Plants & Health · October 28, 2026

Castor oil: benefits, dosage and precautions

Huile de ricin : bienfaits, dosage et précautions

Castor oil, known in Morocco as zit el kharwa3 (زيت الخروع), is one of the most widely used beauty remedies in traditional Moroccan herbal medicine. Extracted from the seeds of the castor plant (Ricinus communis), this thick, golden oil has been passed down from generation to generation to strengthen hair, nourish eyelashes and soften the skin. Behind this reputation lies a chemical composition that is unique in the plant world, but also a set of precautions that are worth knowing before you use it.

Cold-pressed castor oil, rich in ricinoleic acid — Castor oil owes its unique viscosity to ricinoleic acid.

What is castor oil?

The castor plant is a shrub of the Euphorbiaceae family, native to tropical Africa and widely naturalised around the Mediterranean, including in Morocco, where it grows along roadsides and on waste ground. Its large palmate leaves, divided into seven to eleven lobes, are distinctive, as are its spiny capsules, which hold mottled seeds that look like ticks — hence the Latin name ricinus.

It is these seeds that are pressed to obtain the oil. One point deserves to be cleared up straight away: castor seeds contain ricin, a highly toxic protein. Because this toxin is water-soluble rather than fat-soluble, it does not pass into the oil during pressing. A properly cold-pressed and filtered oil is therefore free of ricin. This is precisely why you should choose a virgin, cold-pressed oil of cosmetic or pharmaceutical grade, and never eat the seeds themselves.

Composition and active compounds of castor oil

The signature of castor oil comes down to a single compound: ricinoleic acid, which makes up more than 85% of its fatty acid profile. It is a hydroxylated monounsaturated fatty acid, meaning it carries a hydroxyl group (-OH) on its carbon chain. No other common vegetable oil contains it in any significant amount, which makes this oil an ingredient in a class of its own.

This hydroxyl group explains most of its properties:

Ricinoleic acid (over 85%): responsible for the oil’s exceptional viscosity, its occlusive power and its documented anti-inflammatory and antimicrobial properties.
Oleic acid: a softening omega-9 fatty acid, also the main fatty acid in olive oil.
Linoleic acid: an essential omega-6 that helps maintain the integrity of the skin barrier.
Stearic and palmitic acids: saturated fatty acids present in small amounts.
Vitamin E and tocopherols: natural antioxidants that improve the oil’s oxidative stability.

This very high viscosity, several times greater than that of other vegetable oils, is not a flaw: it is what allows the oil to form a long-lasting protective film on the surface of the hair fibre and the skin.

The benefits of castor oil

Nourishing dry hair and reducing breakage

This is its most common use in Morocco. Thanks to its occlusive nature, castor oil seals the hair cuticles and limits water loss from the fibre. On lengths that are dry, porous or damaged by colouring and heat, it restores suppleness and shine, and mechanically reduces breakage and split ends. It is especially popular for coily, curly and wavy hair, which is naturally drier.

Soothing the scalp

The anti-inflammatory and antimicrobial properties of ricinoleic acid help soothe a scalp that is irritated, flaky or prone to itching. A healthy scalp is better ground for hair growth. We should be honest, however: to date, no clinical study has shown that castor oil directly speeds up hair growth. The visible results come mainly from better length retention — in other words, less breakage.

Strengthening eyelashes and eyebrows

Applied in the evening in a very small amount, the oil coats each hair and makes it look fuller and more supple. Here again, the documented effect is one of coating and protection, not proven follicle stimulation. Caution is needed around the eye: a single drop is enough, placed along the lash line without touching the mucous membrane.

Moisturising and soothing the skin

On the driest areas — elbows, knees, heels, chapped lips — castor oil forms a protective film that slows water evaporation and leaves the skin softer. Its anti-inflammatory action also makes it a popular supporting treatment for minor irritations. As its texture is very thick, it is often diluted in a lighter oil such as argan oil or sweet almond oil.

Strengthening nails and cuticles

Massaged daily into the nail and the surrounding skin, it softens the cuticles and reduces peeling in fragile nails. Its antifungal properties also make it a common complementary treatment for damaged nails, although it does not replace a prescribed antifungal treatment.

A powerful laxative effect when taken orally

This is the oil’s historical use in pharmacy. In the intestine, the ricinoleic acid that is released activates specific receptors on the smooth muscle of the gut, triggering contractions and faster transit. The effect is quick and powerful — far stronger than that of other oils — which also makes it the most delicate use and the one that calls for the most supervision. It is by no means a remedy to take every day.

How to use it and dosage

External use (hair, skin, eyelashes, nails)

Hair oil treatment: mix one to two tablespoons of castor oil in equal parts with a lighter oil (argan, olive, sweet almond). Apply to dry hair from roots to ends, massage the scalp, leave on for 30 minutes to overnight, then wash with a gentle shampoo — often twice, as the texture is so stubborn.
Frequency: once or twice a week is enough. More is not better: applying it too often weighs the hair down and can clog the follicles.
Eyelashes and eyebrows: one drop applied in the evening with a clean cotton bud or a dedicated mascara wand, avoiding contact with the eye.
Nails: a few drops massaged into the nail plate and cuticles every evening.
Skin: neat on very dry, localised areas, or diluted at 10–20% in a vegetable oil for wider application.

Internal use

Taken orally, the dose usually cited for adults is one to two tablespoons, as a single, occasional dose, never repeated several days in a row without medical advice. The effect generally occurs within two to six hours. This use should remain occasional and ideally be approved by a doctor or pharmacist: repeated self-medication carries a risk of dehydration and electrolyte imbalances. Castor oil is never a long-term treatment for constipation; fibres such as psyllium are far better suited over time.

Precautions and contraindications

Pregnancy: oral use is strictly not recommended. Ricinoleic acid can trigger uterine contractions, with a risk of premature labour and complications for mother and baby.
Breastfeeding and young children: avoid internal use, as there is not enough safety data.
Digestive disorders: oral use is contraindicated in cases of intestinal obstruction, abdominal pain of unknown origin, chronic inflammatory bowel disease or suspected appendicitis.
Gallstones and heart conditions: seek medical advice before any oral use.
Prolonged oral use: it can reduce the absorption of fat-soluble vitamins (A, D, E, K) and lead to the colon becoming dependent on laxatives.
Drug interactions: faster transit can reduce the absorption of certain medicines. Space out doses and ask a pharmacist for advice.
Allergies: although rare, skin reactions are possible. Do a patch test in the crook of the elbow 24 hours before the first application.
Seeds: never swallow castor seeds, which contain ricin, a toxin that is deadly even in small doses.

Castor oil FAQ

Does castor oil really make hair grow?

No clinical study has demonstrated this so far. What the oil does in a documented way is nourish the hair fibre, soothe the scalp and reduce breakage. As a result, lengths are better preserved, which gives the impression of faster growth. It is a real effect, but its mechanism is not the one people think.

How do you get castor oil out of your hair?

Its viscosity makes it hard to rinse out. Two tips: always dilute it in a lighter oil before applying, and apply shampoo to dry hair before wetting it, working it into a good lather. A second shampoo is often needed.

How do you choose a good-quality castor oil?

Look for the words “virgin”, “cold-pressed” and “100% pure”, packaging in an amber glass bottle that protects it from light, and an oil that is clear, very pale yellow to amber, with no rancid smell. An oil intended for internal use must explicitly state pharmaceutical grade.

Conclusion

Castor oil is an excellent cosmetic treatment, and its richness in ricinoleic acid justifies its solid reputation for dry hair, fragile lashes and dry skin. Its most spectacular promises — faster hair growth in particular — should, however, be taken with a pinch of salt. Taken orally, it is a powerful laxative to be kept for exceptional, supervised use. Well chosen and properly dosed, it fully deserves its place in a natural routine; used incorrectly, it can cause problems.