The numerous benefits of castor oil on the skin.

Beneficial for dry skin, castor oil is primarily acclaimed for its hydrating properties, largely due to its richness in oleic acid. Naturally found in sebum, this acid is known for its film-forming action and is capable of strengthening the skin's protective hydrolipidic film. Furthermore, castor oil contains linoleic acid, an omega-6 that can insert itself between the corneocytes, the cells of the stratum corneum, and strengthen their cohesion. With better organisation, the stratum corneum is less prone to water loss.

The moisturising properties of castor oil were recently evaluated in a clinical trial involving 15 individuals with dry skin. Each volunteer was given a formulation consisting of castor oil and distilled water. A bioelectrical impedance analysis was used to provide numerical values representing the skin's moisture levels. After application for 10 days, an average improvement of 10% in skin hydration was observed, confirming the hypothesis that castor oil possesses noteworthy moisturising effects.

Sometimes used in conjunction with dermatological treatments to combat certain inflammatory skin conditions, castor oil is believed to soothe the skin. According to some studies, it appears that this vegetable oil may inhibit the activities of phospholipase A2 enzymes, some of which release arachidonic acid. Indeed, arachidonic acid is a vasodilator that exacerbates redness and irritation. Furthermore, this molecule can be metabolised into prostaglandins or leukotrienes, mediators of inflammation.

The anti-inflammatory activity of thecastor oil was also highlighted in a study conducted with rats on which paw oedema was induced. In some rats, castor oil was administered orally (500 mg/kg) 30 minutes prior. In other animals, diclofenac, a non-steroidal anti-inflammatory, was used as a reference standard. The evolution of the rats' paw volume was then monitored. After 4 hours, the volume of the oedema was 0.38 ± 0.01 mL in untreated rats, 0.14 ± 0.01 mL in rats that received castor oil, and 0.11 ± 0.01 mL in those that had diclofenac. Although this study is encouraging regarding the anti-inflammatory properties of castor oil, it would be preferable to see these results confirmed during clinical trials conducted with humans.

Naturally produced during chemical reactions at the mitochondrial chain level, but also synthesised in response to UV exposure or pollution, free radicals are unstable compounds that have an unpaired electron in their chemical structure. To stabilise themselves and gain an additional electron, they react with other molecules in the body, which can damage skin structures and accelerate the onset of wrinkles or pigmented spots. To protect against this, it is recommended to use antioxidants.

Thanks to its Vitamin E content, castor oil could provide some protection to protein fibres and cellular constituents against oxidative stress. The antioxidant activity of this plant extract was evaluated using a DPPH test. A median inhibitory concentration (IC50) of the DPPH° free radical of 19.02 µg/mL was measured for castor oil, compared to 2.36 µg/mL for ascorbic acid, whose antioxidant properties are recognised. According to this study, it would appear that castor oil is capable of combating free radicals and protecting the skin from their harmful effects.

Beyond its antioxidant action, which allows it to prevent wrinkles, castor oil could potentially act directly on the signs of ageing. This is at least what a study conducted in 2023 by PARVIZI and his team suggests. The study involved 22 individuals with crow's feet wrinkles. For two months, the volunteers applied a cream containing 10% castor oil to their eye contour area twice a day. At the end of the study, a mean improvement of 33% in the wrinkle score was measured, while no side effects were reported. It could therefore be hypothesised that castor oil may have a certain tightening effect, a hypothesis that would be good to see confirmed in further clinical trials involving more volunteers.

Some studies suggest that castor oil could accelerate the healing of minor wounds. Among them, we can mention the one carried out by MANDA and his team who were interested in a formulation based on ascorbic acid (0.5%), gum adragant (6%) and castor oil (25%). The healing effects of this cream were evaluated on rats with minor cuts (≈ 20 mm2). After application twice a day for nine days, the researchers observed an average reduction of 98% in the surface area of the treated wounds, compared to 80% for the cuts left as they were. The formulation therefore seems to have promoted tissue repair.

However, it is challenging to attribute this effect to castor oil as the cream also contained ascorbic acid, known for stimulating the activity of fibroblasts, the cells responsible for the production of scar tissue, as well as for its effects on angiogenesis. Nevertheless, we can assume that castor oil contributed to keeping the wound hydrated, which is crucial in a healing situation.

Often a source of insecurity, brown spots disrupt the uniformity of the complexion. To reduce their visibility, some people turn tocastor oil. The effectiveness of this vegetable oil in combating hyperpigmentation was recently evaluated in a study conducted with around twenty participants with pigmented dark circles. After applying it twice daily for 60 days, the participants noticed an average improvement in pigmentation of 8.2%. As brown spots, like pigmented dark circles, are due to an accumulation of melanin in the skin, it can be assumed that castor oil could help to diminish them.

At present, the mechanism at work has not yet been elucidated. However, it is suggested by some researchers that castor oil may exhibit a anti-tyrosinase activity and that this would be the source of its depigmenting properties. As a reminder, tyrosinase is an enzyme involved in the process of melanogenesis to convert tyrosine into melanin, the pigment responsible for skin colour.

Finally, castor oil appears to have a noteworthy antifungal action that can help prevent fungal infections. These can cause significant discomfort, leading to dry skin, itching, or even redness. Fungal infections are the result of fungal colonisation. Various types of fungi can cause these infections: those of the Candida genus, dermatophytes, or even Malassezia.

According to a study in vitro, castor oil could potentially inhibit the proliferation of certain fungi, such as Lentinus sajor-caju, in a dose-dependent manner. During this study, the antifungal effect of castor oil was compared to that of fluconazole, a medication commonly used to treat fungal infections. For this, the disc diffusion method, or Kirby-Bauer test, was performed. After 24 hours of incubation, a similar antifungal action was observed for the disc that received castor oil (9.6 µg) and the one that had fluconazole (100 µg). Castor oil thus appears to have a genuine antifungal effect against Lentinus sajor-caju, which could potentially extend to other fungi. Although further studies are still needed, this botanical extract could be interesting in the fight against fungal infections.

• VENKATARAMAN S. & al. Anti-inflammatory and free radical scavenging activity of Ricinus communis root extract. Journal of Ethnopharmacology (2006).

• PAULA ZURRON A. & al. Antiinflammatory activity of ricinus communis derived polymer. Brazilian Journal of Oral Sciences (2008).

• ALARAPE A. & al. Physico-chemical properties and in vitro antifungal activities of Ricinus communis seed oil against Lentinus sajor-caju. Scholars Research Library (2014).

• HIDAYAH N. & al. The Influence of Combination of Castor Oil with Aquades on Increasing Moisture over a Dry Skin. 3rd UNJ International Conference on Technical and Vocational Education and Training (2018).

• MANDA K. & al. Evaluation of wound healing potential of ascorbic acid, castor oil, and gum tragacanth formulation in murine excisional wound model. Pharmacognosy Magazine (2020).

• PARVIZI M. & al. Efficacy of castor oil cream in treating infraorbital hyperpigmentation: An exploratory single-arm clinical trial. Journal of Cosmetic Dermatology (2023).