IngredientsUndecylenic acid, also known as undecenoic acid, is an organic compound with the molecular formula CH2=CH(CH2)8CO2H and is classified as an unsaturated fatty acid. Its systematic chemical name is 10-undecenoic acid, with the structural shorthand CH2=CH(CH2)8COOH. It is an 11-carbon monounsaturated fatty acid (C11:1). Other synonyms documented in the scientific literature include undec-10-enoic acid, 10-hendecenoic acid, 10-henedecenoic acid, n-undecylenic acid, and undecenoic acid; it has also appeared under the trade names Desenex, Declid, Renselin, and Sevinon.
Salts and esters of undecylenic acid are collectively known as undecylenates. Pharmacologically recognized undecylenate salts include calcium undecylenate, copper undecylenate, and zinc undecylenate, which are topical antifungal agents typically used in combination, with the combined potency labeled in terms of total undecylenate content. The combination of zinc undecylenate and undecylenic acid is sometimes referred to as zincundecate.
Undecylenic acid is a colorless oil at room temperature. Chemically, it is an unsaturated fatty acid with the molecular formula C11H20O2, and it features a terminal double bond between the 10th and 11th carbon atoms. The presence of this terminal double bond imparts unique chemical properties that influence undecylenic acid's interaction with microbial cell membranes. The compound is bifunctional in nature, possessing both a terminal olefinic group and a carboxylic acid group, which together enable its wide range of chemical and biological activities.
Castor oil is a non-edible oil extracted from the seeds of the castor bean plant Ricinus communis (Euphorbiaceae), which grows in tropical and subtropical areas. Globally, around one million tons of castor seeds are produced every year, with the leading producing areas being India, China, and Brazil. 10-Undecenoic acid (undecylenic acid) is a fatty acid derived from castor oil. Undecylenic acid is also naturally found in human sweat. Undecylenic acid, present in sweat, is a potent antifungal that forms part of the body's natural antimicrobial defense. It has additionally been reported as a metabolite in Rhodotorula glutinis var. lusitanica and is found naturally occurring in the essential oils of Juniperus chinensis, Thujopsis dolabrata, and in skim milk powder.
Undecylenic acid is prepared industrially by pyrolysis of ricinoleic acid, which is derived from castor oil. Specifically, the methyl ester of ricinoleic acid is cracked to yield both undecylenic acid and heptanal. The process is conducted at 500–600 °C in the presence of steam, after which the methyl ester is hydrolyzed.
As a pharmaceutical and supplement ingredient, undecylenic acid is available as an ointment, powder, or liquid. It is found in over-the-counter (OTC) antifungal preparations most commonly as the free acid or as zinc, calcium, or copper undecylenate salts. It is used in the manufacture of pharmaceuticals, cosmetics, and perfumery, including antidandruff shampoos, antimicrobial powders, and as a musk in perfumes and aromas. As an oral supplement, it has historically been prepared in softgel or gelcap form (encapsulated in fish gelatin capsules) for internal use.
The therapeutic efficacy of undecylenic acid was first recognized in the 1940s in treating superficial fungal diseases affecting military troops. Shapiro and Rothman reported their research on undecylenic acid in the treatment of dermatomycosis in 1945, when the United States was engaged in World War II; cutaneous diseases, including fungal infections, were a major cause of disability during the conflict.
During World War II, soldiers experienced a significant problem due to fungal infections including various mycoses, athlete's foot, aspergillosis, and candidiasis; communal bathing, inadequate hygiene, and poor sanitation helped in spreading infections. Military researchers evaluated undecylenic acid powder extensively as a preventive and therapeutic intervention. The powders tested included undecylenic acid powder in various formulas; the strongest formulation used contained zinc undecylenate in talc. The standard foot powder of the era (as of 1956) contained either undecylenic acid 2% and zinc undecylenate 20%, or an alternative calcium propionate/zinc caprylate/zinc propionate combination.
In controlled field trials, active fungal infections developed in 8.85% of 260 men who received no treatment, in 11.16% of 251 men who used boric acid-salicylic acid powder, in 3.10% of 258 men who used propionate powder, and in only 1.07% of 281 men who used undecylenic acid-undecylenate powder. These observations indicated that undecylenic acid powder afforded a superior degree of protection against fungal infections compared to the other agents tested. In both prophylactic and therapeutic trials, undecylenic acid powder showed significant superiority to all other fungistatic agents tested.
Following the war, pharmaceutical companies recognized undecylenic acid's broader value, incorporating it into creams and powders available to the general public.
The antifungal properties of fatty acids broadly, and undecylenic acid specifically, were subjects of scientific interest as early as the late 1930s, with investigators such as Hoffman, Schweitzer, and Dalby documenting their fungistatic properties in the scientific literature (1939), and Peck and Rosenfeld studying the effects of fatty acids on fungal growth (1938). These early investigations laid the theoretical groundwork for the wartime clinical applications that followed. Early dermatological preparations included ointments intended for tinea pedis (athlete's foot) and other dermatomycoses, typically applied to the affected skin. Undecylenic acid's use in this context represented one of the first systematic applications of a fatty acid-based antifungal in modern medicine.
Beginning in the latter decades of the twentieth century, undecylenic acid became incorporated into complementary and alternative medicine frameworks, particularly for the management of intestinal Candida overgrowth. A 1954 publication by Neuhauser in a medical journal reported on the treatment of intestinal candidiasis with undecylenic acid preparations taken internally. In the alternative medicine community, oral supplement formulations were developed and commercialized during the 1980s and 1990s for this purpose. The Alternative Medicine Review published a clinical monograph on undecylenic acid in 2002 (PMID 11896747), providing a comprehensive summary of the evidence available at that time for both topical and internal applications.
Undecylenic acid is an 11-carbon monounsaturated fatty acid (MUFA) derived from the distillation of castor oil via pyrolysis. The active molecule in all preparations — whether as the free acid, as a zinc, calcium, or copper salt, or as an ester such as glyceryl undecylenate — is 10-undecenoic acid (C11:1). The unique chemical structure of undecylenic acid, characterized by the presence of a terminal double bond and a carboxylic acid group, is central to its bioactivity.
The mechanism of action and effectiveness in fatty acid-type antifungals is dependent on the number of carbon atoms in the chain, with efficacy increasing with the number of atoms in the chain. The optimum appears to be 11 carbon atoms; with longer fatty acids, the antifungal effect is limited by lower solubility in water, which results in reduced bioavailability. This chain-length optimization is why undecylenic acid (C11) is more potent as an antifungal than, for example, caprylic acid (C8).
In terms of the mechanism underlying its antifungal effects against Candida albicans, undecylenic acid inhibits morphogenesis. In a study on denture liners, undecylenic acid was found to inhibit conversion of yeast to the hyphal form (which is associated with active infection) via inhibition of fatty acid biosynthesis.
A 2016 laboratory study published in the International Journal of Clinical Pharmacology and Therapeutics (Shi et al.) investigated the antifungal mechanisms of undecylenic acid in detail. Hyphal growth of Candida albicans and biofilm formation have been well recognized as important virulence factors for the initiation of skin infection and the later development of disseminated infection. The study found that undecylenic acid inhibits biofilm formation of C. albicans effectively at concentrations above 3 mM; at concentrations above 4 mM, the morphological transition from yeast to filamentous phase is abolished; meanwhile, the cell surface is crumpled, and cells display an atrophic appearance under scanning electron microscopy even at low drug concentrations. Furthermore, the drug treatment decreases the transcriptions of hydrolytic enzymes such as secreted aspartic protease, lipase, and phospholipase; hyphal formation-related genes such as HWP1 are also significantly reduced at the transcriptional level in drug-treated biofilm conditions.
A broader mechanistic review published in Mycopathologia (Rossi et al., 2021) characterized the mechanism further: Recent advances indicate that the toxic effect of undecanoic acid involves modulation of fungal metabolism through its effects on the expression of fungal genes that are critical for virulence. Specifically, the compound triggers oxidative stress, leading to changes in fatty acid, phospholipid, and ergosterol synthesis; increased levels of reactive oxygen species (ROS) cause damage to the cell membrane and cell wall; additionally, the compound decreases the expression and activity of proteases and induces alternative splicing in genes involved in several cellular processes.
Fluorescence microscopy experiments have revealed that an arginine undecylenate salt (GS-1) elicits antibacterial activity by rapidly permeabilizing bacterial membranes and inducing reactive oxygen species formation. Fatty acids broadly have long shown potential as novel antimicrobials, but their development has been limited by solubility and efficacy concerns in topical applications.
A novel formulation of undecylenic acid compounded with L-arginine, designated GS-1, was found to induce concentration-dependent tumor cell death; further investigation revealed that GS-1-mediated cell death was caspase-dependent with a reduction in mitochondrial membrane potential, suggesting a pro-apoptotic mechanism of action. Like other fatty acids studied previously, GS-1 was found to localize to lipid droplets after entering tumor cells via Fatty Acid Transport Protein 2 (FATP2). These findings are entirely preclinical (in vitro) and have not been tested in human subjects.
Regulatory Status: Undecylenic acid is defined as a natural fungicide approved by the U.S. Food and Drug Administration for use in over-the-counter medications that treat skin disorders. Undecylenic acid and its salts of calcium, copper, and zinc, at a total undecylenate concentration of 10–25%, are included in the FDA's Final OTC Antifungal Monograph (M005), alongside tolnaftate, clotrimazole, and miconazole nitrate. Undecylenic acid is approved by the U.S. FDA for topical route and is listed in the Code of Federal Regulations.
Clinical Evidence — Placebo-Controlled Trials: In a systematic review of topical treatments for fungal infections of the foot, undecanoates (undecylenic acid and zinc undecylenic acid) were compared with placebo in two randomized controlled trials (n = 125; Chretien 1980; Fuerst 1980), and a statistically significant relative reduction in treatment failure of 71% was found (Risk Ratio 0.29, 95% CI 0.12 to 0.70), with at least 80% follow-up maintained in both trials.
Comparative Efficacy: In a review of placebo-controlled trials, undecenoic acid was deemed efficacious alongside prescription azoles (e.g., clotrimazole) and allylamines (e.g., terbinafine). However, undecylenic acid has little efficacy when compared with newer antifungal agents. The advantages of these compounds are that they are safe, inexpensive, and rarely cause local irritation.
Evidence Strength: Moderate for tinea pedis and tinea corporis in the context of OTC self-treatment, based on two RCTs (total n = 125) showing statistically significant efficacy vs. placebo. Undecylenic acid is less effective than newer azole and allylamine antifungals in head-to-head comparisons.
In Vitro Evidence: The antifungal effects of undecylenic acid have been extensively investigated in Candida albicans, where studies have shown that it can inhibit biofilm formation. The 2016 in vitro study (Shi et al., Int J Clin Pharmacol Ther, 54:343–353) established that undecylenic acid inhibits C. albicans biofilm formation at concentrations above 3 mM and abolishes the yeast-to-hyphal morphological transition at concentrations above 4 mM. An additional study of undecylenic acid-impregnated polymer composites (PMMA-UA composites, 2018) found that as-prepared composites with ≥6% undecylenic acid reduced sessile Candida by over 90%, and after six days the composites were still efficiently reducing sessile Candida cells by approximately 70%.
Oral/Intestinal Candida: An early clinical observation published in 1954 by Neuhauser reported successful outcomes in treating intestinal candidiasis with oral undecylenic acid preparations, but this was a single, non-controlled case series of limited methodological quality. No subsequent rigorously designed randomized controlled trials of oral undecylenic acid supplementation for intestinal candidiasis have been published in the peer-reviewed literature. Claims regarding oral use for "Candida overgrowth" in the modern supplement context are therefore based on very limited human evidence and primarily extrapolated from in vitro and historical case-based data.
Evidence Strength: Strong in vitro evidence for anti-biofilm and anti-morphogenetic effects in C. albicans; human clinical evidence for intestinal applications is very weak (single historical case series).
A 2025 study published in Experimental Dermatology (Mayfosh and Rau) investigated an ammonium carboxylate salt of undecylenic acid (arginine undecylenate; GS-1) for the topical treatment of Gram-positive and antibiotic-resistant skin infections. The investigators found that combining the amino acid L-arginine with undecylenic acid produced a water-soluble salt that showed effective antibacterial activity against clinical isolates of methicillin-sensitive S. aureus (MSSA), methicillin-resistant S. aureus (MRSA), vancomycin-intermediate S. aureus, and S. pyogenes, with MICs of 0.60–1.26 mg/mL and MBCs of 0.63–5.04 mg/mL. Serial exposure of 5 MRSA clinical isolates to sub-lethal doses of GS-1 did not appear to induce resistance; compared to mupirocin, repeated exposures to GS-1 appeared to sensitize bacteria to GS-1; in an animal model of skin infection, topical GS-1 successfully eradicated MRSA from infected, abraded skin after 6 days of treatment with no signs of toxicity; and in a repeated topical exposure study in humans, GS-1 caused no irritation or sensitization.
A separate in vitro study (Startseva et al., published in Ukrainian Biochemical Journal) confirmed that undecylenic acid demonstrated antibacterial potential at 2.5 and 5.0 μM concentration against both gram-positive bacteria (S. aureus) and gram-negative (E. coli) cultures, confirmed by monitoring the diameter of bacterial growth inhibition zones.
Evidence Strength: Preclinical (in vitro and animal model) evidence for antibacterial activity is promising, particularly for the arginine undecylenate salt formulation. Human skin exposure data for GS-1 indicated no irritation or sensitization. No randomized controlled trials in humans for antibacterial indications have been completed.
A 2022 study published in the International Journal of Molecular Sciences (Day et al., Monash/La Trobe Universities) explored undecylenic acid's potential in oncology. Undecylenic acid is currently in clinical use as a topical antifungal agent; however, the potential for therapeutic application in other disease settings had not previously been investigated. The study described a novel platform for the solubilization of fatty acids using amino acids and used this approach to define a tumoricidal activity and underlying mechanism for undecylenic acid. The novel formulation GS-1 induced apoptotic cancer cell death with undecylenic acid being the cytotoxic component; the data suggested that GS-1-mediated cell death was caspase-dependent and resulted in typical apoptotic cell morphologies and a reduction in mitochondrial membrane potential.
The study demonstrated that GS-1 has effective pro-apoptotic antitumor activity in vitro, and together with the novel platform of fatty acid solubilization, contributes to the re-emerging field of fatty acids as potential anti-cancer therapeutics.
Evidence Strength: Entirely preliminary, in vitro only. No human or animal cancer studies have been conducted. This line of research is exploratory and not a basis for therapeutic claims.
Undecylenic acid is a precursor to active ingredients in antidandruff shampoos and antimicrobial powders. Its use in antidandruff formulations is based on its recognized antifungal activity against the Malassezia species implicated in dandruff and seborrheic dermatitis. When used for tinea cruris, undecylenic acid can result in extreme burning; in some case studies of tinea versicolor, pain and burning have also been reported following fungicide application.
Evidence Strength: Use in antidandruff products is long-established as an ingredient in commercial formulations, but formal clinical trial data specifically for undecylenic acid in tinea versicolor or seborrheic dermatitis are limited.
Research into incorporating undecylenic acid into dental materials has progressed as a strategy to prevent oral candidiasis associated with denture use. Due to growing issues with fungal infections, especially with Candida, there is a recognized need to develop novel anti-Candida materials; undecylenic acid is a known antifungal agent, but its oily nature and limited solubility have restricted its direct application. Studies have explored formulations including hexosome emulsions and PMMA-UA composites. In the hexosome study (Mionić Ebersold et al., Nanomaterials, 2018): the minimal inhibitory concentration for 50% and 90% Candida growth reduction was found at 0.01 and 0.16 wt% hexosomes, respectively.
Evidence Strength: Preclinical (in vitro and materials science studies). No human randomized controlled trials for undecylenic acid-embedded dental materials have been published.
Undecylenic acid and undecylenate salts are used individually or in combination in total concentrations of 10–25%. Preparations containing the drugs are applied topically twice daily after cleansing the affected area. The ointment form is typically recommended for use at night.
The FDA Final OTC Antifungal Monograph specifies the allowable concentration range: undecylenic acid and its calcium, copper, and zinc salts, combined, at a total undecylenate concentration of 10–25%. OTC label data confirm that products may be formulated at concentrations such as 10% (cream) or 25% (liquid solution). Duration of treatment typically specified in product labeling is up to 4 weeks for athlete's foot and ringworm, and up to 2 weeks for jock itch.
Research studies on Candida albicans biofilm inhibition found optimal inhibitory concentration above 3 mM, with complete abolition of yeast-to-filamentous phase morphological transition at concentrations above 4 mM.
For the arginine undecylenate (GS-1) antibacterial formulation, minimum inhibitory concentrations (MICs) against gram-positive pathogens including MSSA, MRSA, and S. pyogenes ranged from 0.60 to 1.26 mg/mL, and minimum bactericidal concentrations (MBCs) ranged from 0.63 to 5.04 mg/mL.
Oral supplementation with undecylenic acid (typically in softgel capsules) has been commercially available, with a product formulation referenced in the Alternative Medicine Review monograph (2002) suggesting specific gelcap dosing. However, no rigorously conducted dose-ranging or efficacy studies for oral undecylenic acid supplementation in humans have been published in the peer-reviewed literature, so no specific validated oral dosage can be cited.
The advantages of undecylenic acid-based compounds include that they are safe, inexpensive, and rarely cause local irritation. When used for tinea cruris, it can result in extreme burning. In some case studies of tinea versicolor, pain and burning result from fungicide application.
In a human repeated topical exposure study using the arginine undecylenate (GS-1) salt formulation, repeated topical exposure caused no irritation or sensitization. The free acid in higher concentrations, however, may produce more skin irritation than its salts.
FDA drug interaction databases record zero contraindications, zero severe interactions, and zero moderate drug interactions for undecylenic acid when used topically. There is minimal information on systemic drug interactions with undecylenic acid due to its predominant topical application.
OTC product labeling specifies that undecylenic acid preparations should not be used on children under 2 years of age except under the direction of a physician.
Fatty acids such as undecylenic acid are almost completely water insoluble and must be combined with solubilizing agents, dissolved in organic solvents, or chemically modified to be effectively utilized in practical applications. This physicochemical limitation has historically constrained the development of aqueous undecylenic acid formulations and has been a driver of research into salt forms and novel delivery vehicles such as hexosomes and PMMA composites.
Treating fungal infections is challenging and frequently requires long-term antifungal courses. Given the limited number of existing antifungal drugs, it is crucial to evaluate the possibility of repositioning drugs with antifungal properties and to revisit older antifungals for applications in combined therapy. Regarding antibacterial resistance specifically, serial exposure of MRSA clinical isolates to sub-lethal doses of the GS-1 formulation did not appear to induce resistance; in fact, compared to mupirocin, repeated exposures appeared to sensitize bacteria to GS-1.
Health conditions that Undecylenic acid may help support.
Undecylenic acid (10-undecenoic acid), a naturally occurring fatty acid derived from castor oil, is an FDA-recognized antifungal agent historically used for topical fungal infections. It interferes with Candida fatty acid biosynthesis, preventing the yeast-to-hyphal conversion. Some sources indicate it may be approximately six times more potent than caprylic acid against Candida in certain assays.
Body systems that Undecylenic acid may help support.
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