Last Updated: July 29, 2026
The Claim
Castor oil grows longer, thicker eyelashes and fuller brows. It's one of the oldest beauty claims in the book — and one of the most persistent. Every few years it goes viral again. So does it actually work?
What Is Castor Oil?
Castor oil is a vegetable oil pressed from the seeds of the Ricinus communis plant. It's unusually high in ricinoleic acid (approximately 90% of its fatty acid content) — a rare omega-9 fatty acid with documented anti-inflammatory and antimicrobial properties. It's also highly viscous, which gives it excellent occlusive properties.
The Evidence
Evidence tier: TIER 3 — there are no peer-reviewed RCTs demonstrating that castor oil stimulates eyelash or eyebrow growth in humans. The evidence is entirely anecdotal and mechanistic. Ricinoleic acid has anti-inflammatory properties that may support a healthy follicle environment, and the occlusive nature of castor oil may reduce lash breakage and improve appearance — but this is not the same as stimulating new growth.
Honest limitation: Castor oil may make lashes appear thicker and healthier by conditioning and reducing breakage. It does not appear to activate dormant follicles or extend the anagen phase. For actual lash and brow growth, prostaglandin analogs (like bimatoprost, the active in Latisse) have TIER 1 evidence — but require a prescription.
Is It Safe?
Generally yes, with one caveat: castor oil applied too close to the eye can cause irritation and, in rare cases, a condition called acute hair felting (where lashes become matted). Apply carefully to the lash line only, not directly to the eye. Patch test first.
Verdict: INCONCLUSIVE — Leaning Bust for Growth, Confirm for Conditioning
Castor oil won't hurt your lashes and may improve their appearance through conditioning. But if you're expecting dramatic growth, the evidence doesn't support that claim. For scalp hair growth — where the follicles are more accessible and the evidence is slightly stronger — castor oil is a reasonable addition to a hair care routine.
Evidence-Backed Alternatives for Hair Growth
The Hair Growth Oil with Tea Tree, Fenugreek & Rosemary combines rosemary (TIER 2 evidence for hair growth) with complementary botanicals. The Boost Crown Whip Scalp Tonic supports scalp circulation and follicle health. For women specifically, the Ladies Kaminomoto EX and Ladies Kaminomoto Hair Accelerator Lemon have documented efficacy for female hair loss patterns.
Disclosure: Veracil sells several of the products mentioned in this article. All product recommendations are based on ingredient science and formulation quality.
Shop This
- Hair Growth Oil with Tea Tree, Fenugreek & Rosemary — rosemary-forward hair growth oil with TIER 2 evidence
- Boost Crown Whip Scalp Tonic — scalp circulation and follicle health support
- Ladies Kaminomoto EX — extra strength formula for women's hair growth
- Ladies Kaminomoto Hair Accelerator Lemon — lemon-scented women's hair growth tonic
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