545-9Mechanistic study
6. Abels C, Kaszuba A, Michalak I, et al. (2011). A 10% glycolic acid containing oil-in-water emulsion improves mild acne: a randomized double-blind placebo-controlled trial. J Cosmet Dermatol. doi:10.1111/j.1473-2165.2011.00572.xRCT
7. Kaminaka C, Uede M, Matsunaka H, et al. (2014). Clinical evaluation of glycolic acid chemical peeling in patients with acne vulgaris: a randomized, double-blind, placebo-controlled, split-face comparative study. Dermatol Surg. doi:10.1111/dsu.12417RCT
8. Edraki K, et al. (2022). Effect of 5% glycolic acid complex and 20% glycolic acid on mild-to-moderate facial acne vulgaris. Chin Med J (Engl). doi:10.1097/CM9.0000000000002287RCT
9. Castillo DE, Yousef K. (2018). Chemical peels for acne vulgaris: a systematic review of randomised controlled trials. BMJ Evidence-Based Medicine. doi:10.1136/bmjopen-2017-019607Systematic review
10. Stiller MJ, Bartolone J, Stern R, et al. (1996). 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. doi:10.1001/archderm.1996.03890300047009RCT
11. Thibault PK, Wlodarczyk J, Wenck A. (1998). A double-blind randomized clinical trial on the effectiveness of a daily glycolic acid 5% formulation in the treatment of photoaging. Dermatol Surg. doi:10.1111/j.1524-4725.1998.tb04209.xRCT
12. Newman N, Newman A, Moy LS, et al. (1996). Clinical improvement of photoaged skin with 50% glycolic acid. A double-blind vehicle-controlled study. Dermatol Surg. doi:10.1111/j.1524-4725.1996.tb00347.xRCT
13. Multiple authors. (2025). Comparative efficacy of topical interventions for facial photoaging: a network meta-analysis. Sci RepNetwork meta-analysis
14. Narda M, Trullas C, Brown A, et al. (2021). Glycolic acid adjusted to pH 4 stimulates collagen production and epidermal renewal without affecting levels of proinflammatory TNF-alpha in human skin explants. J Cosmet Dermatol. doi:10.1111/jocd.13570Ex vivo study
15. Burns RL, Prevost-Blank PL, Lawry MA, et al. (1997). Glycolic acid peels for postinflammatory hyperpigmentation in black patients. A comparative study. Dermatol Surg. doi:10.1111/j.1524-4725.1997.tb00014.xComparative study
16. Sarkar R, Kaur C, Bhalla M, Kanwar AJ. (2002). The combination of glycolic acid peels with a topical regimen in the treatment of melasma in dark-skinned patients: a comparative study. Dermatol Surg. doi:10.1046/j.1524-4725.2002.02034.xComparative study
17. Multiple authors. (2025). Efficacy, safety, and cost-effectiveness of glycolic acid vs. azelaic acid in melasma. J Family Med Prim CareRCT
18. Multiple authors. (2025). 80% Lactic Acid Peel Versus 50% Glycolic Acid Peel for Melasma: A Randomised Clinical Trial. Indian J DermatolRCT
19. Usuki A, Ohashi A, Sato H, et al. (2003). The inhibitory effect of glycolic acid and lactic acid on melanin synthesis in melanoma cells. Exp Dermatol. doi:10.1034/j.1600-0625.12.s2.7.xIn vitro study
20. Kaidbey K, Sutherland B, Bennett P, et al. (2003). Topical glycolic acid enhances photodamage by ultraviolet light. Photodermatol Photoimmunol Photomed. doi:10.1034/j.1600-0781.2003.00013.xRCT
21. Kornhauser A, Wei RR, Yamaguchi Y, et al. (2009). The effects of topically applied glycolic acid and salicylic acid on ultraviolet radiation-induced erythema, DNA damage and sunburn cell formation in human skin. J Dermatol Sci. doi:10.1016/j.jdermsci.2009.03.011Controlled study
22. Andersen FA. (1998). Final Report on the Safety Assessment of Glycolic Acid, Ammonium, Calcium, Potassium, and Sodium Glycolates.... Int J Toxicol. doi:10.1177/109158189801700101Safety assessment
23. National Toxicology Program. (2007). Photocarcinogenesis study of glycolic acid and salicylic acid in SKH-1 mice. NTP Tech RepAnimal study
24. Liu J, et al. (2021). Clinical outcomes and 5-year follow-up results of keratosis pilaris treated by a high concentration of glycolic acid. World J Clin Cases. doi:10.12998/wjcc.v9.i18.4681Follow-up study

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