Ketoconazole and Azelaic Acid as Scalp Adjuncts: Two Side Doors into the Hair Literature

Ketoconazole and azelaic acid reached compounded scalp solutions by different roads, and neither road began with hair. Ketoconazole is an azole antifungal whose 2% shampoo is an approved product for seborrhoeic dermatitis and dandruff, and it entered the hair literature through a 1998 report on long-term shampoo use in men with androgenic alopecia. Azelaic acid is a dicarboxylic acid with a long cosmetic and dermatological history, and it entered the hair literature through a 1988 in vitro study of 5-alpha-reductase in human skin. Both now appear in a four-ingredient compounded solution with minoxidil and finasteride, and a practice that sources that solution is well served by knowing how thin or thick the evidence for each ingredient is.

This article sets out what each molecule is, what the systematic reviews and the scalp-microbiome literature report for ketoconazole, what the azelaic acid literature contains and what it does not, where the guidelines place each, and what a compounded scalp solution is under section 503A. It attributes every finding to the study that reported it, makes no claim about what either ingredient does to hair, and leaves the prescribing decision with the prescriber.

Two ingredients that entered through the side door

An analogy that holds for the history and not for any effect is a house with a front door and a side door. Minoxidil and finasteride came through the front, with trials designed for hair and labels to match. Ketoconazole and azelaic acid came through the side, as an antifungal and a cosmetic acid whose hair rationales were noticed afterward, and a good deal of what is written about them in hair care still leans on that first observation rather than on a trial built for the question.

That describes where the literature is rather than criticising either molecule, and it is the reason the two systematic reviews below are worth reading in full rather than in summary.

Ketoconazole has shampoo studies, two systematic reviews, and a scalp-microbiome rationale

Piérard-Franchimont and colleagues reported in Dermatology in 1998 on long-term use of a 2% ketoconazole shampoo in men with androgenic alopecia, and described changes in hair density and in the proportion of follicles in the growth phase over the study period. Hugo Perez proposed ketoconazole as an adjunct to finasteride in a 2004 paper in Medical Hypotheses, which is a hypothesis paper rather than a trial and is cited here as the origin of the adjunct idea rather than as evidence for it.

Two systematic reviews took stock two decades later. Fields and colleagues reviewed topical ketoconazole for androgenetic alopecia in Dermatologic Therapy in 2020 and found seven eligible studies, two in animals and five in humans with 318 participants between them, and described the human evidence as limited and heterogeneous. Choi and colleagues reviewed topical ketoconazole across its dermatological applications in the Journal of Dermatological Treatment in 2019 and reached a similar reading for hair. Marks and colleagues, reviewing topical antiandrogen approaches in the American Journal of Clinical Dermatology in 2020, placed ketoconazole among the agents with a proposed local antiandrogen action and a small evidence base.

The more recent rationale is the scalp microbiome. Gupta and colleagues reviewed scalp microbiome alterations in androgenetic alopecia in the International Journal of Dermatology in 2026, Li and colleagues reviewed the scalp microbiome and hair axis in Research the same year, and Miao and colleagues reported a cross-sectional study of the follicle bacteriome and mycobiome in androgenetic alopecia in Clinical, Cosmetic and Investigational Dermatology. That literature describes associations between scalp microbial communities and pattern hair loss; it does not report a trial of an antifungal on that basis, and the distinction between an association and an intervention is the one to hold onto when reading it.

Azelaic acid has one enzyme study, a long cosmetic history, and no hair trial of its own

Stamatiadis and colleagues reported in the British Journal of Dermatology in 1988 that azelaic acid, and zinc, inhibited 5-alpha-reductase activity in human skin in vitro. That study is the whole of the mechanistic rationale for azelaic acid in a scalp solution, it is an in vitro finding, and it has been carried into combination formulations for more than three decades without a trial of azelaic acid for hair on its own.

The wider literature is about other things. Searle and colleagues reviewed the versatility of azelaic acid in dermatology in the Journal of Dermatological Treatment in 2022, and the review covers the approved gel and foam indications and the cosmetic uses that make the molecule familiar. Hair appears in that review as a proposed use rather than an established one, which matches the evidence.

Where the guidelines and the network analyses place each ingredient

The European S3 guideline by Kanti and colleagues in 2018 and the Japanese guideline by Manabe and colleagues, published in 2018 for the 2017 revision, both address ketoconazole at a lower recommendation grade than the approved actives, and the Japanese guideline in particular lists it among agents that may be considered with weak evidence. The 2025 Canadian consensus by Landells and colleagues restates the specialist approach with the approved actives at the centre. A 2024 systematic review of androgenetic alopecia management by Rosenthal and colleagues in the Journal of Cosmetic and Laser Therapy surveys the adjuncts in the same frame.

The 2025 network meta-analysis by Gupta and colleagues in the International Journal of Molecular Sciences compared conventional and non-conventional over-the-counter agents for male androgenetic alopecia on 24-week hair density and reported topical minoxidil 5% as the most effective of the agents compared. It is cited here for the frame it gives the adjuncts: whatever ketoconazole and azelaic acid contribute in a combination solution, the literature ranks the approved active they accompany far ahead of them.

What the compounded solution is, and what it is not

The compounded formulary lists a scalp solution of minoxidil 5% with azelaic acid 12.5%, finasteride 0.1% and ketoconazole 2%, and a ketoconazole 2% cream with niacinamide 4%. Both are prepared under section 503A of the Federal Food, Drug, and Cosmetic Act to an individual prescription, carry a beyond-use date rather than a shelf life, and have not been evaluated by the FDA for safety, effectiveness or quality, as the FDA’s own questions and answers on compounding state. The four-ingredient solution contains finasteride, so the FDA alert on compounded topical finasteride, discussed in full in the finasteride article of this series, applies to it.

Oral ketoconazole is a different product again and is not part of any scalp formulation on this site. The FDA limited the use of oral ketoconazole tablets in a 2013 drug safety communication on liver injury, drug interactions and adrenal effects, and that communication is cited here so a reader who searches the molecule’s name finds the oral warning attached to the oral product and not to the topical one.

Closing Observation

Ketoconazole and azelaic acid are the two ingredients in a compounded scalp solution whose evidence is oldest at its root and thinnest at its top. Ketoconazole has a 1998 shampoo study, two systematic reviews that describe the human evidence as limited, and a 2026 microbiome literature that describes associations rather than interventions. Azelaic acid has a single 1988 in vitro enzyme study and a dermatology review that lists hair as a proposed use. The guidelines place both below the approved actives, and the network analysis places the approved active they accompany far ahead of any adjunct.

What the literature does not support is the arithmetic the market performs next, in which four rationales are added up and presented as one result. A practice that reads each ingredient at its own level will understand what the four-ingredient solution contains and why, will keep the oral ketoconazole warning attached to the oral product, and will be considerably harder to sell a scalp solution to on the strength of a mechanism observed in a dish in 1988.