What percentage of azelaic acid actually works?

Azelaic acid is unusual among skin actives because it addresses acne, rosacea, and dark spots through distinct, parallel pathways — not a single trick repurposed across marketing claims. First: it kills Cutibacterium acnes by disrupting bacterial mitochondrial oxidoreductase enzymes; intracellular concentrations in bacteria accumulate to over 90-fold the ambient level. Second: it reduces inflammation by scavenging neutrophil-generated superoxide and hydroxyl radicals at sites of tissue injury — the same oxidative mechanism that drives rosacea flushing and PIH after breakouts. Third: it competitively inhibits tyrosinase (the rate-limiting enzyme in melanin production), with a selective preference for abnormal or hyperactive melanocytes over normal ones — meaning it fades pigmentation without bleaching adjacent healthy skin. Fourth: it normalizes follicular keratinization, reducing the microcomedone formation that seeds both acne and post-acne marks. These four mechanisms explain why the FDA has approved azelaic acid for two separate indications (rosacea and acne) and why dermatologists also use it off-label for PIH and melasma.

• Study Azelaic acid inhibits bacterial mitochondrial oxidoreductase enzymes essential for C. acnes respiration, with intracellular concentrations in bacteria reported to exceed ambient concentrations by over 90-fold. ¹
• Study Azelaic acid markedly decreases superoxide (O2-) and hydroxyl radical (OH.) generated by neutrophils, reducing oxidative tissue injury at inflammatory sites. ²
• Study Azelaic acid competitively inhibits tyrosinase and selectively inhibits hyperactive melanocyte proliferation and DNA synthesis without significantly affecting normal melanocytes, reducing the risk of hypopigmentation in adjacent healthy skin. ³
• Study Azelaic acid normalizes disturbed terminal differentiation of keratinocytes in the follicular infundibulum; intra- and interfollicular hyperkeratosis is significantly reduced or normalized after 8-12 weeks of twice-daily treatment. ¹⁰

15% is the FDA-approved prescription concentration for papulopustular rosacea, sold as Finacea Gel and Finacea Foam. This tier has the most robust RCT package for any concentration of azelaic acid. A phase 3 randomized, double-blind, vehicle-controlled trial of the 15% foam achieved a significantly greater IGA (Investigator Global Assessment) success rate versus vehicle at 12 weeks. In a head-to-head multicenter double-blind RCT of 251 patients with papulopustular rosacea, 15% azelaic acid gel was superior to 0.75% metronidazole gel — the most commonly prescribed rosacea antibiotic — in reducing mean inflammatory lesion count (-12.9 vs -10.7, p=0.003) at 15 weeks. For acne, a combined analysis of two double-blind comparative trials (n=580 total) showed 15% AzA gel achieved roughly 70% median reduction in inflammatory lesions — equivalent to 1% clindamycin gel and comparable in effectiveness to 5% benzoyl peroxide, but with fewer local side effects than BPO. The 15% concentration also has a meaningful PIH data point: a 16-week baseline-controlled study of 15% AzA gel documented significant reduction of both post-inflammatory hyperpigmentation and acne lesions simultaneously — relevant to patients on darker skin tones where acne and PIH are interlinked concerns.

• Study Finacea Foam 15% achieved a significantly greater IGA success rate versus vehicle at 12 weeks in a phase 3 randomized, double-blind, vehicle-controlled trial. ⁸
• Study 15% azelaic acid gel was superior to 0.75% metronidazole gel in reducing inflammatory rosacea lesions (-12.9 vs -10.7 mean lesion count change, p=0.003) at 15 weeks in a multicenter double-blind RCT of 251 patients. ⁹
• Study Azelaic acid 15% gel twice daily achieved approximately 70% median reduction in inflammatory lesions versus benzoyl peroxide 5% gel in 351 patients over 4 months and was equivalent to 1% clindamycin gel in 229 patients. ⁷
• Study A 16-week baseline-controlled study of azelaic acid 15% gel found significant improvements in both post-inflammatory hyperpigmentation and acne lesion count simultaneously. ⁶

20% is the FDA-approved prescription concentration for acne, sold as Azelex Cream (NDA 020428). It is also the concentration used in the landmark head-to-head melasma trials against hydroquinone. The pivotal comparison: a 24-week double-blind RCT of 329 women found 20% azelaic acid cream produced comparable outcomes to 4% hydroquinone cream for melasma (65% good/excellent results in both arms). A 2023 systematic review and meta-analysis of 6 RCTs (n=673) found azelaic acid produced a statistically lower mean MASI (Melasma Area and Severity Index) score change than hydroquinone (MD=-1.23, 95% CI -2.05 to -0.40, p=0.004), meaning hydroquinone edged ahead on average MASI reduction — but azelaic acid's side effect profile (no risk of ochronosis, no rebound hyperpigmentation, safe in pregnancy) makes it the preferred first-line option in several clinical guidelines when HQ is contraindicated. For acne, 20% concentrations have been used since the early regulatory submissions and are documented in the FDA label.

• Study A 24-week double-blind RCT of 329 women with melasma found 20% azelaic acid cream produced comparable results to 4% hydroquinone cream (65% good/excellent outcomes in both treatment arms). ⁴
• Study A 2023 systematic review and meta-analysis of 6 RCTs (n=673) found azelaic acid produced a statistically lower mean MASI score change than hydroquinone (MD=-1.23, 95% CI -2.05 to -0.40, p=0.004). ⁵
• Study Azelex (azelaic acid) cream 20% is FDA-approved for mild-to-moderate inflammatory acne vulgaris; systemic absorption after a single topical application is approximately 4% of the applied dose. ¹⁴

10% is the practical ceiling for non-prescription azelaic acid products in most markets (including the US and EU), and it is what The Ordinary's 10% Azelaic Acid Suspension and many other over-the-counter products contain. OTC products at this concentration often include penetration enhancers — dimethyl isosorbide is a common choice — to partially compensate for the lower active load. The evidence question is direct: no peer-reviewed RCT has tested a 10% azelaic acid formulation as a standalone controlled trial for any indication (acne, rosacea, PIH, or melasma). Every published clinical trial that demonstrated a therapeutic effect used either 15% or 20% Rx formulations. This is not evidence that 10% OTC is ineffective — azelaic acid does have measurable biological activity at sub-15% concentrations in mechanistic studies, and user-reported outcomes for mild PIH and redness are broadly positive. But the honest answer is that 10% OTC sits in an evidence gap: below the prescription concentrations where the RCT data lives, without its own controlled trial record.

One honest caveat No peer-reviewed RCT has independently tested a 10% OTC azelaic acid formulation head-to-head against 15% or 20% Rx concentrations for any indication. All clinical trial evidence — including every FDA-approved indication — comes from 15% or 20% prescription formulations. The 10% OTC tier is reasonably used for mild concerns and maintenance, but claims at this concentration should not be extrapolated from Rx trial data.

Azelaic acid is one of the very few topical actives that dermatologists and obstetricians broadly consider acceptable during pregnancy — retinoids are teratogenic and contraindicated; high-dose salicylic acid carries fetal risk warnings; oral antibiotics have gestational limits. Azelaic acid's safety case rests on three pillars: (1) approximately 4% of a topical dose is systemically absorbed, and even that small amount falls within the normal endogenous plasma range because azelaic acid is a naturally occurring molecule produced by skin flora and found in plasma in all individuals; (2) the CIR Expert Panel concluded that azelaic acid and its dicarboxylic acid derivatives are safe in present practices of use; and (3) a 2025 retrospective study of 197 pregnant patients found 20% azelaic acid was more effective than topical erythromycin or clindamycin for acne during pregnancy, with no difference in adverse effects across the three groups.

• CIR Azelaic acid and its cosmetically used derivatives are safe in present practices of use and concentration, per CIR Expert Panel review covering animal, clinical, and toxicological data. ¹³
• Study A 2025 retrospective study of 197 pregnant patients found 20% azelaic acid was more effective than topical erythromycin or clindamycin for acne, with no difference in adverse effects between groups. ¹¹
• Study Approximately 4% of a topical azelaic acid dose is systemically absorbed after a single application; plasma levels remain within the normal endogenous range, as azelaic acid is produced naturally by skin flora and found in plasma of all individuals. ¹⁴

What percentage of azelaic acid works for rosacea?

15% is the FDA-approved prescription concentration for papulopustular rosacea (Finacea Gel and Foam). A phase 3 randomized double-blind trial of Finacea Foam 15% showed a significantly greater IGA success rate versus vehicle at 12 weeks (PMID:26244354). In a head-to-head RCT of 251 patients, 15% AzA gel outperformed 0.75% metronidazole gel — the front-line rosacea antibiotic — in inflammatory lesion reduction at 15 weeks (PMID:15492198). OTC 10% products have user-reported benefit for mild redness but lack controlled trial data for rosacea at that percentage. ⁸⁹

What percentage of azelaic acid works for dark spots, PIH, and melasma?

The clinical trial evidence comes from 20% prescription formulations. A classic 24-week double-blind RCT (n=329 women) found 20% azelaic acid cream produced comparable results to 4% hydroquinone for melasma (PMID:1816137). A 2023 meta-analysis of 6 RCTs (n=673) confirmed hydroquinone produced a slightly greater average MASI reduction, but azelaic acid's safety profile — no ochronosis, no rebound hyperpigmentation, safe in pregnancy — makes it preferred when hydroquinone is contraindicated (PMID:37457606). For PIH combined with acne, 15% gel also has supporting data from a 16-week baseline-controlled study (PMID:21637899). ⁴⁵⁶

Is 10% OTC azelaic acid effective?

No independent peer-reviewed RCT has tested 10% azelaic acid specifically for any indication. All controlled clinical trial data — including both FDA-approved indications — comes from 15% (rosacea) or 20% (acne/melasma) prescription formulations. OTC 10% products typically add penetration enhancers (such as dimethyl isosorbide) to partially offset the lower concentration. For mild PIH and redness maintenance, 10% OTC is widely used with broadly positive anecdotal outcomes, but the evidence base does not extend to this concentration. For moderate-to-severe concerns, the prescription tier has the supporting data. ⁸⁷

Azelaic acid vs hydroquinone for melasma — which is better?

In head-to-head data, hydroquinone edges ahead on average MASI score reduction: a 2023 meta-analysis of 6 RCTs (n=673) found a statistically significant but modest advantage for hydroquinone (PMID:37457606). However, azelaic acid's tyrosinase inhibition is selective — it preferentially targets hyperactive melanocytes while sparing normal ones (PMID:2114832). Hydroquinone is non-selective and carries risks of ochronosis (paradoxical darkening with long-term use) and rebound hyperpigmentation on discontinuation. Azelaic acid is also safe in pregnancy; hydroquinone is not recommended. For many patients — especially those on darker skin tones, pregnant patients, or those who have failed or cannot tolerate hydroquinone — azelaic acid is the better clinical choice even if hydroquinone leads on a single aggregate metric. ⁵³⁴

Is azelaic acid safe during pregnancy?

Yes — it is one of the very few topical actives considered acceptable during pregnancy, when retinoids (teratogenic), high-dose salicylic acid, and many oral antibiotics are restricted. About 4% of a topical dose is absorbed systemically, and even that small amount falls within the normal endogenous range because azelaic acid is naturally produced by skin flora and present in plasma in all individuals (FDA:NDA020428). A 2025 retrospective study of 197 pregnant patients found 20% azelaic acid was more effective than topical erythromycin or clindamycin for pregnancy-related acne, with no difference in adverse effects between groups (PMID:40873252). Always confirm with a treating physician. ¹⁴¹¹¹³

Does azelaic acid need an acidic pH to work?

No — this is one of azelaic acid's formulation advantages over vitamin C. Azelaic acid is a non-ionizable dicarboxylic acid at physiological pH; it does not require a sub-3.5 pH for skin penetration. Marketed formulations range from approximately pH 3.5 to 5.5. The primary formulation challenge is solubility, not pH — azelaic acid is sparingly soluble in water (~2.4 g/L at 20°C), which is why prescription products use hydrogel, cream, or foam vehicles that suspend micronized particles, and why OTC suspensions (like The Ordinary's) need shaking before use. ¹²

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