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Castor oil is a viscous, clear-to-yellowish plant oil obtained by cold pressing the seeds of the Ricinus communis L. plant (family Euphorbiaceae). With a ricinoleic acid content of 85–92%, the richest natural source available, this oil holds a unique position in soapmaking for transparent soap production, foam stability and moisturization. Ricinus communis oil, present in 24 Chailea products, is the most common additive oil used across all product formulations.
This article is not a product promotion. The information in the article contains no treatment claims.
Botanical source
Ricinus communis L. (castor plant / palma christi) is a fast-growing plant native to Africa. Its seeds contain the highly toxic protein ricin. However, ricin does not pass into cold-pressed oil, because the protein is not soluble in oil. India accounts for 80% of global castor oil production.
Chemical profile
Ricinoleic acid: 85–92%
The most distinctive feature of this oil is its ricinoleic acid content of 85–92% (12-hydroxy-9-cis-octadecenoic acid, C18:1-OH). Ricinoleic acid is a rare fatty acid carrying a hydroxyl (-OH) group. This hydroxyl group gives the oil exceptional viscosity, water-binding (humectant) capacity and compatibility with other oils. The raw material is regarded as the only widely known commercial plant oil containing more than 80% ricinoleic acid.
Place in the scientific literature
Emollient and skin barrier
The hydroxyl group of ricinoleic acid may form an occlusive film on the skin surface, which can reduce transepidermal water loss (TEWL). The review by Yeboah et al. (2021), published in Food Science and Technology, comprehensively evaluates the chemical composition and physicochemical properties of Ricinus communis oil. The review by Patel et al. (2016), published in Lipid Insights, assesses the oil's properties, industrial and cosmetic uses, and processing parameters.
Laxative effect (oral — unrelated to cosmetics)
The best-known pharmacological property of castor oil is its strong laxative effect when taken orally. This effect has been shown to occur through ricinoleic acid activating the intestinal EP3 prostanoid receptor (Tunaru et al., 2012). This property is not related to cosmetic use.
Safety profile
The CIR panel has assessed Ricinus Communis Seed Oil as safe for use in cosmetics. It is safe for topical use. Ricin toxin does not pass into cold-pressed oil. Rare cases of contact dermatitis have been reported.
Castor oil in soapmaking
Foam booster and clarity
In soapmaking this vegetable oil plays two critical roles. The first is foam stability: sodium ricinoleate, the soap salt of the oil, stabilizes the foam structure and produces longer-lasting foam. The second is clarity: the oil is a fundamental component in producing clear/transparent soap, as the hydroxyl group of ricinoleic acid contributes transparency to the soap structure. SAP value (NaOH) approximately 0.128. Usage rate: 5–10% (higher rates can make the soap soft and sticky).
Types of castor oil and grades
Cold-pressed castor oil
Cosmetic and soapmaking grade. Clear-yellowish colour, mild odour. USP/BP grade is available. It is the preferred form in soapmaking.
Jamaican black castor oil (JBCO)
A dark brown-black, strongly scented variety obtained by roasting the seeds. It contains terrestrial ash particles. It is popular in hair care, especially for curly and Afro-textured hair. It can be used in soapmaking, but its dark colour and strong scent define the character of the soap.
Industrial castor oil
This raw material is used industrially in the production of bioplastics (polyamide 11, Rilsan), paints and varnishes, lubricants, biodiesel and pharmaceuticals (laxative preparations). The hydroxyl group of ricinoleic acid, with its structure suited to chemical modification, is a valuable starting material for polymer chemistry.
The unique role of castor oil in soapmaking
This oil has a unique role in soapmaking that no other oil can fully replace. Sodium ricinoleate (the soap salt of the oil), unlike other soap salts, can attract both water and oil. Thanks to its amphiphilic structure it increases foam stability. Sodium ricinoleate also gives the soap a slight transparency. In transparent glycerin soaps, castor oil at 5–10% is an indispensable component. It is used in soap at 5–10%; higher rates can make the soap soft and sticky.
Why the 5–10% range? The chemistry of the upper limit
Ricinoleic acid is a rare fatty acid carrying a hydroxyl group on its twelfth carbon. This group allows soap molecules to form stronger hydrogen bonds with water, and the enrichment of the lather and the increase in transparency derive from this. The same property also sets the upper limit: because the hydroxyl group hinders the regular formation of the crystal lattice, as the proportion rises the bar softens, its surface becomes sticky, and its tendency to draw water from humid air increases. The narrow range preferred in formulation lies where these two effects intersect.
Frequently asked questions
What does castor oil do in soap?
It provides foam stability and is a fundamental component of clear soap production. It is used at 5–10%.
Is there a ricin hazard in castor oil?
No. Ricin is part of the protein structure and does not pass into cold-pressed oil. Cosmetic-grade castor oil does not contain ricin.
Castor plant and toxicity note
Ricin: one of the most toxic proteins in the world
Ricinus communis seeds contain ricin, a highly toxic protein; a few milligrams can be fatal. Because of its potential as a biological weapon, ricin is monitored under the "Biological Weapons Convention" and the "Chemical Weapons Convention". However, this toxicity does not concern users of cosmetic-grade oil: ricin is part of the protein structure and is insoluble in oil, it does not pass into the oil during cold pressing, cosmetic-grade castor oil contains no ricin, and topical application is entirely different from exposure through digestion.
History of the castor plant
The castor plant has been known since Ancient Egypt; various traditional uses of the plant are recorded in the Ebers Papyrus (16th century BCE) (Franke et al., 2019). The nickname "Palma Christi" (Christ's palm) reflects the respect held in medieval Europe for the plant's supposed healing properties. India accounts for 80% of global castor oil production, and the state of Gujarat is the main production centre.
Castor oil in hair care
Ricinus communis oil is one of the most widely used vegetable oils in hair care. The humectant property of ricinoleic acid gives it the potential to bind moisture to hair. The claim that it accelerates hair growth is widespread, but there is no strong clinical evidence supporting this claim. The high viscosity of the oil coats the hair strand and may provide protection against mechanical damage.
Castor oil and modern industry
This vegetable oil is becoming increasingly important in modern industry, where petrochemical alternatives are being explored. The hydroxyl group of ricinoleic acid offers a structure highly suited to chemical modification. This enables its use in bioplastic production (Rilsan PA11, the polyamide 11 product of Arkema), in the paint and varnish industry (alkyd resins), in lubricants (high viscosity and thermal stability) and in the pharmaceutical industry (laxative preparations, pharmaceutical coating materials). According to data cited by Patel et al. (2016), world castor oil consumption rose from approximately 400 thousand tonnes in 1985 to approximately 610 thousand tonnes in 2010. Production is largely concentrated in India (Gujarat).
Castor oil and the bioeconomy
The plant from which this oil is obtained is resistant to arid and semi-arid climate conditions and can grow on marginal land, a property valued from the perspective of the bioeconomy and sustainable agriculture. As an oil crop that does not compete with food products, its potential as a raw material for biofuel and bioplastic is being researched.
Chailea products containing this ingredient
Castor oil (Ricinus Communis Seed Oil) is used as a foam stabilizer and clarity provider in 24 Chailea products. View all products →
References
1. Yeboah, A., Ying, S., Lu, J., Xie, Y., Amoanimaa-Dede, H., Boateng, K. G. A., Chen, M., & Yin, X. (2021). Castor oil (Ricinus communis): a review on the chemical composition and physicochemical properties. Food Science and Technology (Campinas), 41(Suppl. 2), 399–413. doi:10.1590/fst.19620
2. Patel, V. R., Dumancas, G. G., Kasi Viswanath, L. C., Maples, R., & Subong, B. J. J. (2016). Castor oil: properties, uses, and optimization of processing parameters in commercial production. Lipid Insights, 9, 1–12. doi:10.4137/LPI.S40233
3. Cosmetic Ingredient Review Expert Panel. (2007). 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. International Journal of Toxicology, 26(Suppl. 3), 31–77. doi:10.1080/10915810701663150
4. Tunaru, S., Althoff, T. F., Nüsing, R. M., Diener, M., & Offermanns, S. (2012). Castor oil induces laxation and uterus contraction via ricinoleic acid activating prostaglandin EP3 receptors. Proceedings of the National Academy of Sciences, 109(23), 9179–9184. doi:10.1073/pnas.1201627109
5. Franke, H., Scholl, R., & Aigner, A. (2019). Ricin and Ricinus communis in pharmacology and toxicology — from ancient use and “Papyrus Ebers” to modern perspectives and “poisonous plant of the year 2018”. Naunyn-Schmiedeberg’s Archives of Pharmacology, 392(10), 1181–1208. doi:10.1007/s00210-019-01691-6