Castor oil for hair: does it grow hair, and is it safe to use?

Castor oil has become one of the most confident claims in hair care. It is promoted for thicker edges, fuller brows and regrowth, usually with a before-and-after photo. When you look for the human evidence, you do not find much.

This matters more than usual because castor oil has one thing most folk remedies lack: a reported case of a serious hair problem soon after use. It is rare, but it should be part of the decision.

Does castor oil grow hair?

The best summary we found is a 2022 systematic review in the Journal of Drugs in Dermatology, which covered coconut, castor and argan oil across 22 articles. On castor oil, it found weaker evidence for improving hair quality through shine, and no strong evidence supporting its use for hair growth.

That shine finding traces back to a 2003 lab study which used image analysis of treated hair. It measures how hair reflects light. It does not measure how much hair you have.

Where the growth theory comes from

The argument runs in three steps, and they have very different standing.

1. A real finding about baldness. A 2012 paper in Science Translational Medicine reported that prostaglandin D2 inhibits hair growth and is elevated in the bald scalp of men with androgenetic alopecia.
2. A computer prediction. A 2015 study used computer docking to screen compounds from 12 herbs against the enzyme that makes prostaglandin D2. Ricinoleic acid was among those predicted to inhibit it, and the authors called for lab and animal testing to follow. Ricinoleic acid makes up about 90% of the fatty acids in castor oil.
3. The leap. From there, the claim becomes "castor oil regrows hair". Nobody has shown this in an adequate human trial of castor oil.

A 2026 narrative review in Cureus described this as a possible route for castor oil in androgenetic alopecia and called for further clinical work. "Possibly" and "further work" are the important words there, and they often go missing in the retelling.

What castor oil can do

The realistic use is cosmetic. Castor oil is very viscous, and our guide to which oils penetrate treats it as a heavy sealant. A small amount, mixed with a lighter oil, can make the ends feel smoother and look shinier until the next wash. That is a modest benefit, and many other, easier oils offer the same thing.

Castor oil risks

Reviews generally describe castor oil as well tolerated on the skin, and a 2025 re-review by the US Expert Panel for Cosmetic Ingredient Safety concluded it is safe in cosmetics as currently used. Processed castor oil does not contain ricin, the toxin found in the seeds. Two risks are still worth knowing about.

Hair felting. In 2017, doctors in India reported a 20-year-old woman whose whole scalp of long hair matted into a hard mass, like a bird's nest, soon after she applied coconut and castor oil and then washed it with her usual shampoo. It was her first time using castor oil. The matting could not be undone, and she was advised to cut the hair off. She was also badly distressed, and received psychological support.

Keep this in proportion. It is one case report, coconut oil and shampoo were involved too, and so it cannot prove that castor oil was the sole cause. The authors put it down to castor oil's high viscosity combined with long hair. They also counted only 17 reported cases of acute matting worldwide, from all causes. It is rare, but the result is severe enough to justify some care if your hair is long.

Contact allergy. Allergic reactions have been reported, including from cosmetics that contain castor oil, such as lipstick. These cases are uncommon, but an itchy or swollen rash after use is a reason to stop. Scalp reactions are hard to see, so do not wait for one to become obvious.

Scalp oils may also be a poor choice for seborrhoeic dermatitis, as our hair oiling guide explains.

How to use castor oil on hair, if you still want to

1. Patch test first. Put a little on the skin behind your ear or on your inner arm, and wait a day or two.
2. Dilute it. Mix one part castor oil with several parts of a lighter oil, which makes it easier to spread and to wash out.
3. Detangle first. Start from the ends and work up. Do not apply thick oil to hair that is already knotted.
4. Use very little. A few drops on the ends is enough to judge the effect.
5. Wash gently. On long hair, keep the lengths running downwards. Do not pile them on top of your head and scrub.
6. Stop if the hair starts to clump or twist. Stop handling it, and ask a hairdresser or dermatologist for help rather than forcing a comb through.

If your aim is growth, it is also worth looking at the rosemary oil evidence, which is thin but has at least one randomised trial to discuss. Whatever you try, judge it over months, because the growth cycle means nothing shows up quickly.

The honest position

Castor oil is a thick, inexpensive oil that may add some shine to the ends. Its growth reputation is built on an interesting theory, a lot of enthusiasm and no adequate human trial. If you like how it feels, use a little, diluted, and be careful with long hair. If you are worried about hair loss, the better next step is a proper diagnosis, not another bottle.