What Is Castor Oil Made From? Source, Extraction & Types

Castor oil comes from the seeds of the castor plant, Ricinus communis, a fast-growing tropical species that thrives in warm climates around the world. The seeds, often called “castor beans” despite not being true beans, contain roughly 45 to 55 percent oil by weight, and the oil’s unusual chemistry sets it apart from every other commercially available vegetable oil. What makes it unique is a single fatty acid called ricinoleic acid, which accounts for about 75 to 90 percent of the total oil composition and gives castor oil properties no other plant oil can match.

The Castor Plant and Its Seeds

Ricinus communis is a member of the spurge family and likely originated in East Africa, though it now grows on every inhabited continent. The plant ranges from a small annual shrub in temperate zones to a tree-like perennial in the tropics, sometimes reaching several meters in height. Its large, star-shaped leaves and spiny seed pods are distinctive, and the seeds themselves are strikingly patterned with brown and gray mottling. Traditional medicine systems including Ayurveda, Unani, and Siddha have used various parts of the plant for centuries to manage inflammation, skin disorders, constipation, and joint pain.¹

Inside each seed, the endosperm cells have a porous structure packed with tiny lipid bodies, and microscopy work has shown these oil-storing structures sit at a density of roughly 9 to 10 lipid bodies per square micrometer, closely associated with proteins and minerals like potassium, phosphorus, and magnesium.² That dense, oil-rich endosperm is the source of all commercially produced castor oil.

Castor plants are appealing for cultivation because they grow readily even on poor or arid land and do not compete with food crops for prime agricultural space. This has made castor a candidate for sustainable biodiesel production in addition to its traditional industrial roles.³ India is the world’s dominant producer, followed by Mozambique, China, and Brazil, and global demand has been climbing steadily as industries seek renewable alternatives to petroleum-derived chemicals.

What Makes Castor Oil Chemically Unusual

Nearly all of castor oil’s interesting properties trace back to one molecule: ricinoleic acid. This is a monounsaturated fatty acid with an 18-carbon chain, one double bond, and a hydroxyl group hanging off the 12th carbon. That hydroxyl group is the key. No other major vegetable oil has it in anything close to the same concentration, and it is responsible for castor oil’s unusually high viscosity, its miscibility with alcohol, its ability to form films and coatings, and its biological activity in the body.⁴

The remaining fraction of the oil is a mix of oleic, linoleic, stearic, palmitic, and linolenic acids, but these together make up only about 10 to 25 percent. Because the saturated fat content is very low (under 4 percent in some analyses), castor oil also behaves well at low temperatures, resisting the thickening and solidification that plague many other bio-based lubricants.⁵ That combination of high viscosity at room temperature and good fluidity when cold is hard to engineer synthetically, which is one reason castor oil has remained commercially relevant for well over a century.

How Castor Oil Is Extracted

Getting the oil out of the seeds involves either mechanical pressing, solvent extraction, or some combination of the two. The method chosen has a big impact on the quality, purity, and intended use of the finished oil.

• Cold pressing: The seeds are crushed at relatively low temperatures, usually below about 50°C, without chemical solvents. This yields the highest-quality oil with minimal degradation of the fatty acids. Cold-pressed castor oil is pale yellow, nearly odorless, and is the grade typically sold for cosmetic and pharmaceutical use. The trade-off is lower yield: cold pressing leaves a significant amount of oil behind in the seed cake.
• Hot pressing (expeller): Seeds are heated before or during mechanical pressing, which increases oil yield. The higher temperature also has a practical safety benefit discussed below. Hot-pressed oil tends to be darker and may have a slightly stronger odor.
• Solvent extraction: After pressing, the remaining seed cake still holds oil. Industrial operations often use a solvent, typically hexane, to pull out this residual oil. The solvent is then evaporated off. Solvent-extracted oil is lower grade and usually destined for industrial products rather than personal care.

Commercial production frequently combines pressing with solvent extraction to maximize total oil recovery. The oil then goes through refining steps like degumming, neutralization, bleaching, and deodorizing, depending on the end use.⁶

What About Ricin in the Seeds?

If you have heard of ricin, the notoriously toxic protein, you might wonder why anyone would put castor oil on their skin or swallow it as a laxative. Ricin is indeed found in castor seeds and in the seed meal left after pressing. But the oil extraction process effectively separates the toxin from the oil. Ricin is a water-soluble protein, so it stays behind in the press cake rather than dissolving into the fat-based oil. Research has confirmed that hot pressing denatures the ricin in the seed meal so thoroughly that antibody tests can no longer detect it in the pressed material.⁷ The finished, refined oil that reaches consumers contains no meaningful amount of ricin, which is why regulatory bodies have long considered it safe for both topical and oral use.

The U.S. Food and Drug Administration classifies castor oil as “generally recognized as safe and effective” (GRASE) for use as a stimulant laxative. For food-additive purposes, the joint FAO/WHO committee set an acceptable daily intake of up to 0.7 mg per kilogram of body weight. The Cosmetic Ingredient Review panel has also concluded that castor oil and its derivatives are safe at the concentrations used in cosmetics.⁸

Types of Castor Oil

Walk into a health food store or scroll through an online marketplace and you will encounter several varieties of castor oil, sometimes with confusing labeling. The differences are real and worth understanding.

Cold-Pressed (Virgin) Castor Oil

This is the standard form most people encounter. It is extracted mechanically without heat or solvents, retains its full complement of ricinoleic acid, and has a pale straw color. It is the go-to grade for hair and skin care, as well as for use as a laxative. Labels may say “virgin,” “cold-pressed,” or “expeller-pressed,” though the distinctions among these terms are less regulated than in the olive oil world.

Jamaican Black Castor Oil

This variety has a devoted following, particularly in hair-care communities. The difference is in processing: the castor beans are roasted before pressing, which darkens the oil and gives it a characteristic smoky, ashy scent. The roasting also raises the pH slightly because of the ash content. Proponents claim it penetrates hair and skin more effectively, though controlled studies comparing it head-to-head with regular cold-pressed castor oil are scarce. The color can range from dark brown to nearly black.

Hydrogenated Castor Oil (Castor Wax)

When hydrogen gas is added to castor oil under pressure with a catalyst, the double bonds in the fatty acid chains become saturated. The result is a hard, brittle, waxy solid with a high melting point, commonly called castor wax. Researchers have explored it as a substitute for beeswax and carnauba wax in packaging coatings, producing materials with melting points around 98 to 130°C and hardness several times greater than beeswax.⁹¹⁰ In personal care products, hydrogenated castor oil shows up as a thickener, emollient, and emulsifier in lipsticks, deodorants, and creams. It is worth noting that the hydrogenation process removes the ricinoleic acid structure, which has implications for allergic reactions discussed later.

Dehydrated Castor Oil (DCO)

Removing water from the ricinoleic acid molecule creates a second double bond in the fatty acid chain, producing what is essentially a drying oil. Dehydrated castor oil behaves like tung oil: it dries to a hard, water-resistant film when exposed to air. That makes it valuable for paints, varnishes, and protective coatings, where it delivers good flexibility, fast drying, and strong color retention.¹¹ Various catalytic methods can fine-tune the degree of conjugation in the double bonds, which affects how quickly and thoroughly the oil dries.¹²

Sulfated Castor Oil (Turkey Red Oil)

This is the first synthetic surfactant ever made, dating back to the textile industry of the 19th century. Treating castor oil with sulfuric acid attaches sulfate groups to the fatty acid chains, making the oil water-dispersible. The result, known as Turkey Red Oil, is still used as a wetting agent in textile dyeing and in some bath oil formulations. Unlike other castor oil types, it mixes freely with water rather than floating on top of it.

How Castor Oil Works as a Laxative

Castor oil’s reputation as a powerful laxative goes back millennia, but the mechanism was not pinned down until surprisingly recently. When you swallow castor oil, enzymes in the small intestine break down the triglycerides and release free ricinoleic acid. That ricinoleic acid then activates a specific receptor on the cells lining the intestine, the EP3 prostanoid receptor, which triggers smooth muscle contraction and fluid secretion. Research in mice confirmed that animals lacking EP3 receptors showed no laxative response to ricinoleic acid at all.¹³ The same receptor mechanism explains why castor oil has historically been associated with stimulating uterine contractions, a use that carries real risks and should not be attempted without medical supervision.

Skin and Hair Applications

Castor oil is a staple in cosmetic formulations, and its benefits on skin are largely physical rather than pharmacological. Applied topically, it acts as an occlusive barrier, meaning it sits on the skin surface and slows the rate at which water evaporates. Laboratory studies using skin membranes have demonstrated that castor oil markedly reduces transepidermal water loss, functioning similarly to mineral oil and sesame oil as a moisture-sealing agent.¹⁴ This is the basis for its use in lip balms, thick creams, and hair treatments: it helps prevent moisture from escaping rather than adding moisture directly.

For hair, castor oil’s high viscosity means it coats the hair shaft effectively, giving the appearance of thicker, shinier strands. Claims that it stimulates new hair growth are widespread but not well supported by clinical trials. Most of the perceived benefit likely comes from the coating effect, which reduces breakage and makes existing hair look healthier.

Eye Care and Dry Eye

One of the more surprising uses of castor oil is in eye drops for dry eye and meibomian gland dysfunction, a condition where the tiny oil-producing glands in the eyelids become blocked and stop contributing their lipid layer to the tear film. Without that lipid layer, tears evaporate too quickly. Castor oil eye drops can supplement the missing lipids, improving tear film stability and reducing evaporation. A pilot study found that castor oil emulsion drops achieved a residence time of at least four hours on the eye surface and produced a more stable tear film along with significantly reduced symptoms in people with dry eyes.¹⁵

In a study focused specifically on meibomian gland dysfunction, low-concentration castor oil eye drops improved symptom scores, tear stability, and gland obstruction compared with placebo, with no complications attributed to the drops.¹⁶ Researchers have also reviewed castor oil’s broader therapeutic potential for managing blepharitis and related eyelid conditions, noting its ability to increase the thickness of the tear film lipid layer.¹⁷ If you have chronically dry or irritated eyes, you may already be using an over-the-counter drop that contains castor oil without realizing it.

Industrial Uses Beyond the Medicine Cabinet

The majority of globally produced castor oil never ends up in a bottle on a bathroom shelf. It goes into factories. Because castor oil is a natural polyol, meaning it has reactive hydroxyl groups built right into its fatty acid chains, it serves as a starting material for a remarkable range of polymers. Researchers have used it to produce polyurethanes, polyesters, polyamides, and epoxy resins, all derived from a renewable, non-edible plant source rather than petroleum.¹⁸¹⁹

Biodegradable polyurethanes made from castor oil are an active area of research, with potential applications in biomedical materials and packaging that break down after use.²⁰ The fact that castor oil is non-edible gives it an advantage over soybean or palm oil as a polymer feedstock: scaling up production does not pull land or resources away from food. Castor oil also shows up in lubricants, brake fluids, hydraulic fluids, nylon production (nylon-11 is derived from castor oil), and as a plasticizer in various products.

Allergic Reactions and Who Should Be Cautious

Castor oil is well tolerated by most people, but allergic contact dermatitis does occur in a small number of individuals. The pattern that has emerged across case reports is telling: the allergenic culprit appears to be ricinoleic acid itself. In one case, a patient who reacted to non-hydrogenated castor oil in a wound dressing showed no reaction to hydrogenated castor oil, and further analysis confirmed that only the non-hydrogenated form contained ricinoleic acid. More broadly, adverse reactions have been most commonly associated with non-hydrogenated castor oil, while hydrogenated and chemically modified derivatives carry a lower risk of triggering allergic contact dermatitis.²¹

Reported reactions have included lip dermatitis from lipsticks, underarm irritation from deodorants, and in one notable case, facial swelling and hive-like lesions after using an ear wax removal product containing castor oil.²² These cases are rare, but if you develop unexplained skin irritation around the lips, underarms, or anywhere else you apply a product, it is worth checking the ingredient list for castor oil or ricinus communis seed oil. Patch testing with the oil itself can confirm or rule out the allergy.

Castor Oil Esters and Specialty Derivatives

Beyond the major types already described, chemists have created a library of castor oil esters by reacting the oil with various fatty acids. These esters have markedly different physical properties from the parent oil. For instance, reacting castor oil or hydrogenated castor oil with fatty acids ranging from six to eighteen carbons long produces esters with very low melting points, some remaining liquid even below freezing. The lowest reported slip melting point was negative 6°C for a short-chain castor oil ester, while the highest was 21°C for a long-chain hydrogenated castor oil ester.²³ These specialty esters find use as emollients in personal care products, as lubricant additives, and in other applications where a specific viscosity or melting behavior is needed. The ability to dial in precise physical properties by choosing different ester combinations is part of what makes castor oil so versatile as an industrial feedstock, and why researchers keep finding new uses for a plant oil that humans first pressed thousands of years ago.