Does castor oil really treat inflammation, skin, hair and constipation?

Castor oil is broken down by pancreatic enzymes in the small intestine, releasing glycerol and ricinoleic acid². Ricinoleic acid then specifically activates the EP3 prostaglandin receptor. In mice lacking EP3 receptors, castor oil's laxative effect and its ability to contract the uterus are absent, and the effect depends on EP3 receptors in smooth-muscle cells³. Although ricinoleic acid is chemically similar to prostaglandin E1, it did not show the same physiological properties in the safety assessment².

Ricinoleic acid's anti-inflammatory effect, seen in animal models, works differently. When it is applied to the skin repeatedly for several days, it reduced experimentally induced swelling in mice and guinea pigs, and lowered tissue levels of substance P, a pain and inflammation neuropeptide. Its effects resemble those of capsaicin, the hot compound in chili peppers, but without the burning sensation, so the authors describe it as a possible capsaicin-like, non-pungent anti-inflammatory agent¹. The first, single application actually increased swelling, so the effect appears only with repeated use. These findings are from animals; they do not show that castor oil reduces inflammation in people.

Castor Oil Packs

One of the most traditional applications is the castor oil pack — a cloth soaked in castor oil, placed over the abdomen or liver area, often with gentle heat. Practitioners report benefits, but there is almost no clinical research on packs. See our castor oil packs page for what the single study found, and for the cautions about heat and pregnancy.

Constipation and Labor

Castor oil is classified by the FDA as generally recognized as safe and effective for use as a stimulant laxative². The mechanism was clarified in 2012, when researchers showed that ricinoleic acid acts on EP3 receptors in intestinal smooth-muscle cells³. The same pathway contracts the uterus, which is why swallowing castor oil has been used to induce labor and why pregnant women should not take it unsupervised³.

Skin and Hair

Castor oil and its derivatives function primarily as skin-conditioning agents, emulsion stabilizers, and surfactants in cosmetics, and castor oil and ricinoleic acid can also help other chemicals penetrate the skin². For hair, castor oil is widely used in folk practice, but the evidence for hair growth is not there: a survey of home remedies used for hair and scalp problems in the West Bank documents what people use, not whether it works⁴.

The cosmetic-ingredient safety assessment² reports that castor oil is made by cold pressing the seeds and then clarifying the oil with heat, and that castor oil does not contain ricin, because ricin does not partition into the oil. It describes these ingredients as not acute toxicants; a National Toxicology Program subchronic oral study giving castor oil at up to 10% of the diet of rats was not toxic. Undiluted castor oil was severely irritating to rabbit skin in one study but only slightly or mildly irritating in others, and ricinoleic acid caused well-defined redness at intact and abraded skin sites in one rabbit study, so patch-testing a new product is sensible.

What the Research Shows

The laxative mechanism of ricinoleic acid is well established at the receptor level in mice³. Its anti-inflammatory effect has been shown in animal models and resembles capsaicin's¹. The safety assessment found a low toxicity profile in animal and cosmetic-use data². The gaps are in human studies: there are few clinical trials for specific applications like castor oil packs and hair growth, where traditional use far outpaces formal study⁴.