Castor oil is a pale yellow, viscous vegetable oil obtained by pressing the seeds (beans) of the castor oil plant, Ricinus communis, the sole species in the genus Ricinus of the Euphorbiaceae (spurge) family. Castor oil is unique among vegetable oils due to its exceptionally high content of ricinoleic acid, a hydroxylated fatty acid that gives it distinctive physical and chemical properties.
The castor plant is native to the tropical regions of East Africa, most likely Ethiopia, and has been cultivated for at least 6,000 years. The scientific name Ricinus means "tick" in Latin, referring to the resemblance of the seed to certain tick species.
The castor plant is a fast-growing perennial shrub or small tree that can reach heights of 5-12 metres in tropical climates. It thrives in warm, semi-arid conditions and is cultivated commercially in India, China, Brazil, Mozambique, and Ethiopia. India dominates global castor oil production, accounting for approximately 85-90% of world supply. Global annual production of castor oil is approximately 700,000-800,000 metric tonnes.
The production of castor oil begins with the harvesting of mature castor seed capsules, which contain three seeds each. After drying and dehulling, the seeds (containing approximately 45-55% oil) are mechanically pressed using expeller presses. The crude castor oil is then filtered, degummed, and refined to produce commercial grades. It is important to note that castor seeds contain ricin, a highly toxic protein, but this toxin is not present in the expressed oil — it remains in the seed cake, which requires detoxification before use as animal feed or fertiliser.
Chemically, castor oil is unique due to its extraordinarily high ricinoleic acid content — approximately 85-92% of total fatty acids. Ricinoleic acid (12-hydroxy-9-cis-octadecenoic acid) is an 18-carbon fatty acid with one double bond and a hydroxyl group at the C-12 position. This hydroxyl group is responsible for castor oil's exceptional viscosity, polarity, solubility properties, and chemical reactivity. Castor oil has a density of approximately 0.96 g/cm3 — the highest of any common vegetable oil — and a viscosity approximately 100 times greater than most vegetable oils.
Historically, castor oil has been used for thousands of years. Ancient Egyptians used castor oil as lamp fuel, in cosmetics, and medicinally as a purgative — castor oil seeds have been found in Egyptian tombs dating to 4000 BCE. In Ayurvedic medicine, castor oil (eranda taila) has been used for centuries for its anti-inflammatory, analgesic, and laxative properties.
In modern industrial applications, castor oil is one of the most versatile and valuable vegetable oils. Its unique chemistry allows it to be converted into hundreds of derivatives through chemical reactions including hydrogenation, dehydration, oxidation, esterification, saponification, sulfonation, and polymerisation.
Major industrial products derived from castor oil include: sebacic acid (used in nylon 610, plasticisers, and lubricants), undecylenic acid (an antifungal agent), 12-hydroxystearic acid (a lubricant grease thickener), ricinoleic acid esters (bio-based plasticisers), and polyurethane polyols (for coatings, adhesives, and foams).
In the pharmaceutical and cosmetic industries, castor oil is used in topical medications, laxatives, eye drops, lipstick, hair care products (particularly for promoting hair growth), skin moisturisers, and as a carrier oil for drug delivery systems. In the food industry, castor oil and its derivatives are used as food-grade lubricants, release agents, flavouring adjuvants, and in food-contact packaging.
Interesting facts about castor oil include: it is the only commercial source of a hydroxylated fatty acid; castor oil was used as an aircraft engine lubricant in World War I (it does not mix with petroleum fuels, preventing dilution); the castor plant is one of the fastest-growing plants in the world, capable of growing 3 metres in a single season; and castor oil-based polyurethanes are among the most important bio-based polymers in commercial production today.