All you need to know about castor oil.

Like all vegetable oils, castor oil is composed of fatty acids, but it contains several vitamins and bioactive compounds that contribute to its skin benefits. The table below lists the molecules found in castor oil and their effects on the skin.

If the castor oil is popular in skin creams and serums due to its many benefits:

• Castor oil hydrates the skin and strengthens the skin barrier.

  Castor oil is first recognised for its moisturising properties, beneficial for dry skin. These benefits stem from its rich oleic acid content, a fatty acid present in sebum that can reinforce the hydrolipidic film. In addition, the linoleic acid in castor oil can insert between corneocytes, the cells of the stratum corneum, which promotes cellular cohesion and reduces water loss. These moisturising effects were confirmed in a clinical trial involving 15 participants with dry skin. After applying a castor oil-based formulation for 10 days, a mean increase of 10% in skin hydration was measured by bioelectrical impedance.

• Castor oil may soothe the skin and reduce irritation.

  Castor oil could help soothe sensitive or redness-prone skin. Some studies suggest this oil could inhibit the activity of phospholipase A2 enzymes, which are involved in the release of arachidonic acid, a pro-inflammatory precursor. By reducing the availability of this fatty acid, castor oil would limit the formation of prostaglandins and leukotrienes, two key mediators in the inflammatory response. However, studies to date on the anti-inflammatory properties of the castor oil have been conducted on rodents. Clinical studies are still needed to determine its potential soothing effect when applied topically.

• Castor oil helps protect the skin from oxidative stress.

  Castor oil contains vitamin E, an antioxidant molecule known for its ability to neutralise free radicals. These unstable compounds, generated by UV exposure or pollution, degrade the skin’s structural proteins and promote the premature appearance of wrinkles or pigment spots. The antioxidant activity of castor oil was assessed by a DPPH assay, with a median inhibitory concentration (IC50) measured at 19.02 µg/mL, compared with 2.36 µg/mL for ascorbic acid, used as a reference. This capacity to trap free radicals suggests that castor oil can help protect skin from the harmful effects of oxidative stress and prevent photoageing.

• Castor oil may act on wrinkles.

  A study involving 22 participants with crow’s feet suggests that castor oil may reduce wrinkles. Over two months, participants applied a cream containing 10% castor oil to the eye contour twice daily. At the end of the study, a mean improvement of 33% in wrinkle score was recorded, with no side effects reported.

• Castor oil may reduce pigmentation spots.

  Castor oil may help reduce the visibility of brown spots. A clinical trial on around twenty participants with pigmented dark circles revealed an average improvement in pigmentation of 8.2% After 60 days of twice-daily application of a 10% castor oil formulation. Although the precise mechanism remains unclear, castor oil is thought to exhibit anti-tyrosinase activity, limiting the production of melanin responsible for hyperpigmentation.

• Castor oil may prevent fungal infections.

  Castor oil appears to have a useful antifungal effect to prevent fungal infections on the skin or nails. A study compared the effect of castor oil on the fungus Cunninghamella bertholletiae, which causes certain infections, to standard antifungal agents using disc diffusion and minimum inhibitory concentration (MIC) tests. The mean inhibition zone was 22.44 mm for castor oil versus 20.66 mm for amphotericin B, with MIC values of 1.72 µg/ml for castor oil and 1.66 µg/ml for amphotericin B. These results indicate castor oil could help prevent fungal infections.

Castoroil offers numerous benefits for hair, eyelashes, eyebrows, and beard hair. Among its key attributes, it may support growth. Studies show prostaglandin D2 (PGD2), a molecule involved in hair growth inhibition, is elevated in certain forms of alopecia. Ricinoleic acid from castor oil may reduce PGD2 expression, creating an environment more conducive to growth. However, a few clinical studies exist, and more research is needed to confirm that castor oil accelerates hair and beard hair growth.

Beyond this potential effect, castor oil hydrates and nourishes hair and follicle fibres. Owing to its richness in fatty acids, it forms a protective film on their surface, limiting dehydration. As fatty acids insert into the cuticle lipids, they promote better alignment of the scales. This alignment improves light reflection, making hair shinier. Castor oil has antioxidant and antifungal properties that benefit the scalp or skin beneath the beard. Antioxidant compounds neutralise free radicals responsible for premature ageing of the hair fibre and bulb, while antifungal action helps balance the skin flora.

The castor oil is viewed with caution because of ricin, a toxin present in castor seeds. However, this concern is unfounded for topical use, as ricin is a water-soluble protein that remains in the seed cake after extraction and does not transfer into the final oil. Castor oil obtained by cold pressing or mechanical extraction undergoes a rigorous process that ensures removal of this toxin.

In topical use, castor oil has no known hazards and a favourable safety profile.

It suits sensitive skin and can be used by pregnant or breastfeeding people and young children. Its high viscosity is one of its few practical drawbacks but poses no risk. It can be bothersome for oily skin, where high sebum levels form a protective hydrolipidic film that does not benefit from a rich oil such as castor oil. Despite this, castor oil has a low comedogenicity index (1) and is not considered to promote comedone formation.