Castor oil (Ricinus communis)

OriginThe plant with two faces

From the same seeds, one obtains a time-tested laxative and one of the strongest known plant poisons.

Castor bean (Ricinus communis) It is a member of the spurge family, a perennial shrub that can grow up to ten meters tall in the tropics, but is cultivated here as an annual ornamental plant – with large, palmately lobed leaves, often tinged with red. The seeds are contained in spiky capsules and are strikingly patterned: glossy, marbled brown, and resembling a engorged tick. Hence the name: ricinus is Latin for tick.

Its use is ancient. Castor beans have been found in Egyptian tombs, the Ebers Papyrus describes the oil, and it was firmly established in Greek and Roman medicine. For centuries, castor oil was the quintessential laxative—effective, fast, and unpleasant enough to be memorable. In Fascist Italy, it became a torture instrument: Squadrists forced large quantities on political opponents, leading to severe dehydration.

The other side of the coin is ricin. It's a protein belonging to the group of ribosome-inactivating toxins and is one of the most potent known plant poisons; a few thoroughly chewed seeds can be fatal to a child. Crucially, ricin is a protein and not fat-soluble. When pressed, it remains completely in the press cake, which is used as fertilizer or heat-treated. The oil itself contains no ricin—a fact that is often misunderstood and explains why a product from a highly poisonous plant can be sold without hesitation in pharmacies.

To useA reliable laxative - and many unproven uses

The European Medicines Agency lists castor oil as traditional use For the short-term treatment of occasional constipation. Commission E also gave it a positive assessment. The mechanism of action is well understood: In the small intestine, lipases break down the oil, and the released ricinoleic acid binds to a specific prostaglandin receptor in the intestinal wall. This leads to increased contraction of the smooth muscle and reduced water reabsorption – the intestinal contents remain liquid and are transported more quickly.

The effect is reliable and sets in after two to six hours. However, this is precisely what makes castor oil a remedy rarely recommended today: its effect is drastic, can cause cramping abdominal pain, and is difficult to control. For occasional constipation, bulking agents such as psyllium husk or mild osmotic diuretics are a better and more tolerable choice. Castor oil remains useful in situations where rapid and complete bowel movement is desired.

One traditional use deserves clear clarification: inducing labor. Castor oil has been used for centuries for this purpose, and studies have shown it can trigger contractions—the mechanism via prostaglandin receptors is plausible. However, the data on its safety and efficacy are insufficient, and its use can cause severe diarrhea, dehydration, and vomiting. A Cochrane review found insufficient evidence. Labor induction belongs in the hands of obstetricians, not in the kitchen.

And then there are the cosmetic applications that have given castor oil its current popularity: eyelash and eyebrow growth, hair growth, and skincare. The facts are simple: there are no clinical studies that prove castor oil promotes hair or eyelash growth. What the oil does is coat the hair – making it look fuller and shinier, which creates the impression of more hair. As a conditioner, it's fine. As a growth stimulant, it's unsubstantiated.

IngredientsRicinoleic acid - a special case among fatty acids

Castor oil is unique among vegetable oils: around ninety percent of its fatty acids are ricinoleic acid, an unsaturated fatty acid with an additional hydroxyl group. This hydroxyl group makes the oil significantly more polar than other vegetable oils and explains its unusual physical properties: very high viscosity, good solubility in alcohol, and the ability to remain liquid even at low temperatures.

This makes castor oil an important industrial raw material, far beyond medicine. It is a starting material for polyamide 11, for lubricants that withstand extreme temperatures, for hydraulic fluids, paints, and varnishes. In early aviation, castor oil was the standard lubricant for rotary engines—with the well-known side effect that pilots inhaled the oil mist and experienced its laxative effect.

Ricin is chemically a completely different story. It's a lectin consisting of two protein chains: one binds to the cell surface, the other penetrates and blocks the ribosomes, the cell's protein factories. The affected cell dies. Because ricin is a large protein, it's neither fat-soluble nor heat-stable—it remains after pressing and is destroyed by heating. For the same reason, whole seeds swallowed without chewing are less dangerous than chewed ones: the hard shell provides protection.

This leads to a clear warning for gardeners. Castor beans are a popular ornamental plant with spectacular leaves, and their patterned seeds look interesting – attractive enough for children to put in their mouths. Therefore, they have no place in homes and gardens with small children. If ingestion is suspected, contact poison control immediately.

Enhanced combinationsWhat castor oil is good for

An effective but drastic laxative and a useful care oil - more, but also nothing less.

What contradicts itselfIt's best to avoid these combinations.

ApplicationApplications from the pharmacy to the soap pot

• laxative10 to 30 ml once, chilled and stirred into juice - takes effect in two to six hours.
• Hair treatmentMix with coconut or olive oil 1:1, leave on for one hour, then rinse thoroughly.
• eyebrowsApply thinly in the evening with a clean brush - as a treatment, not as a growth promoter.
• HeelsApplied to cracked heels, socks over them, overnight.
• cuticleMassage a drop into the nail fold.
• SoapFive to ten percent in the soap recipe for creamy lather.
• Lip careIn balms as a shine and adhesion component.
• Cold-pressedFor cosmetic and internal use, always use cold-pressed pharmaceutical-grade products.
• storageDark and sealed; it is relatively oxidation-stable and lasts a long time.
• Not the seedsThe plant is ornamental, the seeds are poisonous - the two must be kept separate.

As a home remedyHair and eyebrow care

Ayurveda & TCMWhat the old systems say

Warning noticesWhen you should be careful

This page provides information and does not replace medical advice. If symptoms persist, please consult a doctor.

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