Castor oil for hair growth: popular, sticky and barely studied

Castor oil is one of the most talked-about home remedies for thin hair. Videos and beauty blogs recommend it for a receding hairline, sparse eyebrows, short eyelashes and slow-growing hair, often with dramatic before-and-after photos. It is cheap, sold in pharmacies and online across Malaysia, and has a long history in traditional practice in India, Africa and the Caribbean, which adds to its appeal.

This guide explains what castor oil is, the scientific theory behind the hair growth claims, what the evidence actually shows, what castor oil may do for the hair strand, and its risks, including a rare problem called acute hair felting. This is general information, not personal medical advice. For a broader look at oils, see hair oils and hair growth.

Short answer

• Castor oil is a thick plant oil made mostly of ricinoleic acid ¹. It can coat the hair strand and may improve shine and softness, which is a cosmetic effect.
• There are no good clinical trials showing that castor oil increases scalp hair growth or treats hair loss. A recent dermatology review describes a possible mechanism and calls for proper clinical studies; it does not show that castor oil works on human scalp hair ².
• The theory links castor oil to prostaglandin D2, a substance found at higher levels in balding scalp ³. A theory is not the same as a result in people.
• Castor oil is usually well tolerated, but it is not risk-free. Allergic contact dermatitis has been reported ⁴, and in one published case the whole scalp of long hair matted into a hard mass after castor and coconut oil were applied, and the hair had to be cut off ⁵.

What castor oil is

Castor oil is pressed from the seeds of the castor plant, Ricinus communis. Most of the world's supply comes from Gujarat in India, and the oil is used widely in soaps, lubricants, coatings and cosmetics ¹. The seeds themselves contain ricin, a toxin, but the oil used in cosmetics is processed so that ricin is not present in the oil.

What makes castor oil unusual is its composition. Most plant oils contain a mix of fatty acids, but castor oil is dominated by one, ricinoleic acid, which makes up the large majority of the oil ¹. Ricinoleic acid gives castor oil its thick, sticky texture, which is much heavier than coconut or olive oil.

"Jamaican black castor oil" is made by roasting the beans before extracting the oil, which makes it darker and gives it a smoky smell. It is heavily marketed for hair, but there is no good evidence that it works differently from ordinary castor oil on the scalp.

The prostaglandin theory

The main scientific argument for castor oil comes from research on prostaglandins, natural signalling molecules in the body. A 2012 study found that prostaglandin D2 (PGD2) levels were higher in the balding scalp of men with androgenetic alopecia than in their non-balding scalp, and that PGD2 slowed hair growth in laboratory and animal experiments ³. That finding prompted interest in medicines that block the PGD2 pathway.

From there, some sources argue that ricinoleic acid might reduce PGD2 and so help hair grow. A recent narrative review of castor oil in dermatology mentions this possible mechanism and also notes that castor oil may improve hair lustre, but it concludes that more clinical investigation is needed to establish whether it is effective ². In other words, there is a plausible-sounding theory, but not the controlled human trials needed to show that rubbing castor oil on the scalp changes hair growth.

It is worth remembering how many theories in hair science look promising in a dish and then fail in people. The treatments with good evidence for pattern hair loss, such as minoxidil and finasteride, were tested in large controlled trials ⁶.

What castor oil may do for the strand

Like other oils, castor oil can coat the hair surface. Some people find this makes hair look shinier, feel softer and tangle less, at least until the next wash. Because it is so thick, castor oil is often mixed with lighter oils to make it easier to spread.

Coating the hair can also make it look slightly fuller or darker for a while, and may reduce breakage from dryness in people with very dry hair. Reducing breakage can make hair look longer over time, but this is different from making more hair grow from the follicle. See hair treatments with weak evidence.

Eyebrows and eyelashes

Castor oil is widely recommended for thin eyebrows and short lashes. There is no good evidence that it makes brows or lashes grow. Prescription eyelash products work in a different way: they contain prostaglandin analogue drugs, which are medicines tested in clinical trials, and are not the same as castor oil.

If you try castor oil near the eyes, use a tiny amount on a clean applicator, keep it out of the eyes and stop if the eyelids become red, swollen or itchy. Sudden loss of eyebrows or lashes deserves a doctor's assessment, because it can be a sign of alopecia areata, thyroid problems or other conditions.

The risks

Hair felting. Acute hair felting is a rare condition in which hair suddenly twists into a hard, tangled mass that looks like a bird's nest. In a published case from South India, the patient's long scalp hair matted immediately after coconut oil and castor oil were applied following a wash. The authors suggested that castor oil's high viscosity, combined with long hair, contributed. The matting could not be undone and the hair had to be cut off, with a serious emotional impact on the patient and family ⁵. This is very uncommon, but people with long hair should be careful about rubbing thick oils in vigorously and piling hair on top of the head.

Contact dermatitis. Castor oil and its derivatives are used in many cosmetics and medical products. Although they are usually well tolerated, allergic reactions have been reported, including from castor oil-containing dressings ⁴. Itch, redness and small bumps after use are signs to stop.

Clogged, greasy scalp. Thick oil left on the scalp in a hot, humid climate can feel heavy and may worsen flaking in people prone to seborrhoeic dermatitis.

Eye irritation if the oil runs into the eyes.

Delayed treatment. The biggest risk is spending months on castor oil while a treatable cause of hair loss progresses.

How to use castor oil sensibly

If you enjoy castor oil as part of your hair care, these steps reduce the risks:

1. Patch test first on a small area of skin.
2. Use a small amount, and consider mixing it with a lighter oil to make it easier to spread.
3. Apply mainly to the lengths of the hair, especially if your scalp is oily or flaky.
4. Do not rub vigorously or pile long hair on top of your head while oiled; comb it gently.
5. Wash it out with shampoo, usually within a few hours.
6. Keep it out of your eyes.
7. Stop at once if the scalp becomes red, itchy or sore.
8. Keep it separate from minoxidil, which should be applied to a clean, dry scalp.

Hair loss needs a diagnosis

If your hairline is receding, your parting is widening or patches of hair are falling out, it is worth finding out why. Pattern hair loss, shedding after illness or stress, alopecia areata and scalp conditions all need different approaches. Treatments with much better evidence than castor oil include minoxidil and, for suitable men, finasteride. See minoxidil, male pattern baldness and hair loss treatment in Malaysia.

Life in Malaysia

Castor oil is easy to find in Malaysian pharmacies and online stores, often as plain oil or in "hair growth" blends with other herbs. Some imported products carry strong claims about growing hair. Check the label for the full ingredient list, and be cautious of products that promise to treat baldness. In Malaysia's heat and humidity, heavy oil under a helmet, cap or tudung can feel greasy and uncomfortable, so many people find it easier to use oil on wash days and wash it out the same day. Hair oiling is also a long-standing tradition in many Indian Malaysian families, and the felting case is a reminder to handle long, oiled hair gently.

Common myths

• "Castor oil grows hair on bald spots." There is no good evidence.
• "Black castor oil is stronger." There is no good evidence that it works differently.
• "It blocks the hormone that causes baldness." That is a theory, not a proven result in people.
• "Natural oils cannot harm hair." Rare felting and contact dermatitis have been reported.
• "The thicker the oil, the better it works." Thickness mainly makes it harder to wash out. See hair loss myths.

Common mistakes

• Leaving thick oil on the scalp for days.
• Rubbing oil vigorously into long hair and piling it on the head.
• Mixing castor oil into minoxidil.
• Using castor oil on a red, flaky or itchy scalp.
• Waiting months with oil alone while a hairline continues to recede.

Questions to ask your doctor

1. What type of hair loss do I have?
2. Is there any reason castor oil would be unsuitable for my scalp?
3. Could my flaking or itch be a scalp condition that needs treatment?
4. Which treatments have good evidence for my type of hair loss?
5. Can I keep oiling my hair while using minoxidil?
6. Should I have blood tests for iron, thyroid or other causes?
7. How long should I use a treatment before judging it?
8. What changes would mean I should come back sooner?

The bottom line

Castor oil is a thick, inexpensive oil that may make hair look shinier and feel softer. The hair growth claims rest on a theory about prostaglandin D2 rather than on good human trials, and a recent dermatology review calls for proper clinical studies before conclusions can be drawn. Castor oil is usually well tolerated, but contact dermatitis and rare acute hair felting have been reported. If your hair is thinning, a diagnosis and treatments with stronger evidence are the better path. See rosemary oil for hair and black seed oil for hair.

Frequently asked questions

Does castor oil make hair grow?

There are no good clinical trials showing that castor oil increases hair growth on the scalp. The claims rest mainly on a theory about prostaglandins and on personal stories.

Can castor oil treat male or female pattern hair loss?

No study has shown that castor oil treats pattern hair loss. Minoxidil, and finasteride for suitable men, have much better evidence.

What is ricinoleic acid?

Ricinoleic acid is the main fatty acid in castor oil and makes up most of it. It gives castor oil its thick, sticky texture.

Is Jamaican black castor oil better?

Jamaican black castor oil is made from roasted beans and is darker. There is no good evidence that it works better for hair than ordinary castor oil.

Can castor oil make my eyebrows or eyelashes thicker?

There is no good evidence that it does. If you try it near the eyes, use a very small amount, keep it out of the eyes and stop if the eyelids become red or itchy.

What is hair felting?

Hair felting is a rare condition where hair suddenly tangles into a hard, matted mass. A published case linked it to castor oil and coconut oil applied to long hair, and the matted hair had to be cut off.

Can castor oil irritate the skin?

It is usually well tolerated, but allergic contact dermatitis has been reported. Do a patch test and stop if the scalp becomes red, itchy or sore.

Can I use castor oil with minoxidil?

Keep them separate. Apply minoxidil to a clean, dry scalp as directed, and do not mix it with oils, which may affect how it spreads and absorbs.

Educational content. Not medical advice.