|Jmol-3D images||Image 1|
|Molar mass||184.28 g mol−1|
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Undecylenic acid is an organic unsaturated fatty acid derived from castor oil. It is the common name of 10-undecenoic acid, (CH2CH(CH2)8COOH). It is used in the manufacture of pharmaceuticals, cosmetics and perfumery, including antidandruff shampoos, antimicrobial powders and as a musk in perfumes and aromas. Undecylenic acid is produced by cracking of castor oil under pressure.
Medicinal uses 
Undecylenic acid is also FDA-approved for over-the-counter use on skin disorders or skin problems. Castor oil penetrates deep into the skin due to its molecular mass, which is low enough to penetrate into the stratum corneum. Castor isostearate succinate is a polymeric mixture of esters with isostearic acid and succinic acid used for skin conditioning, such as in shampoo, lipstick and lip balm.
Undecylenic acid is the active ingredient in medications for skin infections, and relieves itching, burning, and irritation. For example, it is used against fungal skin infections, such as athlete's foot, ringworm, jock itch or Candida albicans. When used for jock itch, it can result in extreme burning, as the skin is rather sensitive. It is also used in the treatment of psoriasis. Undecylenic acid has antiviral properties that are effective on skin infections such as herpes simplex.
At least one of the mechanisms underlying its antifungal effects observed is its inhibition of morphogenesis of Candida albicans. In a study on denture liners, undecylenic acid in the liners was found to inhibit conversion of yeast to the hyphal form. Hyphae were associated with active infection. The mechanisms of action appear to be interference with fatty acid biosynthesis, which can inhibit germ tube (hyphae) formation. Medium-chain fatty acids have also been shown to disrupt the pH of the cell cytoplasm by being proton carriers, which interferes with viral replication mechanisms in infected cells. The mechanism of action and effectiveness in fatty acid based antifungals is dependent on the number of carbon atoms in the chain, being more effective as the number of atoms in the chain increases (Undecylenic acid has 11).
Other uses 
Undecylenic acid can be used in silicon-based biosensors. Monolayers can be made on bare silicon transducer surfaces with the help of covalent bonds between silicon atom and the double bonds of undecylenic acid. The carboxylic acid groups remain available for the conjugation of biomolecules such as DNA or proteins.
- "United States International Trade Commission Memorandum" (PDF). USITC. Archived from the original on 2006-09-24. Retrieved 2007-01-02. - see page 2 of link
- Katz, G; Watt, JA (1992). "Undecylenic Acid in Psoriasis". CMAJ 37 (3): 173–8. PMC 1591667. PMID 18140580. Retrieved 2007-01-05. - see page 2/362 of link
- "Ingredient List P-Z" (PDF). FDA (see page 65 of this link). Archived from the original on 2006-10-16. Retrieved 2006-12-28.
- Skin-Conditioning Agents by the Environmental Working Group.
- "Ingredient List P-Z" (PDF). FDA. Archived from the original on 2006-10-16. Retrieved 2007-01-02. - see page 65 of this link
- "Undecylenic Acid in Psoriasis" (PDF). CMAJ. Retrieved 2007-01-05. - see page 4/364 of link
- Bourne, N; Ireland, J; Stanberry, LR; Bernstein, DI (1999). "Effect of undecylenic acid as a topical microbicide against genital herpes infection in mice and guinea pigs". Antiviral Res 40 (3): 139–44. doi:10.1016/S0166-3542(98)00055-2. PMID 10027648.
- "Undecyclic Acid". Retrieved 2008-07-09.
- A. Moraillon, A. C. Gouget-Laemmel, F. Ozanam, and J.-N. Chazalviel (2008). "Amidation of Monolayers on Silicon in Physiological Buffers: A Quantitative IR Study". J. Phys. Chem. C 112 (18): 7158–7167. doi:10.1021/jp7119922.