Quick Answer: There are no published randomized controlled trials proving castor oil promotes hair growth in humans. It’s a good hair moisturizer and coating agent that may make hair appear thicker, but claims about actual new growth are not supported by clinical evidence.
Key Takeaways
- There are no published randomized clinical trials specifically evaluating castor oil for human hair growth.
- The popular belief in castor oil for hair is largely anecdotal and driven by social media, not clinical evidence.
- Castor oil’s high viscosity may provide scalp occlusion and moisture retention, which could reduce hair breakage-but this is mechanical, not growth-stimulating.
- Ricinoleic acid makes up ~90% of castor oil’s fatty acid content and has some anti-inflammatory and antimicrobial properties that could theoretically support scalp health.
- If evaluating scalp health interventions, minoxidil (topical) has the strongest evidence for hair growth; compare against that standard.
The Hair Growth Claim
Castor oil is one of the most recommended “natural hair growth” remedies on social media. The claim is that applying castor oil to the scalp, eyelashes, or eyebrows will stimulate new hair growth, make hair thicker, and reverse thinning.
What the Evidence Shows
No clinical trials for hair growth
A 2022 systematic review by Phong et al. examining coconut, castor, and argan oil for hair found no clinical evidence supporting castor oil specifically for hair growth. The review included studies on skin of color patients and noted that while coconut oil had some evidence for treating brittle hair, castor oil’s evidence was largely absent.
No eyelash or eyebrow studies
There are zero published randomized controlled trials testing castor oil’s effect on eyelash or eyebrow growth. Every dermatologist quoted in major health outlets confirms this. The idea comes from a theoretical connection: ricinoleic acid may modulate prostaglandin pathways, and prostaglandin analogs (like bimatoprost/Latisse) are proven to grow eyelashes. But castor oil is not bimatoprost – having a tangentially related mechanism does not equal clinical proof.
What castor oil actually does for hair
Castor oil is a thick, viscous oil that physically coats the hair shaft. This can:
- Reduce moisture loss from the hair
- Add temporary shine and apparent thickness
- Smooth the cuticle and reduce frizz
- Lubricate the scalp, which may help with flaking from dryness
These are cosmetic effects, not growth effects.
Jamaican Black Castor Oil (JBCO)
JBCO is made by roasting castor beans before pressing. It has cultural significance in Caribbean hair care traditions and anecdotal support, but it has the same evidence gap as regular castor oil – no clinical trials for growth.
How to Use Castor Oil on Hair (If You Choose To)
- Apply a small amount to scalp or hair ends
- Leave on for 30 minutes to overnight
- Wash out thoroughly – castor oil is very thick and may require double-shampooing
- Mixing with a lighter oil (like jojoba or coconut) makes it easier to apply and remove
- For eyelashes/eyebrows: use a clean spoolie or cotton swab, apply a thin layer at night. Avoid getting it in your eyes.
When to See a Doctor Instead
If you’re experiencing actual hair loss or thinning, castor oil is not a treatment. Conditions like androgenetic alopecia, alopecia areata, telogen effluvium, and thyroid-related hair loss have evidence-based treatments. See a dermatologist.
The Bottom Line
Castor oil is a fine hair conditioner and moisturizer. It is not a proven hair growth treatment. If you enjoy using it as part of your hair care routine, there’s no harm in that – but adjust your expectations accordingly.
Sources:
- Phong C, et al. “Coconut, Castor, and Argan Oil for Hair in Skin of Color Patients: A Systematic Review.” J Drugs Dermatol. 2022. PMID: 35816075
- Healthline. “Castor Oil for Eyebrows.” Medically reviewed, 2018.
- StatPearls. “Castor Oil.” NCBI Bookshelf NBK551626.
Frequently Asked Questions
Does castor oil grow hair?
No clinical trial evidence supports castor oil as a hair growth treatment. Anecdotal reports are widespread, but these cannot distinguish hair growth from hair breakage reduction (which castor oil’s occlusive properties could plausibly support). The two are very different outcomes.
How do you use castor oil on hair?
A common application is massaging castor oil into the scalp and along the hair shaft, leaving it for 30-60 minutes (or overnight), then washing out. The high viscosity makes removal require multiple washes. Due to lack of clinical guidance, there is no validated protocol.
Can castor oil cause hair loss?
Heavy or frequent use can cause scalp buildup and potentially trap bacteria or yeast, worsening dandruff or folliculitis in susceptible people. Castor oil is also very difficult to remove and can cause traction on hair if dried-potentially increasing breakage. Use sparingly if at all.
What actually works for hair growth?
Minoxidil (topical 2-5%) is the OTC treatment with the strongest RCT evidence for androgenetic alopecia. Finasteride (prescription, oral) is effective for men. Addressing iron deficiency, thyroid dysfunction, or other underlying causes is essential. Scalp massage has emerging evidence in small trials. For more detail, see our related guide on castor oil safety and side effects.
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Sources
- A systematic review of the potential treatment effects of topical epidermal growth factor for ocular surface disorders. Contact lens & anterior eye : the journal of the British Contact Lens Association. 2025. PMID: 39632210.
- Plasma growth hormones, P300 event-related potential and test of variables of attention (TOVA) are important neuroendocrinological predictors of early cognitive decline in a clinical setting: evidence supported by structural equation modeling (SEM) parameter estimates. Age (Dordrecht, Netherlands). 2007. PMID: 19424831.
- FDA Cosmetics Overview
- Castor Oil Packs
- Castor Oil as Laxative
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