--- topic: "Castor Oil" title: "Ricinoleic Acid: What Castor Oil's Main Fatty Acid Does" order: 1 description: "What ricinoleic acid, the main fatty acid in castor oil, does in the body: a stimulant laxative acting through EP3 receptors, a capsaicin-like anti-inflammatory in animal studies, and a skin-conditioning cosmetic ingredient." question: "Does castor oil really treat inflammation, skin, hair and constipation?" answer: "Castor oil may help inflammation, skin and hair, but only its laxative effect is well established; other uses rest on mechanism and tradition." actions: - "For occasional constipation, the typical adult dose is 15–60 mL, working within 2–6 hours [3]." - "For skin or castor oil packs, choose organic, cold-pressed, hexane-free oil in glass bottles [2]." - "Treat hair and eyebrow use as traditional, not clinically proven; it coats hair shafts, but trials are lacking [4]." cautions: - "Castor oil also triggers uterine contraction via the same receptor, so do not use it internally in pregnancy without medical advice [3]." - "Safety evidence covers topical and short-term internal use only [2]." confidence: 2 confidenceNote: "Laxative use: mechanism study and FDA classification; anti-inflammatory support is receptor-level, hair claims rest on a survey; no clinical trials cited." evidenceSummary: rctCount: 0 metaAnalysisCount: 0 replicated: false newestStudyYear: 2017 references: - id: "1" pmid: "11200362" title: "Effect of ricinoleic acid in acute and subchronic experimental models of inflammation" authors: "Vieira C, Evangelista S, Cirillo R, Lippi A, Maggi CA, Manzini S" year: 2000 journal: "Mediators of Inflammation" - id: "2" pmid: "18080873" url: "https://pubmed.ncbi.nlm.nih.gov/18080873/" title: "Final report on the safety assessment of Ricinus Communis (Castor) Seed Oil, Hydrogenated Castor Oil, Glyceryl Ricinoleate, Glyceryl Ricinoleate SE, Ricinoleic Acid, Potassium Ricinoleate, Sodium Ricinoleate, Zinc Ricinoleate, Cetyl Ricinoleate, Ethyl Ricinoleate, Glycol Ricinoleate, Isopropyl Ricinoleate, Methyl Ricinoleate, and Octyldodecyl Ricinoleate" authors: "Cosmetic Ingredient Review Expert Panel" year: 2007 journal: "International Journal of Toxicology" - id: "3" pmid: "22615395" url: "https://pubmed.ncbi.nlm.nih.gov/22615395/" title: "Castor oil induces laxation and uterus contraction via ricinoleic acid activating prostaglandin EP3 receptors" authors: "Tunaru S, Althoff TF, Nüsing RM, Diener M, Offermanns S" year: 2012 journal: "Proceedings of the National Academy of Sciences" - id: "4" pmid: "28679382" url: "https://pubmed.ncbi.nlm.nih.gov/28679382/" title: "Ethnopharmacological survey of home remedies used for treatment of hair and scalp and their methods of preparation in the West Bank-Palestine" authors: "Zaid AN, Jaradat NA, Eid AM, Al Zabadi H, Alkaiyat A, Darwish SA" year: 2017 journal: "BMC Complementary and Alternative Medicine" --- Castor oil is extracted from the seeds of the *Ricinus communis* plant and has been used medicinally for thousands of years. What makes it unusual among plant oils is that roughly 90% of its fatty acid content is ricinoleic acid — a rare hydroxylated fatty acid found in almost no other natural source. Researchers credit ricinoleic acid with most of castor oil's pharmacological effects, and they have worked out how it acts as a laxative [3] and how it behaves in animal models of inflammation [1]. ## How Ricinoleic Acid Works Castor oil is broken down by pancreatic enzymes in the small intestine, releasing glycerol and ricinoleic acid [2]. Ricinoleic acid then specifically activates the EP3 prostaglandin receptor. In mice lacking EP3 receptors, castor oil's laxative effect and its ability to contract the uterus are absent, and the effect depends on EP3 receptors in smooth-muscle cells [3]. Although ricinoleic acid is chemically similar to prostaglandin E1, it did not show the same physiological properties in the safety assessment [2]. Ricinoleic acid's anti-inflammatory effect, seen in animal models, works differently. When it is applied to the skin repeatedly for several days, it reduced experimentally induced swelling in mice and guinea pigs, and lowered tissue levels of substance P, a pain and inflammation neuropeptide. Its effects resemble those of capsaicin, the hot compound in chili peppers, but without the burning sensation, so the authors describe it as a possible capsaicin-like, non-pungent anti-inflammatory agent [1]. The first, single application actually increased swelling, so the effect appears only with repeated use. These findings are from animals; they do not show that castor oil reduces inflammation in people. ### Castor Oil Packs One of the most traditional applications is the castor oil pack — a cloth soaked in castor oil, placed over the abdomen or liver area, often with gentle heat. Practitioners report benefits, but there is almost no clinical research on packs. See our [castor oil packs page](/castor-oil/castor-oil-packs) for what the single study found, and for the cautions about heat and pregnancy. ### Constipation and Labor Castor oil is classified by the FDA as generally recognized as safe and effective for use as a stimulant laxative [2]. The mechanism was clarified in 2012, when researchers showed that ricinoleic acid acts on EP3 receptors in intestinal smooth-muscle cells [3]. The same pathway contracts the uterus, which is why swallowing castor oil has been used to induce labor and why pregnant women should not take it unsupervised [3]. ### Skin and Hair Castor oil and its derivatives function primarily as skin-conditioning agents, emulsion stabilizers, and surfactants in cosmetics, and castor oil and ricinoleic acid can also help other chemicals penetrate the skin [2]. For hair, castor oil is widely used in folk practice, but the evidence for hair growth is not there: a survey of home remedies used for hair and scalp problems in the West Bank documents what people use, not whether it works [4]. ## Safety and Sourcing The cosmetic-ingredient safety assessment [2] reports that castor oil is made by cold pressing the seeds and then clarifying the oil with heat, and that castor oil does not contain ricin, because ricin does not partition into the oil. It describes these ingredients as not acute toxicants; a National Toxicology Program subchronic oral study giving castor oil at up to 10% of the diet of rats was not toxic. Undiluted castor oil was severely irritating to rabbit skin in one study but only slightly or mildly irritating in others, and ricinoleic acid caused well-defined redness at intact and abraded skin sites in one rabbit study, so patch-testing a new product is sensible. ## What the Research Shows The laxative mechanism of ricinoleic acid is well established at the receptor level in mice [3]. Its anti-inflammatory effect has been shown in animal models and resembles capsaicin's [1]. The safety assessment found a low toxicity profile in animal and cosmetic-use data [2]. The gaps are in human studies: there are few clinical trials for specific applications like castor oil packs and hair growth, where traditional use far outpaces formal study [4].