How does azelaic acid work on acne?

The short answer: several actions, none proven in people

Azelaic acid is a naturally occurring nine-carbon acid, and it is usually described as doing several things at once: antibacterial, anti-keratinizing, and anti-inflammatory. A mechanism review lays out these effects, but we did not find a current AAD, FDA, or NIH statement that spells out how it works in acne.

Treat the explanation below as a best synthesis rather than settled fact. Most of it rests on lab work, with thinner support from people.

Bacteria: slowing them down rather than wiping them out

This is the best-supported part. Azelaic acid appears to inhibit bacterial enzymes needed for respiration and protein synthesis, and in lab work that slows growth of Cutibacterium acnes and other Gram-positive skin bacteria. A pharmacology review describes this as bacteriostatic, meaning it holds bacteria in check without eradicating them at therapeutic concentrations.

That distinction matters. The same review suggests a holding-pattern approach may carry a lower resistance risk than antibiotics, though that is an inference rather than a measured result. Activity also seems stronger in mildly acidic conditions, like acne-affected skin, but that comes mainly from laboratory studies.

Inflammation and the skin microbiome

Azelaic acid also seems to calm inflammation. One review reports that it downregulates pro-inflammatory signals including interleukin-1 beta and tumor necrosis factor-alpha, both tied to the redness and swelling of inflamed lesions.

The same mechanism review describes a small microbiome study: 55 patients applied a 15% gel daily for 28 days. Microbial diversity at acne sites improved, bacterial and staphylococcal populations dipped slightly, and lactobacilli rose significantly. Twenty-eight days and 55 people is a thin base, so we read it as a clue, not proof.

Keratin and clogged pores: the weakest link

MedlinePlus, the National Library of Medicine's drug guide, describes the drug as killing the bacteria behind acne and decreasing keratin production. It also says the drug helps keep pores clean. That keratin claim is the least well-supported part of the account, and we found no strong human data confirming it.

How well it works in practice

Bottom line: it outperforms vehicle in several trials and looks roughly comparable to benzoyl peroxide and clindamycin in older head-to-head work, but the evidence is small and mostly short.

A 2023 systematic review of 43 randomized trials across acne, rosacea, melasma, and aging found sixteen acne studies suggesting azelaic acid beats vehicle on global assessment and lesion severity. The 20% strength also cleared more lesions than erythromycin gel. The review required trials of at least six weeks.

In a 2004 report of two blinded trials, 15% gel matched 5% benzoyl peroxide and 1% clindamycin on inflamed lesions, with median reductions of about 70 and 71 percent. That is an older report, so we would not rely on it alone. (Gollnick et al., 2004)

Other evidence is mixed. A network meta-analysis found the monotherapy effect versus placebo had a credible interval crossing zero, while the combination with clindamycin looked stronger. A systematic review notes that a 1997 trial favored 3% erythromycin with 5% benzoyl peroxide over 20% azelaic acid on inflammatory lesions.

A review of azelaic acid uses summarizes a 2015 study of 55 patients in which 15% gel twice daily for nine months beat a three-month course of the same gel and 0.1% adapalene for six months on inflammatory lesions. We could only check that through the summary, not the original paper.