Hair, eyelashes, eyebrows, and beard: what benefits does castor oil have on hair follicles?

Derived from cold pressing of castor bean seeds (Ricinus communis), a shrub mainly grown in China, India, and Brazil, castor seed oil (INCI: Ricinus Communis (Castor) Seed Oil) is one of the most used oils for hair, eyelashes, eyebrows, and beard care. It is credited with stimulating hair growth. Many apply castor oil to their scalp, beard, or eyebrows daily to increase density or slow down hair fall.

Although limited, scientific data suggest castor oil may stimulate scalp and body hair growth.

This property of castor oil stems from its high content of ricinoleic acid, an unsaturated fatty acid that acts by inhibiting the activity of prostaglandin D2 (PGD2). This protein, in synergy with its metabolite 15-dPGJ2, halts hair growth by binding to the molecular receptor GPR44. Research on alopecia noted prostaglandin D2 levels were three times higher in bald scalp areas than in areas with hair. That’s why castor oil is sometimes cited as a natural solution to baldness and excessive hair loss.

Moreover, a study in vitro showed that castor oil can stimulate keratin synthesis, the fibrous protein that makes up most hair and fur fibers and plays a key role in their elasticity and strength. Keratin is synthesized by keratinocytes in the hair bulb under complex molecular signals, including cytokines. By modulating PGD2 release, castor oil may overcome certain limits on keratin production. By improving fiber hydration, castor oil’s fatty acids may support enzymes that assemble keratin filaments. These mechanisms may explain this oil’s effect on keratin synthesis.

Applied regularly to the roots of scalp hair, beard hair, eyelashes, or eyebrows, castor oil may increase their growth rate.

Another benefit of castor oil : it helps boost shine in hair, eyelashes, eyebrows, and the beard. Its fatty acids, including ricinoleic acid, penetrate the cuticle, the outer layer of hair fibers, and strengthen the intercellular cement. This lipid-rich matrix plays a key role in cuticle scale cohesion, or the binding of its cells. When this cement is compromised by mechanical, chemical, or environmental stressors such as UV rays, the scales lift, weakening the hair fibers and increasing water loss.

By filling microfissures and reinforcing the lipid barrier, castor oil smooths the surface of hair fibers. The cuticles align and reflect light, giving scalp hair, eyelashes, eyebrows, and beard hair increased shine. This effect applies to eyelashes, eyebrows, and beard hair because they share the same structure as scalp hair.

Due to its hydrating and nourishing properties, castor oil promotes shine in hair and body hair.

Castor oil can also protect the scalp, hair, eyelashes, eyebrows, and beard hair from oxidation. While the effects of oxidative stress on skin are documented, its impact on scalp and body hair remains overlooked. The buildup of free radicals in hair follicles is significant and can accelerate hair shedding and graying. Free radicals generated by UV rays, pollution, or tobacco smoke oxidize cuticle lipids and keratin amino acids. This lipid peroxidation reduces cuticle cohesion and increases the porosity and fiber fragility.

Rich in tocopherols and phenolic compounds, castor oil traps free radicals before they damage hair follicles and the hair fiber. This slows the aging of the hair fiber and maintains its radiance. A 2021 study examined the antioxidant properties of castor oil. Researchers performed the DPPH assay based on the reduction of the DPPH2 This assay measures the antioxidant activity of a compound. The median inhibitory concentration (IC50) was determined. It is the concentration needed to inhibit 50% of a chemical reaction. In this specific case, the IC50 reflects the antioxidant efficacy of castor oil. An IC50 of 431.73 μg/mL was measured. This value is low, indicating that a small amount of castor oil provides effective antioxidant activity.

Regular application of castor oil to hair, lashes, eyebrows, and beard can be part of a strategy of photoprotection.

Note: To date, no scientific study has shown that castor oil slows down the appearance of white hair or grey hair. However, it has been established that this oil possesses antioxidant properties, which is interesting since oxidative stress is recognized as a factor accelerating hair bleaching. Despite this, no direct evidence confirms that the application of castor oil influences the appearance of gray hair.

The castor oil is sometimes cited as a natural remedy for dandruff. Dandruff occurs when cell turnover is too rapid. If epidermal cells have not matured sufficiently, they remain clumped together and detach as white clusters, forming dandruff. The causes of dandruff are numerous and remain poorly understood, but studies suggest a link between them and the fungal proliferation of the Malassezia.

To date, no clinical study has shown castor oil to act against dandruff. Some studies have highlighted its antifungal properties and shown that the undecylenic acid in this oil acts against certain pathogens and yeasts, including Staphylococcus aureus and Klebsiella pneumoniae. No research has examined castor oil’s effect on Malassezia fungi that promote dandruff. Even though it cannot be stated that castor oil eliminates dandruff, it appears to have a certain cleansing activity, useful for caring for the scalp and beard.

If castor oil is good for all types of hair (fine hair, curly hair, frizzy hair...), its rich texture makes it particularly suitable for frizzy hair, often lacking hydration.

Castor oil can be used in various ways to care for your hair and suit your needs. If your priority is to stimulate growth, warm a few drops of castor oil between your hands, then massage your scalp using circular motions to promote absorption. Avoid applying too much: castor oil is quite viscous and may weigh down the scalp. Leave on for 30 minutes to overnight, then rinse with your regular shampoo. Note that you may need to shampoo twice to fully remove the oil. To nourish your mid-lengths, protect your hair from environmental stressors, or restore shine, apply a few drops to lengths and ends. If you leave it on overnight, consider a protective hairstyle such as a braid or a loose bun: this prevents tangles, protects your pillow, and keeps the oil in place.

One to two applications per week suffice to provide castor oil’s benefits without weighing down your hair.

Beard application follows the same principle, but we advise those with oily skin to be cautious. Even if the castor oil is not considered comedogenic, it can leave an unpleasant greasy residue when skin already produces excess sebum. In that case, leave the oil on for about thirty minutes in the evening before cleansing your face with your cleansing gel or your regular cleansing cream. For lashes and brows, the application must be precise to avoid excess build-up. Castor oil can be applied using a small fine brush or a clean spoolie, such as an empty mascara wand, at the base of the lashes or brows.

Note: It is sometimes said that using castor oil in the eyelashes is dangerous. One must indeed be cautious and remain parsimonious when applying it because using unsterilised castor oil near the eyes may lead to irritation or infection. That is why, to prevent this risk, it is recommended to apply it in small quantities, using a clean bottle brush reserved for this use. Nevertheless, if the castor oil is of quality, there are no dangers. Some studies even report that its use in the eye contour is beneficial in case of blepharitis, an inflammation of the eyelid.

• FONG P. & al. In silico prediction of prostaglandin D2 synthase inhibitors from herbal constituents for the treatment of hair loss. Journal of Ethnopharmacology (2015).

• MARWAT S. K. & al. Review - Ricinus communis - ethnomedicinal uses and pharmacological activities. Pakistan Journal of Pharmaceutical Sciences (2017).

• DONKOR A. & al. Antibacterial and antifungal activities and phytochemical profile of leaf extract from different extractants of Ricinus communis against selected pathogens. International Food Research Journal (2017).

• MIRANDA T. F. Eficácia do óleo de rícino (Ricinus Communis) no crescimento capilar. Agricultural and Food Sciences (2018).

• KPOROU E. & al. Quality, safety and activity of an ointment formulated from Butyrospermum parkii and Ricinus communis oils on rabbits hair growth. Pharmacopée et médecine traditionnelle africaine (2021).

• CHAOUCHE T. M. & al. Physicochemical parameters of oil extracted from Ricinus communis L. seeds. Journal of Natural Product Research and Application (2021).

• CRAIG J. P. & al. Randomized trial of topical periocular castor oil treatment for blepharitis. The Ocular Surface (2021).

• MESINKOVSKA N. A. & al. Coconut, castor, and argan oil for hair in skin of color patients: a systematic review. Journal of Drugs in Dermatology (2022).

• HOSSAIN J. & al. Design and evaluation of hair growth - hair fall oil formulation from botanicals. Bangladesh Pharmaceutical Journal (2024).

• ROY D. & ROY R. Exploring natural ways to maintain keratin production in hair follicles. Journal of Emerging Investigators (2024).