Castor oil for hair, brows and lashes: real or hype?

Castor oil is one of the most shared "grow your hair and lashes" tips online. It is a thick, sticky plant oil that can make hair look shinier and feel smoother. What it has not shown, in studies on people, is that it makes hair, brows or lashes grow.

Quick answer: Castor oil for hair can coat and smooth strands, which may reduce breakage and help you keep length. There are no clinical studies in people showing it grows hair, brows or lashes. Use small amounts on the lengths or as a pre-wash treatment, keep it out of your eyes, and see a dermatologist for real thinning.

What castor oil is

Castor oil is pressed from the seeds of the castor plant. A dermatology review notes that about 90% of its fatty acids are ricinoleic acid, an unusual fatty acid that makes the oil very thick and sticky. On ingredient lists it often appears as ricinus communis seed oil. It belongs to the wider group of plant oils.

Jamaican black castor oil is made by roasting the seeds before pressing. It is darker and smells smoky. There is no research showing it works better for hair than regular castor oil; some people simply prefer its feel.

Does castor oil make hair grow?

Not according to current evidence. A dermatology review of castor oil found that hair-care claims are mostly cultural and "have not been studied to show clinical efficacy". A Cleveland Clinic dermatologist also notes that there is no data showing that applying pure castor oil to the hair promotes growth.

Where does the idea come from? Lab research suggests ricinoleic acid can block an enzyme that makes a substance (prostaglandin D2) found at higher levels in scalps with pattern hair loss. That is an interesting lead, but it comes from preclinical work, not from people using castor oil.

What castor oil can do is make hair look and feel better:

• Seal and smooth. A thick coat reduces friction, so dry and damaged hair may break less. Less breakage can mean you keep more length, which can look like growth.
• Add shine. The oil coats the surface and reflects light.
• Soften coarse hair. Many people with coily hair like it as a sealing oil.

How to use castor oil on hair

As a pre-wash treatment

1. Mix one part castor oil with two or three parts of a lighter oil, such as jojoba or argan. This makes it easier to spread and wash out.
2. Apply to the lengths and ends of dry or damp hair. Work through gently with your fingers, not a brush.
3. Leave on for 30 minutes to a few hours.
4. Shampoo out. Thick oils often need two rounds of shampoo.

To seal the ends

After your leave-in, rub one or two drops between your palms and smooth over the ends.

On the scalp

Some people like oil on a dry scalp. Cleveland Clinic notes that castor oil on the scalp can clog pores and cause irritation. If you have dandruff or seborrheic dermatitis (a flaky, itchy, red scalp), ask a dermatologist before oiling your scalp.

Brows: what to expect

There are no good studies on castor oil for brow growth. If you want to try it, use a tiny amount with a clean spoolie at night, only on the brow hairs. Stop if you notice bumps, redness or itching. Over-plucked brows may take months to regrow on their own, and some may not come back.

Lashes: be careful

There is no evidence that castor oil grows lashes. Oils near the eye can cause stinging, redness and blurry vision, and anything applied to the lash line can carry bacteria. If you try it:

• Use a clean, single-use applicator.
• Apply a tiny amount to the base of the upper lashes only, not inside the eye.
• Stop if your eyes become red, itchy, swollen or watery.

A medicine called bimatoprost is FDA-approved for growing thin eyelashes. It needs a prescription and has its own side effects, such as darkening of the eyelid skin and, rarely, permanent darkening of the colored part of the eye. Lashes return to their previous state when it is stopped. Talk to your doctor or eye doctor if you are interested.

Risks and side effects

• Eye irritation when used near the lashes.
• Skin reactions. Contact dermatitis (an itchy rash) to castor oil is reported, most often from cosmetics. Patch test on your inner arm for a few days before using it widely.
• Hair felting. A case report describes a young woman whose long hair suddenly matted into a hard, tangled mass after washing with castor and coconut oil. The hair could not be untangled and had to be cut. This is rare, but very thick oils on long hair carry this small risk.
• Clogged pores and breakouts along the hairline and forehead.
• Build-up. On fine hair or low porosity hair, castor oil can leave strands limp and greasy.

What not to combine

• Castor oil and hair-loss medicines applied at the same time. If you use minoxidil or another scalp treatment, ask your doctor or pharmacist how to fit oils around it.
• Heavy oiling on a flaking or inflamed scalp without advice.
• Thick oils on very long hair that tangles easily, because of the small felting risk.

Proven options for thinning hair

If your hair is truly thinning, castor oil is unlikely to help. Options with real evidence include minoxidil (sold over the counter for pattern hair loss) and prescription treatments chosen by a doctor. The right choice depends on the cause, which is why a diagnosis comes first. See thinning hair.

When to see a dermatologist

• Thinning hair, a widening part, or bald patches
• Brows or lashes falling out, especially in patches
• Sudden heavy shedding
• An itchy, scaly or painful scalp
• Eye pain, swelling or vision changes after using anything near the eyes (see an eye doctor promptly)

Causes such as thyroid problems, low iron and alopecia areata (an autoimmune type of hair loss) can be diagnosed and often treated.

FAQ

Is Jamaican black castor oil better for hair growth?

There is no evidence that it grows hair better than regular castor oil. Choose based on feel and smell.

Can I leave castor oil in overnight?

On the lengths, yes, with a scarf or old pillowcase. Wash it out well the next day, and keep it diluted if your hair is long.

Will castor oil thicken my hair?

It can make each strand feel coated and look glossier, but it has not been shown to make more hair grow.

Is castor oil safe for children's hair?

Keep it away from children's eyes and use only small amounts. It is not needed for children's hair growth.

Sources

• Use of castor oil in dermatology: a narrative review (PubMed Central, NIH)
• "Castor oil": the culprit of acute hair felting (PubMed Central, NIH)
• No, castor oil can't solve all (or any) of your health problems (Cleveland Clinic)
• Bimatoprost ophthalmic solution 0.03% prescribing information (US FDA)
• Hair loss: diagnosis and treatment (American Academy of Dermatology)