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Does castor oil regrow hair?

We found no study that tested castor oil on its own for hair growth in people, whether on the scalp, the eyebrows or the eyelashes, and no registered trial of castor oil on its own. The only hair-growth trial we found that included it used a castor and rosemary blend, made and funded by the company that sells it. The usual explanation, that it blocks a hair-loss signal called PGD2, comes from a computer model, and a drug that blocks that pathway failed in a clinical trial.

What has been tested

A 2025 Indian trial gave 90 adults with thinning hair one of three oils for 90 days: rosemary with castor oil, rosemary with lavender, or coconut oil as the comparison. There was no castor-only group, so castor oil's part cannot be separated from rosemary's. The company that makes the products, Soulflower, funded the trial, and one author works for it. A 2022 systematic review of coconut, castor and argan oil found "no strong evidence" supporting castor oil for hair growth.

The PGD2 explanation

Bald scalp in men with androgenetic alopecia contains more prostaglandin D2 (PGD2), a molecule that slows hair growth. A 2015 study used a computer model to predict that ricinoleic acid, the main fatty acid in castor oil, might block the enzyme that makes it. We found no experiment testing that prediction in cells, animals or hair. Setipiprant, an oral drug that blocks a PGD2 receptor, was tested in a placebo-controlled trial in men with androgenetic alopecia and did no better than placebo.

Eyebrows and eyelashes

We found no study measuring eyebrow or eyelash growth with castor oil. A 2024 eye-health review warned about a TikTok trend of putting castor oil in the eyes to improve eyesight, noting that over-the-counter castor oils can contain preservatives that may irritate or harm the eye.

Hair felting

Castor oil is thick, and it has been blamed for acute hair felting, where hair suddenly mats into a hard mass that cannot be combed out. In a 2017 case report, a 20-year-old who used castor oil on her hair for the first time, alongside coconut oil, developed felting that could not be undone, and the hair had to be cut off.

Where PGD2 appears in the register

The PGD2 pathway was a real drug target. Setipiprant is in the register as discontinued: its placebo-controlled trial is the most direct test the PGD2 idea has had, and it came back negative.

In the register

Sources

  1. Rosmagain™ as a Natural Therapeutic for Hair Regrowth and Scalp Health: A Double-Blind, Randomized, Three-Armed, Placebo-Controlled Clinical Trial · Cureus, 2025 · PMID 40656290
  2. Coconut, Castor, and Argan Oil for Hair in Skin of Color Patients: A Systematic Review · Journal of Drugs in Dermatology, 2022 · PMID 35816075
  3. Prostaglandin D2 inhibits hair growth and is elevated in bald scalp of men with androgenetic alopecia · Science Translational Medicine, 2012 · PMID 22440736
  4. In silico prediction of prostaglandin D2 synthase inhibitors from herbal constituents for the treatment of hair loss · Journal of Ethnopharmacology, 2015 · PMID 26456343
  5. Setipiprant for Androgenetic Alopecia in Males: Results from a Randomized, Double-Blind, Placebo-Controlled Phase 2a Trial · Clinical, Cosmetic and Investigational Dermatology, 2021 · PMID 34703265
  6. An Emerging Ophthalmology Challenge: A Narrative Review of TikTok Trends Impacting Eye Health Among Children and Adolescents · Ophthalmology and Therapy, 2024 · PMID 38315349
  7. "Castor Oil" – The Culprit of Acute Hair Felting · International Journal of Trichology, 2017 · PMID 28932063

Checked against its sources on 2026-10-01, by us, not by a doctor. A research register, not medical advice: talk to a dermatologist about your own case. See why we're not doctors.