Glycolic Acid vs Other AHAs: The Complete Comparison

Glycolic acid is the most widely studied alpha hydroxy acid, but it is not the only one. The AHA family includes lactic, mandelic, tartaric, citric, and malic acids - each with a different molecular weight, penetration profile, and set of secondary effects. Beyond AHAs, polyhydroxy acids (PHAs) like gluconolactone and lactobionic acid offer even gentler alternatives. This guide compares glycolic acid to every major member of the hydroxy acid family so you can choose the right one for your skin.

The Molecular Weight Hierarchy

All AHAs work through the same fundamental mechanism: they disrupt corneodesmosomes - the protein structures that bind dead cells together in the stratum corneum [1]. The smaller the acid molecule, the more easily it slips between tightly packed cells, and the deeper it penetrates before losing potency.

This is not theoretical. Van Scott and Yu's foundational 1974 research on alpha hydroxy acids established that molecular size directly correlates with the depth and speed of keratolytic effects [2]. Fartasch et al. (1997) later confirmed through electron microscopy that glycolic acid targets specific desmosomal structures in the outermost cell layers [3].

Here is the molecular weight hierarchy for the major hydroxy acids:

| Acid | Molecular Weight | Source | Relative Penetration | |------|-----------------|--------|---------------------| | Glycolic acid | 76.05 Da | Sugarcane | Deepest / fastest | | Lactic acid | 90.08 Da | Milk sugars | Deep / moderate | | Malic acid | 134.09 Da | Apples | Moderate | | Tartaric acid | 150.09 Da | Grapes | Moderate / shallow | | Citric acid | 192.12 Da | Citrus fruits | Shallow | | Mandelic acid | 152.15 Da | Bitter almonds | Shallow / gentle | | Gluconolactone (PHA) | 178.14 Da | Fermented corn | Very shallow / gentlest | | Lactobionic acid (PHA) | 358.30 Da | Oxidized lactose | Surface only / gentlest |

The pattern is clear: glycolic acid sits at one end of the spectrum (smallest, deepest, most potent) and the PHAs sit at the other (largest, most superficial, gentlest). Everything else falls in between.

Glycolic Acid vs Mandelic Acid

Mandelic acid is derived from bitter almonds and has a molecular weight of 152.15 Da - roughly twice that of glycolic acid. This makes it one of the gentlest AHAs, but it also has a unique property that sets it apart from other members of the family: partial lipophilicity. For a comprehensive comparison, see our dedicated glycolic acid vs mandelic acid guide.

The Lipophilicity Advantage

Most AHAs are water-soluble, which means they work on the water-rich stratum corneum surface but cannot penetrate through the oily sebum inside pores. Mandelic acid has a phenyl (aromatic) group in its structure that gives it partial oil solubility. This means mandelic acid has a degree of pore-penetrating ability that glycolic acid and other standard AHAs lack - though it does not match the full lipophilicity of salicylic acid (BHA) [4].

This partial lipophilicity, combined with its gentle penetration, makes mandelic acid an attractive option for people with acne-prone skin who find glycolic acid too irritating.

Better for Darker Skin Tones

Mandelic acid has gained particular attention for its suitability for Fitzpatrick skin types IV through VI. Aggressive exfoliation in melanin-rich skin can trigger post-inflammatory hyperpigmentation (PIH), making the treatment worse than the condition it was meant to address. Mandelic acid's slower, gentler penetration reduces this risk significantly [5].

Garg et al. (2009) compared glycolic acid peels to salicylic-mandelic acid peels and found them equally effective for active acne and hyperpigmentation, but the salicylic-mandelic combination was better tolerated and more suitable for Indian skin types [6]. Sarkar et al. (2012) recommended mandelic acid as one of the safer peel options for darker skin in their comprehensive review [5].

Head-to-Head

| Factor | Glycolic Acid | Mandelic Acid | |--------|--------------|---------------| | Molecular weight | 76 Da | 152 Da | | Penetration depth | Deep | Shallow | | Irritation risk | Higher | Lower | | Anti-aging evidence | Strong [7] | Limited | | Acne efficacy | Strong [8] | Moderate (partial lipophilicity helps) | | Suitability for dark skin | Requires careful protocols [9] | Better tolerated [5] | | Hyperpigmentation treatment | Strong evidence [10] | Good, with lower PIH risk | | OTC availability | Very common | Less common but growing |

Choose glycolic acid when you need maximum resurfacing power, have stubborn texture or hyperpigmentation, and your skin tolerates aggressive exfoliation. Choose mandelic acid when you have sensitive skin, darker skin tones, acne-prone skin that reacts poorly to glycolic acid, or you want gentle exfoliation with some pore-penetrating ability.

Glycolic Acid vs Lactic Acid

Lactic acid (90.08 Da) is the second most popular AHA and the closest competitor to glycolic acid. We cover this comparison in depth in our dedicated glycolic acid vs lactic acid guide, but the key points are:

• Lactic acid is about 18% larger than glycolic acid, resulting in shallower penetration
• Lactic acid has humectant properties - it draws moisture into the skin, making it uniquely suited for dry skin types
• Stiller et al. (1996) compared 8% glycolic acid and 8% lactic acid head-to-head in a double-blind RCT and found both effective for photodamage, with glycolic acid showing a slight edge [11]
• Kim et al. (1998) found glycolic acid produced greater collagen synthesis than lactic acid in vitro and in vivo [12]
• A 2025 RCT found 50% glycolic acid peels more effective than 80% lactic acid peels for melasma (P=0.009) [13]

In short: glycolic acid is more potent; lactic acid is gentler and more hydrating. Lactic acid is the better starting point for AHA beginners and dry or sensitive skin types.

Glycolic Acid vs Tartaric Acid

Tartaric acid is derived from grapes and has a molecular weight of 150.09 Da - about twice that of glycolic acid. It is one of the less commonly used AHAs in standalone skincare products, but it appears frequently in two contexts.

As a pH Adjuster

Tartaric acid is used in many cosmetic formulations not for its exfoliating properties but as a buffering agent to adjust and stabilize the pH of the product. Because skincare products containing AHAs need to maintain a specific pH range to be effective (ideally between 3.0 and 4.5 depending on the acid), tartaric acid serves a supporting role in multi-acid formulations.

In Wine-Based Skincare

Tartaric acid is a major component of grape-based and wine-based skincare products. While these products are marketed with associations to resveratrol and polyphenols, the exfoliating contribution of tartaric acid itself is mild compared to glycolic acid due to its larger molecular size and typically low concentrations.

Head-to-Head

| Factor | Glycolic Acid | Tartaric Acid | |--------|--------------|---------------| | Molecular weight | 76 Da | 150 Da | | Standalone exfoliant | Yes (primary use) | Rarely used alone | | Clinical evidence | Extensive | Very limited as standalone | | Primary role in products | Active ingredient | pH adjuster / co-ingredient | | Penetration depth | Deep | Shallow |

Verdict: Tartaric acid is not a meaningful competitor to glycolic acid for exfoliation. It functions primarily as a formulation ingredient. If a product lists tartaric acid, it is likely there for pH buffering, not as the primary active.

Glycolic Acid vs Citric Acid

Citric acid, derived from citrus fruits, has a molecular weight of 192.12 Da - more than 2.5 times that of glycolic acid. Like tartaric acid, citric acid is more commonly found as a supporting ingredient than a standalone exfoliant.

Antioxidant Properties

Citric acid's main differentiator from glycolic acid is its antioxidant activity. Citric acid can chelate (bind) metal ions that catalyze free radical formation, providing a degree of antioxidant protection that glycolic acid does not offer [4]. This makes citric acid a useful addition to formulations for its protective properties, independent of any exfoliating effect.

Exfoliating Limitations

At its molecular size (192 Da), citric acid penetrates the stratum corneum slowly and shallowly. It can produce mild exfoliation at high concentrations and low pH, but it is not competitive with glycolic acid for resurfacing purposes. Most products that include citric acid use it at low concentrations for pH adjustment and antioxidant benefits, not as a primary exfoliant.

Head-to-Head

| Factor | Glycolic Acid | Citric Acid | |--------|--------------|-------------| | Molecular weight | 76 Da | 192 Da | | Exfoliating potency | Strong | Weak | | Antioxidant activity | Minimal | Moderate (metal chelation) | | Primary role in products | Active exfoliant | pH adjuster / antioxidant | | Clinical evidence for exfoliation | Extensive | Very limited |

Verdict: Citric acid is not an alternative to glycolic acid for exfoliation. If you see it in a product, it is there for pH adjustment, antioxidant support, or both - not to compete with glycolic acid's resurfacing effects.

Glycolic Acid vs Malic Acid

Malic acid is derived from apples and has a molecular weight of 134.09 Da - sitting in the middle of the AHA molecular weight spectrum, between lactic acid and mandelic acid.

Less Studied Than Its Siblings

Malic acid has significantly less clinical evidence than glycolic or lactic acid for standalone skincare applications. Most of its use in skincare products is in multi-acid blends, where it contributes to the overall exfoliating and pH-buffering effect alongside more established AHAs.

Potential Unique Properties

Some researchers have noted that malic acid may have moisturizing properties similar to (though less pronounced than) lactic acid, owing to its hydroxyl groups. However, this has not been established in controlled clinical studies with the same rigor as the evidence for glycolic or lactic acid.

Head-to-Head

| Factor | Glycolic Acid | Malic Acid | |--------|--------------|------------| | Molecular weight | 76 Da | 134 Da | | Penetration depth | Deep | Moderate | | Clinical evidence | Extensive | Limited | | Standalone use | Common | Rare (usually in blends) | | Moisturizing properties | None | Mild (unconfirmed) |

Verdict: Malic acid is a reasonable component of multi-acid formulations but lacks the evidence base to recommend as a standalone alternative to glycolic acid. You are unlikely to find products that feature malic acid as their primary active ingredient.

Glycolic Acid vs PHAs (Polyhydroxy Acids)

Polyhydroxy acids represent the gentlest end of the hydroxy acid spectrum. The two most common PHAs are gluconolactone (178 Da) and lactobionic acid (358 Da). They were developed by Green, Yu, and Van Scott - the same researchers who pioneered AHA skincare - specifically to provide exfoliation for people who cannot tolerate AHAs [4].

How PHAs Differ from AHAs

PHAs are structurally similar to AHAs but have multiple hydroxyl groups, making them much larger molecules. Gluconolactone (178 Da) is more than twice the size of glycolic acid; lactobionic acid (358 Da) is nearly five times larger. This size prevents them from penetrating deeply into the stratum corneum, which dramatically reduces irritation while still providing surface-level exfoliation.

PHAs also have strong humectant properties - even more pronounced than lactic acid - because their multiple hydroxyl groups can bind more water molecules. Lactobionic acid in particular is an effective moisturizing agent [4].

Antioxidant and Protective Effects

Green et al. (2009) documented that PHAs have antioxidant and matrix-stimulating properties that go beyond simple exfoliation. Gluconolactone has demonstrated the ability to inhibit UV-induced damage markers in vitro, and lactobionic acid has shown matrix metalloproteinase inhibition - meaning it may help protect existing collagen from degradation [4].

Who Should Choose PHAs Over Glycolic Acid

PHAs are the best choice for:

• Rosacea-prone skin - rosacea flares easily with glycolic acid but PHAs are usually tolerated
• Extremely sensitive skin - people who react to even low-concentration AHAs
• Atopic dermatitis / eczema - compromised barrier function makes AHAs too aggressive
• Post-procedure skin - after laser treatments, microneedling, or other procedures where the barrier needs to heal
• People who cannot use sunscreen consistently - PHAs cause less UV sensitization than glycolic acid [14], though sunscreen is still recommended

Head-to-Head

| Factor | Glycolic Acid | Gluconolactone (PHA) | Lactobionic Acid (PHA) | |--------|--------------|---------------------|----------------------| | Molecular weight | 76 Da | 178 Da | 358 Da | | Penetration depth | Deep | Shallow | Surface only | | Exfoliating potency | Strong | Mild | Very mild | | Irritation risk | Moderate-high | Very low | Minimal | | Humectant properties | None | Moderate | Strong | | Antioxidant activity | Minimal | Moderate | Moderate | | UV sensitization | Yes (~18%) [14] | Minimal | Minimal | | Anti-aging evidence | Strong [7] | Limited | Limited | | Rosacea suitability | Poor | Good | Good |

Verdict: If your skin can tolerate glycolic acid, it will deliver more powerful results. But if your skin is too sensitive for AHAs - whether due to rosacea, eczema, or innate reactivity - PHAs offer real exfoliating benefit with dramatically less risk.

Multi-Acid Formulations: How Blends Work

Many modern skincare products combine multiple acids in a single formulation rather than relying on a single AHA. Understanding how these blends work can help you evaluate whether they are worth the typically higher price tag.

The Theory Behind Blending

Multi-acid formulations aim to deliver the benefits of several acids while keeping the concentration of any single acid low enough to minimize irritation. For example, a product might contain 3% glycolic acid, 3% lactic acid, and 2% mandelic acid - providing a total AHA concentration of 8% but with less irritation than 8% glycolic acid alone, because the larger acids (lactic, mandelic) temper the aggressive penetration of the glycolic acid.

The different molecular sizes also mean different acids reach different depths of the stratum corneum, potentially providing more even exfoliation from the outermost layers down to the deeper dead cell layers.

Clinical Evidence for Combinations

A prospective study by Decker and Graber (2020) found that over 90% of patients reported significant improvement in acne with combined glycolic acid and salicylic acid treatment [15]. The Edraki et al. (2022) RCT demonstrated that a 5% glycolic acid complex outperformed 20% glycolic acid alone for mild-to-moderate acne in terms of total lesions, inflammatory lesions, and patient satisfaction - suggesting that well-formulated lower-concentration blends can outperform higher-concentration single acids [16].

These findings align with the principle that free acid value - not nominal concentration - determines efficacy. A thoughtfully formulated multi-acid product can deliver meaningful results with less irritation than a crude high-concentration single acid.

What to Look For in Multi-Acid Products

• Listed concentrations and pH. Products that disclose total AHA percentage and pH allow you to evaluate the actual free acid value.
• Complementary acids. The best blends pair a deeper-penetrating acid (glycolic) with a gentler, hydrating acid (lactic) and possibly a pore-penetrating acid (salicylic or mandelic). Use the interaction checker to verify that the acids in your routine are safe to combine.
• Reasonable total concentration. Multi-acid does not mean multi-aggressive. Total AHA concentration of 5-10% is typical for effective daily-use blends.
• Evidence of testing. Products that cite clinical testing data (even brand-funded) show more commitment to efficacy than those relying purely on ingredient-level claims.

When Glycolic Acid Is the Clear Winner

Despite the appeal of gentler alternatives, glycolic acid remains the best-evidenced AHA for several specific applications:

Stubborn surface texture and roughness. No other AHA matches glycolic acid's resurfacing power at equivalent concentrations. The 2025 network meta-analysis confirmed its efficacy for reducing skin roughness [17].

Collagen stimulation. Bernstein et al. (2001) demonstrated that glycolic acid increases type I collagen mRNA and hyaluronic acid in human skin [7]. This finding has not been replicated with mandelic acid, tartaric acid, citric acid, or malic acid.

Hyperpigmentation in non-sensitive skin. For post-inflammatory hyperpigmentation and melasma in patients who tolerate it, glycolic acid has the most clinical evidence and outperforms lactic acid in head-to-head comparisons [13]. Glycolic acid also directly inhibits tyrosinase, the enzyme that produces melanin [10].

Acne treatment. Glycolic acid has robust RCT evidence for mild acne [8], systematic review support for chemical peels in acne [18], and demonstrated antibacterial activity against C. acnes [19]. No other AHA has this breadth of acne evidence.

When to Choose Another AHA

Sensitive skin: Start with mandelic acid or lactic acid. Their larger molecular sizes mean gentler, slower exfoliation with less acute irritation. See our skin types guide for detailed recommendations.

Very dry skin: Lactic acid's humectant properties make it the best AHA for dry skin. It exfoliates while drawing moisture into the skin - a combination glycolic acid cannot provide. See our glycolic vs lactic acid comparison.

Darker skin tones (Fitzpatrick IV-VI): Mandelic acid is often preferred as a first-line AHA because it carries less risk of triggering post-inflammatory hyperpigmentation [5]. Glycolic acid can be used safely in darker skin types but requires careful protocols and professional guidance [9].

Rosacea-prone skin: PHAs (gluconolactone, lactobionic acid) are the safest hydroxy acid choice for rosacea. Glycolic acid frequently triggers rosacea flares and should generally be avoided in this population.

Post-procedure recovery: PHAs provide gentle exfoliation without compromising the healing barrier. Glycolic acid should be avoided until the skin has fully recovered from procedures like laser treatment, microneedling, or medium-depth peels.

Frequently Asked Questions

Are all AHAs basically the same?

No. While all AHAs share the same fundamental mechanism (desmosome disruption in the stratum corneum), they differ meaningfully in molecular weight, penetration depth, irritation potential, and secondary properties (humectant, antioxidant, lipophilic). Choosing the right AHA for your skin type and concerns produces better outcomes than defaulting to the most popular option.

Is glycolic acid the "best" AHA?

Glycolic acid is the most potent and most studied AHA, with the strongest evidence for texture improvement, collagen stimulation, and hyperpigmentation treatment. But "best" depends on context. For sensitive skin, mandelic or lactic acid is "better" because glycolic acid's potency becomes a liability. For rosacea, PHAs are "better" because they exfoliate without triggering flares. The best AHA is the one that addresses your specific concerns without exceeding your skin's tolerance.

Can I mix different AHAs together?

Yes. Many products combine multiple AHAs, and this is a legitimate formulation strategy. The key is that the total acid load should be appropriate for your skin. Using a 10% glycolic acid serum and a 10% lactic acid toner in the same routine would be excessive for most people. But a well-formulated blend with modest concentrations of multiple acids can be effective and well-tolerated. Read more about how to use glycolic acid as part of a complete routine.

Do I need to worry about pH with all AHAs?

Yes. All AHAs follow the Henderson-Hasselbalch equation - the proportion of active (free, non-ionized) acid depends on the product's pH relative to the acid's pKa. The pKa values are similar across the AHA family (glycolic: 3.83, lactic: 3.86, mandelic: 3.41, citric: 3.13 for the first dissociation), so a product pH of 3.5-4.0 is effective for any of them [20]. Use the free acid calculator to compare actual potency.

References

1. 1. Sharad J (2013). Glycolic acid peel therapy - a current review. Clin Cosmet Investig Dermatolreview
2. 2. Van Scott EJ, Yu RJ (1974). Control of keratinization with alpha-hydroxy acids and related compounds. I. Topical treatment of ichthyotic disorders. Arch Dermatolclinical trial
3. 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 Resclinical trial
4. 4. Green BA, Yu RJ, Van Scott EJ (2009). Clinical and cosmeceutical uses of hydroxyacids. Clin Dermatolreview
5. 5. Sarkar R, Garg S, Bansal S, Sethi S (2012). Chemical peels for melasma in dark-skinned patients. J Cutan Aesthet Surgreview
6. 6. Garg VK, Sinha S, Sarkar R (2009). Glycolic acid peels versus salicylic-mandelic acid peels in active acne vulgaris and post-acne scarring and hyperpigmentation: a comparative study. Dermatol Surgcomparative study
7. 7. 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 Surgclinical trial
8. 8. 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 DermatolRCT
9. 9. Burns RL, Prevost-Blank PL, Lawry MA, et al. (1997). Glycolic acid peels for postinflammatory hyperpigmentation in black patients. A comparative study. Dermatol Surgclinical trial
10. 10. 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 Dermatolin vitro study
11. 11. 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 DermatolRCT
12. 12. Kim SJ, Park JH, Kim DH, Won YH, Maibach HI (1998). Increased in vivo collagen synthesis and in vitro cell proliferative effect of glycolic acid. Dermatol Surgclinical trial
13. 13. Indian J Dermatol (2025). 80% Lactic Acid Peel Versus 50% Glycolic Acid Peel for Melasma: A Randomised Clinical Trial. Indian J DermatolRCT
14. 14. Kaidbey K, Sutherland B, Bennett P, et al. (2003). Topical glycolic acid enhances photodamage by ultraviolet light. Photodermatol Photoimmunol Photomedclinical trial
15. 15. Decker A, Graber EM (2020). Two is better than one: the combined effects of glycolic acid and salicylic acid on acne-related disorders. J Cosmet Dermatolprospective study
16. 16. 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)RCT
17. 17. Sci Rep (2025). Comparative efficacy of topical interventions for facial photoaging: a network meta-analysis. Sci Repnetwork meta-analysis
18. 18. Castillo DE, Yousef K (2018). Chemical peels for acne vulgaris: a systematic review of randomised controlled trials. BMJ Evidence-Based Medicinesystematic review
19. 19. Yang AJ, et al. (2020). pH-Dependent Antibacterial Activity of Glycolic Acid: Implications for Anti-Acne Formulations. Sci Repin vitro study
20. 20. Decker LC, Graber EM (1996). Clinical and histological effects of glycolic acid at different concentrations and pH levels. Dermatol Surgclinical trial

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