Disclosure: Leslie S. Baumann, MD, has disclosed the following relevant financial relationships:
Received funding for advisory boards and/or clinical research trials from: Allergan; Burt's Bees; Galderma; Johnson & Johnson,
CEO of: Skin Type Solutions Inc
Castor seed oil is derived from the seed of Ricinus communis, a plant found throughout tropical and subtropical countries. Ricinoleic acid is the main component, along with its various salts and esters, with roles that affect skin health by conditioning the skin, stabilizing emulsions, and acting as surfactants in cosmetic formulations. Other key constituents include glycerides of isoricinoleic ricinoleic, dihydroxy stearic, and stearic acids, as well as eicosanoic, linolenic, and palmitic acids. Through cold pressing of the seeds, the oil is filtered and steamed to remove the well-known toxin ricin, which does not partition into the oil. Discussions of castor oil use to treat particular skin disorders in children date back to 1885 in the literature. This column focuses on current data and uses of castor seed oil for hair and skin health.
Castor oil is among several oils that have been used traditionally by people of color, particularly those with Indian or African heritage, to treat hair and scalp conditions.
Ricinoleic acid and its metabolites active in castor seed oil are known to confer moisturizing effects on hair as well as fungicidal and germicidal activity in protecting the scalp and hair shaft. Furthermore, the fatty acids found in castor seed oil have been reported to penetrate and nourish the hair follicle. Potentially relevant for the treatment of androgenetic alopecia, ricinoleic acid has been demonstrated to penetrate skin and inhibit prostaglandin D2 synthase, thus imparting some positive influence on hair growth.
A systematic review of the literature on coconut, castor seed, and argan oils for hair in skin-of-color patients by Phong and colleagues in 2022 included 22 articles that met inclusion criteria. The investigators noted that whereas coconut oil demonstrably improves brittle hair and hair infestation, the evidence is weaker but extant on castor oil improving hair luster.
In 2006, Piamphongsant reported on the effects of a phenol-castor oil peel for melasma. Five different formulations were mixed and tested on the forearms of 10 volunteers. Formula 4 yielded an effective peel with the fewest side effects and was used to treat 30 patients, with an application time of 1 minute along with an antimelasma cream. Two cases of melasma were cleared in 1 week; some fading was seen in other cases. Melasma indices fell from 206.4 to 91.2 in the patients who received formula 4. Hyperpigmentation was observed in five individuals, and there was one case of hypopigmentation
In 2003, Carson and colleagues reported on the successful use of a castor oil-balsam of Peru-trypsin combination ointment for wound healing. Specifically, they performed a retrospective study on this treatment of skin graft donor sites in 36 consecutive patients (20 male, 16 female). After 11 days, all donor sites had epithelialized without complications or adverse effects.
In 2015, Díez-Pascual and Díez-Vicente reported on the development of a biocompatible and biodegradable castor oil-based nanocomposite film reinforced with chitosan-modified zinc oxide nanoparticles that was found in vitro to effectively achieve more rapid wound healing than neat castor oil and control gauze. The films also imparted notable antibacterial activity against Escherichia coli, Staphylococcus aureus, and Micrococcus luteus, with effects dose-dependently increasing with chitosan-zinc oxide concentration and observed to be more robust against gram-positive cells.
In 2010, Mahler and colleagues investigated the in vivo effects on the skin barrier of castor wax beads vs abrasive substances and pure detergent for occupational skin protection. Thirty healthy volunteers (15 with and 15 without a predisposition toward atopic dermatitis) applied one of three cleansing preparations (detergent, detergent containing castor wax beads, or detergent containing walnut shell powder) four times daily over 3 weeks or applied no treatment. In the group receiving the detergent with walnut shell powder, significantly greater transepidermal water loss was recorded as was more erythema in the treated region. Both cleansers with additives were found to be comparably more effective than the basic detergent. The investigators concluded that castor wax beads delivered a non-irritating quality to detergents for abrasive cleaning of resistant oily skin contamination suitable for people with atopic skin diathesis.
Of note, the Cosmetic Ingredient Review Expert Panel issued its final report on the safety of castor seed in 2007, finding it safe for use as a cosmetic ingredient.
Castor seed oil has been used traditionally to improve hair and skin health. However, data are currently insufficient on this prevalent plant seed to warrant confidence in its use. More research is necessary to establish whether some promising findings on the uses of castor seed oil can yield widespread efficacy in contributing to skin and hair health.