Castor oil is a vegetable oil made by pressing the seeds of the castor plant, which is native to India. The oil has a distinctive taste, and has been used as a home remedy for hundreds of years, reputedly good for everything from constipation to back pain. It is also widely used for industrial purposes.
Generally recognised as a safe and effective over the counter laxative, castor oil works for this purpose by causing contractions in the smooth muscle wall of the small intestine. Ricinoleic acid, the main active ingredient in castor oil, also causes contractions in the uterus, and castor oil may help to bring on labour in pregnant women.
Ricinoleic acid binds to prostaglandin receptors, which means that it can be a useful addition to pharmaceutical drugs, and indeed it is found in a variety of common medications. However, castor seeds are also the source of the deadly toxin ricin. Although castor oil is safe to consume, some people find that it causes stomach upsets and nausea.
Castor oil is rich in vitamin E and omega-6. It is known to stimulate blood flow to the skin surface, and has been a common ingredient in skin care products over the decades. Anecdotal evidence suggests that castor oil may be useful as a treatment for acne.