Azelaic acid: the science behind clearer, calmer, more even skin

Science of Beauty Rx · Ingredient Library Evidence checked: 20 October 2026

Azelaic acid is unusually versatile: it can treat spots, reduce the bumps of rosacea and help fade uneven pigmentation. It does several jobs at once, rather than relying on a strong exfoliating effect.

It also makes azelaic acid easy to oversell. Treating rosacea bumps is different from removing visible blood vessels; improving brown acne marks is different from repairing scars. And a promising laboratory mechanism is not automatically the explanation for every clinical benefit. Here is how it works, what the evidence tells us, and what that means for your skin.

What is azelaic acid?

Azelaic acid has a short chain of nine carbon atoms, with an acid group at each end. Its chemical name is nonanedioic acid. Its structure is HOOC–(CH₂)₇–COOH: the chemical shorthand for that arrangement. Chemists call this a “dicarboxylic acid” because it has two acid groups. That does not mean it behaves like a stronger version of your usual exfoliating acid.¹

The molecule occurs naturally, including in some grains, and is also produced through fatty-acid metabolism. However, its natural occurrence tells us little about how well a finished product will work. Delivery into skin, concentration, tolerability and consistent application all matter.

Dermatological interest grew from research into the pale patches associated with pityriasis versicolor, a condition involving Malassezia yeasts. In 1978, Nazzaro-Porro and Passi investigated tyrosinase-inhibiting substances in yeast cultures, helping establish the connection between dicarboxylic acids and pigmentation. This was a starting point for research, rather than proof that one molecule fully explains the colour changes in that condition.²

Azelaic acid subsequently developed into a treatment for acne and inflammatory rosacea as well as a subject of pigmentation research. Its history helps explain its breadth: this is a pharmacologically active molecule with several targets, rather than simply another ingredient for polishing the skin surface.

Four ways azelaic acid works

Four actions of azelaic acid: reducing inflammatory signalling, suppressing acne-associated bacteria, normalising follicular keratinisation and reducing excess pigment formation. Molecular explanations are supported mainly by experimental research.

Figure 1. Four complementary actions. Clinical improvement is established for specific formulations and conditions; the contribution of each molecular mechanism in an individual patient remains uncertain. Original Science of Beauty Rx diagram.

1. Calming inflammation

Inflammation is part of the skin’s defence response, but too much can contribute to redness and inflamed spots. Immune cells release reactive molecules, called reactive oxygen species, which can damage surrounding tissue when produced in excess. Laboratory experiments found that azelaic acid reduced their production by neutrophils, a type of immune cell. This may help explain its calming effects.³

The distinction matters: an experiment showing reduced oxidative activity does not establish how much of a patient's improvement comes from that process. It also does not turn azelaic acid into a universal antioxidant treatment for ageing. Its clinical value should be judged by outcomes in the condition being treated.

2. Acting against acne-associated bacteria

Azelaic acid can inhibit acne-associated bacteria, including Cutibacterium acnes, previously called Propionibacterium acnes. Laboratory research suggests it can interfere with the processes bacteria use to function and grow. However, acne is not simply an infection: follicular blockage, sebum, inflammation and host responses also contribute.⁴

Azelaic acid is not a conventional topical antibiotic such as clindamycin. It therefore offers an option that does not depend on prolonged conventional antibiotic exposure. That is useful in acne care, but “antimicrobial” should not be translated into “sterilises the skin” or “balances every microbiome”. Nor does activity against bacteria establish that killing bacteria is how it treats rosacea.

3. Helping prevent blocked pores

Keratinocytes are the cells that form much of the epidermis and line the upper hair follicle. In acne, abnormal shedding and accumulation of these cells help create a plug: the beginning of a comedone, or blackhead/whitehead.

Azelaic acid helps regulate how these skin cells grow and mature, reducing the build-up that can block follicles. The practical result can be fewer blocked follicles alongside fewer inflamed lesions.⁵ “Anti-keratinisation” therefore means reducing abnormal follicular build-up, not removing keratin from otherwise healthy skin. Visible peeling is neither the aim nor a reliable measure of success.

4. Helping reduce excess pigment

Melanin is the pigment that gives skin its colour. Making it requires an enzyme called tyrosinase. In laboratory experiments, azelaic acid slows this enzyme’s activity; researchers have also found effects on other enzymes and processes inside cells.⁴ These findings provide a biological basis for treating hyperpigmentation, but laboratory concentrations and cellular effects cannot be transferred directly to a skincare routine.

Azelaic acid is often described as preferentially affecting unusually active pigment-producing cells. That is a useful shorthand, not a targeting system that recognises every dark patch. The treatment aims to improve excess pigmentation, rather than erase normal skin colour. Irritation can itself worsen pigmentation, so tolerability remains part of pigment treatment, particularly in skin prone to persistent dark marks.

Rosacea: the KLK5–cathelicidin–LL-37 pathway

In rosacea, the skin’s rapid-response defence system can become overactive. Blood vessels, nerves and environmental triggers also play a part. One important research pathway involves kallikrein 5 (KLK5), a protein-cutting enzyme, and cathelicidin, an antimicrobial defence protein.

The skin makes a defence protein called hCAP18. KLK5 helps cut it into smaller pieces, including LL-37, which normally helps protect the skin. In rosacea, too much protein-cutting activity and changes in the resulting pieces may encourage inflammation. Studies of human skin and experiments in mice support this connection.⁶

KLK5 processes the cathelicidin precursor hCAP18 into LL-37 and related peptides. Dysregulated processing can promote inflammation and vascular responses. Azelaic acid is associated with reduced KLK5 and cathelicidin expression and reduced protease activity, but its exact clinical mediation is unproven.

Figure 2. A simplified rosacea pathway. Solid arrows show processing and downstream biology; dashed arrows show changes associated with azelaic acid exposure. This is one part of rosacea biology, not a complete disease model. Original Science of Beauty Rx diagram.

A 2013 study combined laboratory experiments with 16 weeks of treatment in people with rosacea. During treatment with azelaic acid 15% gel, researchers found reduced activity in the genes that produce KLK5 and cathelicidin, alongside changes in protein-cutting enzyme activity.⁷

There are important limits. The patient study was small, and everyone knew which treatment they were using. It did not include a comparison group using the gel base alone. It therefore could not show that these biological changes caused the improvement, or predict who would respond. Turning down the gene that produces KLK5 also does not prove that azelaic acid directly blocks the enzyme itself. The defensible wording is that azelaic acid may help regulate this pathway; describing it as a proven, selective “LL-37 blocker” goes beyond the evidence.

What can azelaic acid help with?

Acne: an established treatment

Azelaic acid can improve red bumps and pus-filled spots, as well as blackheads and whiteheads. Its combination of actions is particularly relevant when active acne and brown residual marks coexist. However, it should not delay assessment of deep nodules, developing scars or acne causing substantial distress.

A Cochrane review found that azelaic acid probably produced a poorer patient-rated acne response than benzoyl peroxide, while probably making little or no difference compared with tretinoin for that outcome. Many other comparisons had low or very low certainty because studies were small or at risk of bias.⁸ Neither “as effective as every retinoid” nor “too weak to treat acne” captures that evidence.

UK NICE NG198 includes topical azelaic acid with oral doxycycline or lymecycline among initial options for moderate-to-severe acne. It also permits azelaic acid as a maintenance alternative when adapalene/benzoyl peroxide is not tolerated or a component is contraindicated. NICE's treatment framework uses 12-week courses and review; azelaic acid is not its universal first choice for every mild breakout.⁹

Rosacea bumps and pustules: strong evidence

This is the clearest rosacea indication: raised red bumps and pustules, usually against a background of facial redness. Two randomised, double-blind, vehicle-controlled trials enrolled 664 participants. Mean inflammatory lesion reductions were 58% versus 40% in one trial and 51% versus 39% in the other, favouring azelaic acid 15% gel.¹⁰

Those figures show that the active treatment helped, but people using the gel base alone also improved. They are average reductions in lesion counts, not the percentage of people cured. Rosacea is usually a chronic condition requiring ongoing management.

Redness accompanying inflammatory disease may improve, but persistent flushing and visible thread veins are different treatment targets. Studies have not shown a meaningful effect on visible thread veins, also called telangiectasia.¹¹ Azelaic acid is therefore a reasonable treatment for inflammatory rosacea, not a complete answer to every red face.

Dark marks after spots: promising evidence

Post-inflammatory hyperpigmentation (PIH) means excess pigment left after inflammation—for example, flat brown marks after acne. It differs from post-inflammatory erythema, which is predominantly a residual red or pink vascular change, and from depressed or raised scars.

A 2024 randomised, double-blind, placebo-controlled study enrolled 72 people with acne; 60 completed treatment. It reported benefits across measures of acne-related marks, including reduced melanin content in azelaic-acid-treated PIH lesions at week 12. Both groups improved on some PIH measures, and the trial was registered after it had taken place, which makes it harder to check which outcomes were planned in advance.¹²

This supports potential benefit without establishing a guaranteed clearing time, equal effectiveness across all skin tones or superiority over every alternative. Controlling new acne matters too: repeatedly creating new inflammation makes existing pigmentation harder to judge. Azelaic acid can address the trigger and the aftermath, but does not rebuild indented scars.

Melasma: a useful option, with limits

Melasma causes acquired, often symmetrical facial pigmentation and commonly relapses. A 24-week study of 329 women, in which neither participants nor assessors knew which treatment each person received, compared azelaic acid 20% with hydroquinone 4%, alongside broad-spectrum sunscreen. It found no significant overall treatment difference on the reported assessments.¹³

That finding supports azelaic acid as an option; it does not prove universal equivalence. Results depend on the comparator, formulation, assessment method and population. Melasma often needs an individual plan, and improvement while using treatment does not establish permanent clearance.

Light protection is a foundation of pigment management. For melasma, discuss protection against visible light as well as ultraviolet exposure, including appropriately tinted sunscreen containing iron oxides.²¹ Evidence for pigmentation is meaningful, but less extensive and consistent than the inflammatory rosacea evidence. In the UK, treating melasma or PIH with these named medicines is outside their licensed indications.

Azelaic acid versus other familiar actives

These ingredients overlap, but they are not interchangeable. Choose according to the diagnosis, treatment goal and what the skin can tolerate.

Ingredient	Main practical role	How the choice differs from azelaic acid
Salicylic acid	A keratolytic commonly used for congestion and comedones	It helps loosen accumulated surface/follicular cells. Evidence for specific acne regimens is limited; it does not have azelaic acid's established inflammatory rosacea indication.
Benzoyl peroxide	An antibacterial acne treatment, often used in combinations	It has stronger comparative evidence for some acne outcomes and an important role alongside antibiotics. It can irritate and bleach fabrics.
Topical retinoids, including adapalene and tretinoin	Regulating follicular cell turnover and treating/preventing acne lesions	They are central to many acne regimens, but often irritate initially and are contraindicated during pregnancy and pregnancy planning. Cosmetic retinol is not an interchangeable substitute.
Azelaic acid	Acne, inflammatory rosacea and selected pigment concerns	It offers overlapping benefits without being a retinoid or conventional antibiotic, but can still cause substantial stinging.

The comparative evidence does not justify a single winner for everyone.^8,9 Combining treatments may help acne, but adding several irritating products at once makes it harder to identify what is working. Rosacea skin generally needs an especially restrained routine.

UK formulations: why 10%, 15% and 20% are not a ladder

10% skincare products are available without prescription, but cannot be assumed to reproduce results from medicinal 15% or 20% formulations. Check that the ingredient is azelaic acid: a derivative such as potassium azeloyl diglycinate is a different substance, and its percentage is not directly interchangeable.

Finacea 15% gel is a prescription-only medicine licensed for mild-to-moderate facial papulopustular acne and papulopustular rosacea. Skinoren 20% cream is prescription-only and licensed for acne vulgaris.^14,15 Concentration alone neither defines a product's regulatory status nor establishes its indication.

The vehicle—the gel, cream or suspension carrying the ingredient—controls how the molecule dissolves, leaves the formulation and enters skin. Experimental delivery research demonstrates strong vehicle and pH effects, although animal-skin experiments cannot directly rank clinical products.¹⁶ A higher percentage therefore does not automatically mean greater benefit, and a lower percentage does not automatically mean less irritation.

Texture, excipients and adherence also matter. The most effective formulation on paper is unhelpful if discomfort means it is rarely applied. Avoid treating “15% gel beats 20% cream” as a universal rule: different indications and formulations require their own evidence.

How to use it, and when to reassess

Follow the instructions for the exact product and the prescriber's plan. Both named medicines normally use twice-daily application; about 0.5 g, a 2.5 cm strip, covers the face. Skinoren advises once-daily evening use for the first week in sensitive skin. Reduce frequency or briefly pause if irritation develops.^14,15

A practical routine is gentle cleansing, drying, a thin application over the affected area, and a simple moisturiser. Apply sunscreen in the morning. Moisturiser can improve comfort; a human-skin laboratory study found no major change in absorption when the tested moisturisers were applied before or after 15% gel. That result does not validate every possible product combination.¹⁷

Introduce other actives cautiously. There is no need to chase a tingling sensation, scrub away flakes or apply a thicker layer to accelerate results. For rosacea, avoid abrasive or peeling products that provoke irritation.

Meaningful change takes weeks. Finacea's SmPC advises stopping and considering alternatives if acne has not improved after one month, or rosacea after two months, or either worsens. These product-specific instructions should not be overridden by NICE's broader 12-week acne review framework.¹⁴ Pigment studies commonly assess outcomes over several months; persistent marks are not evidence that extra applications will work faster.

Adverse effects and pregnancy

Burning, stinging, itching and dryness are the main practical problems; local redness and peeling may occur. Mild initial discomfort can settle, but persistent painful irritation needs reassessment. New pale patches also warrant advice. Rare hypersensitivity reactions and worsening asthma have been reported. Stop and seek urgent help for facial swelling or breathing difficulty. Keep treatment away from eyes and mucous membranes.^11,15

Azelaic acid is commonly considered a useful option during pregnancy and breastfeeding because only a small amount reaches the bloodstream. Clinical reviews support its use, but good-quality trials in pregnant people are lacking: “commonly acceptable” is more accurate than “proven completely risk-free”.¹⁸ A small human absorption study estimated absorption of 3.6% of an applied 20% cream dose; that figure is not a universal absorption rate for every formula or skin condition.¹⁹

Both UK SmPCs advise caution in pregnancy and breastfeeding, and babies must not contact treated skin or breasts.^14,15 Discuss use with a pharmacist or prescriber; avoid application to the nipple or breast. LactMed considers topical use low risk and says necessary treatment is not a reason to stop breastfeeding.²⁰

Misconceptions worth leaving behind

“It is just a gentle exfoliant.” Its effects extend beyond follicular cell build-up, and “gentle” does not guarantee comfort.

“Stinging proves it is working.” Sensation is not an efficacy test. A comfortable routine can still be effective.

“Every flare is purging.” Worsening may reflect irritation, an unsuitable formulation or uncontrolled disease. Do not automatically push through it.

“It removes all redness and scars.” Inflammatory lesions, vascular redness, pigment and structural scarring are different problems.

“Natural means pregnancy safety is guaranteed.” Decisions depend on exposure and clinical evidence, not the ingredient's origin.

Azelaic acid can be especially useful when you want to address more than one concern: acne with residual brown marks, or papulopustular rosacea where a treatment applied to the skin is suitable and a conventional antibiotic is not needed. Choose a formula suited to the condition, build a routine your skin can tolerate, and be clear about the change you hope to see. Persistent inflammation, scarring or an uncertain diagnosis calls for clinical review rather than an ever more complicated skincare shelf.