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

Derived from the cold pressing of common castor seeds (Ricinus communis), a shrub mainly cultivated in China, India and Brazil, the castor oil (INCI: Ricinus Communis (Castor) Seed Oil) is among the oils most used for hair, eyelash, eyebrow and beard care. It is credited with stimulating hair and body hair growth. Many people apply castor oil daily to the castor oil on their scalp, beard or eyebrows in the hope of increasing density or slow down hair fall.

Although limited, some scientific data suggest that castor oil may stimulate head and body hair growth.

This property of castor oil appears to stem 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 GPR44 molecular receptor. In studies on alopecia, prostaglandin D2 was found to be three times more abundant 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.

Another study in vitro showed that castor oil may stimulate keratin synthesis, this fibrous protein constitutes most hair fibres and shafts and plays a key role in elasticity and strength of hair and fur. Keratin is synthesised by keratinocytes in the hair bulb under complex molecular signals involving cytokines. By modulating PGD2 release, castor oil may lift certain limitations on keratin production. By strengthening fibre hydration, its fatty acids may create an environment favourable to the enzymes that assemble keratin filaments. These mechanisms may explain the oil’s effect on keratin synthesis.

When applied regularly at the roots of hair, beard hair, eyelashes or eyebrows, castor oil may result in a slight increase in growth.

Another advantage of castor oil : it enhances shine in hair, eyelashes, eyebrows and facial hair. Its richness in fatty acids, ricinoleic acid among others, enables penetration into the cuticle, the outer layer of hair fibres, and strengthens intercellular cement. This lipid matrix plays a key role in the cohesion of cuticle scales, that is its cells. When this cement is compromised by mechanical, chemical or environmental factors, such as UV rays, the scales lift, weakening the hair fibre and increasing water loss.

By filling microfissures and reinforcing the lipid barrier, castor oil smooths the surface of the hair fibre. The cuticles lie flat and reflect light, increasing shine on hair and follicles. This effect applies to scalp hair, eyelashes, eyebrows, and beard, as they share the same structure.

Castor oil’s hydrating and nourishing properties enhance the shine of hair and body hair.

Castor oil can also protect the scalp, hair, eyelashes, eyebrows and beard hair against oxidation. While the effects of oxidative stress on the skin are now well documented, its consequences for hair and hair-bearing structures remain overlooked. The accumulation of free radicals in hair follicles is not trivial and can accelerate hair loss and its greying. Moreover, free radicals generated by UV radiation, pollution or tobacco smoke oxidise cuticle lipids and keratin amino acids. This lipid peroxidation causes a loss of cohesion in the cuticle and increases the porosity and fibre fragility.

Due to its high content of tocopherols and phenolic compounds, castor oil traps free radicals before they damage hair follicles and fibres, slowing fibre ageing and preserving shine. A 2021 study investigated the antioxidant properties of castor oil. Researchers performed the DPPH assay, which relies on the reduction of the DPPH• radical to DPPH2 This allows the measurement of a compound’s antioxidant activity. The median inhibitory concentration (IC50) was determined. This is the concentration required to inhibit 50% of a chemical reaction. In this case, the IC50 reflects the antioxidant efficacy of castor oil. An IC50 of 431.73 μg/mL was measured. This value is low, which means that a small amount of castor oil provides effective antioxidant activity.

Regular application of castor oil to hair, eyelashes, eyebrows and beard may be integrated into a photoprotection strategy 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 cited as a natural treatment for dandruff. Dandruff appears when cell turnover is too rapid. If epidermal cells have not reached full maturity, they clump together and detach as white flakes, forming dandruff. The causes of dandruff are varied and not understood, but studies suggest a link between them and fungal proliferation of the Malassezia.

To date, no clinical study has shown that castor oil is effective against dandruff. However, some research has 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. In contrast, no research has been conducted on the effect of castor oil on fungi of the Malassezia type Malassezia that promote dandruff. Although it cannot be stated that castor oil eliminates dandruff, it appears to have a cleansing action useful for scalp and beard care.

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 several 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 palms, then massage your scalp using circular motions to promote absorption. Avoid using too much: castor oil is thick and can weigh down the scalp. Leave on for 30 minutes up to one night, then rinse with your regular shampoo. You may need two washes to remove all oil. To nourish lengths, shield hair from external stressors, or restore shine, apply a few drops to lengths and ends. If you leave the oil on overnight, secure hair in a protective style such as a braid or loose bun: this prevents tangles, protects your pillow, and keeps the oil in place.

One to two applications per week are sufficient to provide the benefits of castor oil without weighing down hair.

Application to the beard follows the same principle, but we advise those with oily skin to be cautious. Even if the castor oil is not regarded as comedogenic, but it can leave an unpleasant greasy residue when the skin produces excess sebum. In that case, we recommend leaving the oil on for thirty minutes in the evening before cleansing your face with your cleansing gel or your usual cleansing cream. For lashes and brows, application must be precise to avoid excessive buildup. Castor oil can be applied using a small brush or clean spoolie, such as an empty mascara spoolie, 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.

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