Glossary
A thick, pale yellow vegetable oil cold-pressed from the seeds of the Ricinus communis plant. Castor oil is composed of approximately 90 percent ricinoleic acid, an unusual fatty acid that gives it unique anti-inflammatory, antimicrobial, and humectant properties. It is used in skincare, hair care, and as a base in many cosmetic formulations.
Unlike most plant oils that are dominated by oleic, linoleic, or linolenic acids, castor oil is approximately 90 percent ricinoleic acid, a monounsaturated fatty acid found in almost no other natural source. Ricinoleic acid gives castor oil its distinctive thick, sticky texture and its impressive biological activity.
Research has shown that ricinoleic acid has significant anti-inflammatory properties, comparable in some studies to the nonsteroidal anti-inflammatory drug capsaicin. It also demonstrates antimicrobial activity against several bacteria and fungi, and acts as a potent humectant, drawing moisture from the air into the skin.
In skincare, castor oil is most commonly used as a component in oil cleansing formulations, cuticle oils, and rich moisturizers for extremely dry skin. Its thickness makes it inappropriate as a standalone facial moisturizer for most skin types, but blended with lighter oils, it adds excellent moisture retention.
Castor oil is perhaps best known in the natural beauty community for its purported hair growth benefits. While scientific evidence specifically confirming castor oil promotes hair growth is limited, the ricinoleic acid does increase blood flow to hair follicles, and the oil's humectant properties help maintain hair moisture and reduce breakage.
Castor oil has a comedogenic rating of 1 out of 5, which is relatively low. However, its thick texture means it should be used in moderation on the face. Blending with lighter oils like jojoba or using it as part of an oil cleansing method (where it is washed off) minimizes any pore-clogging risk.
Many people report thicker-appearing eyelashes and eyebrows with regular castor oil application. While rigorous clinical studies are limited, the moisturizing effect of ricinoleic acid does help prevent eyelash breakage, which can make lashes appear fuller and longer over time.
Castor oil is generally well-tolerated, but its potency means a patch test is recommended for first-time users. Some people find that the high ricinoleic acid concentration can cause irritation if applied to large areas of sensitive or broken skin.
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