Castor Oil for Hair: What It Can and Can't Do

Short answer: Castor oil can make hair look shinier, but there's no strong evidence that it makes hair grow. A 2022 systematic review of 22 articles found weaker evidence for improved luster and no strong evidence for growth. S01 The growth theory comes from lab and computer studies on a hair-loss signal called prostaglandin D2, not from trials in people. S02 S03 S04 Castor oil is considered safe in cosmetics, but it's thick enough to tangle long hair badly in rare cases. S05 S06 If your hair is thinning, finding the cause matters more than any oil. S07

Castor oil is one of the most-shared hair "hacks" online, especially for edges, brows and lashes. Here's what the research supports, where the hype comes from and how to use it well.

What castor oil is

Castor oil comes from the seeds of the castor plant, Ricinus communis, and has a long history in traditional medicine and cosmetics. S02 Its signature fatty acid is ricinoleic acid, and the oil is unusually thick and viscous. S05 S06 In beauty products, castor oil and its relatives work mainly as skin-conditioning agents, emulsion stabilizers and cleansing ingredients. S06

Does castor oil make hair grow?

The honest answer is that it hasn't been shown to.

The most useful summary is a 2022 systematic review in the Journal of Drugs in Dermatology. The authors looked at coconut, castor and argan oil, three oils with deep roots in Indian and African hair traditions. Across 22 articles, they found no strong evidence that castor oil helps hair grow. S01 They also noted that many dermatologists tell patients to keep using hair oils because they don't expect side effects, not because the oils are proven to work. S01

Our hair growth oils comparison puts castor next to rosemary, pumpkin seed and peppermint oil, which have more human or animal data.

Where the growth claim comes from

The theory links castor oil to a molecule called prostaglandin D2 (PGD2).

• PGD2 and baldness: A 2012 study found PGD2, and the enzyme that makes it, at higher levels in bald scalp than haired scalp in men with hereditary hair loss. PGD2 slowed hair growth in human follicles in the lab and in mice. S04
• Ricinoleic acid as a blocker: A 2015 computer study screened 389 plant compounds for their fit with the enzyme that makes PGD2. Ricinoleic acid was one of the compounds predicted to block it. S03
• The gap: That was a prediction from computer modeling. It doesn't show that castor oil on your scalp lowers PGD2 or regrows hair. A 2026 dermatology review describes castor oil as possibly helping hereditary hair loss this way, and calls for more clinical research to establish whether it works. S02

So the idea is plausible on paper, but it isn't proven in people.

What castor oil can do for hair

The better-supported benefit is cosmetic. The 2022 review found weaker evidence that castor oil improves hair luster, and the 2026 review agreed it may improve shine. S01 S02 Its thickness can help smooth the hair surface and coat dry ends, which may make hair feel softer and look glossier.

That's a real reason to use it if you like the finish. Just keep expectations to shine and feel, not new growth.

Castor oil vs other hair oils

The 2022 review compared castor oil with two other popular oils, and the results differ. S01

• Coconut oil had the most support of the three. It has been shown to help brittle hair and to treat hair infestation, though evidence on growth is limited. S01
• Castor oil had weaker evidence for shine and no strong evidence for growth or infestations. S01
• Argan oil had no significant evidence for growth, hair quality or infestations. S01

If shine is your main goal, castor oil is a reasonable choice. If your hair breaks easily, coconut oil has more research behind it. Castor oil is also much thicker than most hair oils, which affects how you should apply it, as the next sections explain. S05

Is castor oil safe for hair?

For most people, yes. A 2025 safety re-review by the Cosmetic Ingredient Review expert panel concluded that castor seed oil and ricinoleic acid are safe as cosmetic ingredients in the ways and concentrations they're used. S06 The 2026 review also describes castor oil as generally well tolerated. S02

There are two rare problems to know about.

Hair felting

Acute hair felting is a rare condition where hair suddenly twists into a hard, tangled mass. In one case report, a person's whole scalp matted immediately after she applied coconut and castor oil following a wash. The authors blamed castor oil's high viscosity combined with very long hair. The matting couldn't be undone, and the hair had to be cut off. S05 The 2026 review lists hair felting among castor oil's rare side effects. S02

Skin reactions

Contact dermatitis, an itchy rash where a product touches the skin, has been reported. S02 Try a small amount on your inner arm first. Our guide to patch testing at home walks through it.

How to use castor oil on hair

No study has set the "right" way to use castor oil, so treat these as practical tips rather than proven protocols.

1. Patch test first. Wait a day or two to check for a reaction.
2. Use a little. Start with a few drops warmed between your palms. Castor oil is thick, so a small amount goes a long way.
3. Consider thinning it. Many people mix it with a lighter oil to make it easier to spread and rinse.
4. Focus on the lengths and ends if your goal is shine and softness.
5. Don't rub it roughly through long hair. Smooth it on in sections rather than piling hair on top of your head and scrubbing, given the felting reports. S05
6. Shampoo it out. A pre-wash treatment lets you rinse off the stickiness. You may need to shampoo twice.

If you want something else to try, rice water is another popular rinse, and our rice water guide covers what it does and doesn't do.

Castor oil for eyebrows and lashes

Brows and lashes are a big part of the castor oil trend, but there's no clinical evidence that it grows them. The reviews above found no strong evidence that castor oil grows hair, and brow or lash growth hasn't been shown in clinical trials. S01 S02 If you like how it conditions brows, use a clean spoolie and a tiny amount, and keep it out of your eyes.

If your hair is thinning

Hair thinning has many causes, including hormones, genetics, recent childbirth, illness, nutrient gaps and tight hairstyles. The American Academy of Dermatology says effective treatment starts with finding the cause. A board-certified dermatologist can examine your scalp and may order blood tests or a scalp biopsy. S07

Treatments with stronger evidence than castor oil include minoxidil, which can help early hair loss. If you stop using it, you lose the benefit. S07 Prescription options, steroid injections, platelet-rich plasma, laser devices and microneedling may also be offered, depending on the cause. S07 For gentler daily care, our guide to shampoo for thinning hair covers ingredients worth looking for.

Frequently asked questions

Does castor oil make hair grow?

There's no strong evidence that it does. A 2022 systematic review of 22 articles found no strong evidence for castor oil and hair growth. A lab theory about prostaglandin D2 exists, but it hasn't been tested in clinical trials.

What is castor oil actually good for in hair?

Mostly shine and feel. The same 2022 review found weaker evidence that castor oil improves hair luster. Its thickness can help smooth the hair surface and coat dry ends.

How long should I leave castor oil in my hair?

No study sets a time. Many people use it as a pre-wash treatment for 30 minutes to a few hours before shampooing. Use a small amount, mixed with a lighter oil if you like, and avoid piling it onto long, freshly washed hair.

Can castor oil damage hair?

Rarely. A case report describes sudden severe matting, called hair felting, after castor and coconut oil were applied to long hair, and the matted hair had to be cut. Contact dermatitis has also been reported. Patch test first and use small amounts.

Is castor oil good for eyebrows and lashes?

There's no clinical evidence that it grows brows or lashes. If you try it, use a tiny amount and keep it out of your eyes.