Castor oil is a natural plant oil obtained from the seed of the castor plant. The castor seed, or bean, is the source of numerous economically important products as one of the world's most important industrial oils, and was one of the earliest commercial products. Castor beans have been found in ancient Egyptian tombs dating
The castor plant, whose botanical name is Ricinus communis, is native to the Ethiopian region of east Africa. It now grows in tropical and warm temperate regions throughout the world and is becoming an abundant weed in the southwestern United States. Castor plants grow along stream banks, river beds, bottom lands, and in almost any warm area where the soil is well drained and with sufficient nutrients and moisture to sustain growth. They are annuals that can grow 6–15 ft (1.8–5 m) tall in one season with full sunlight, heat, and moisture. The tropical leaves, with five to nine pointed, finger-like lobes, may be 4–30 in (10–76 cm) across. Flowers occur on the plant (which is monoecious, meaning that there are separate male and female flowers on the same individual), during most of the year in dense terminal clusters, with female flowers just above the male flowers. Each female flower consists of a spiny ovary, which develops into the fruit or seed capsule, and a bright red structure with feathery branches (stigma lobes) to receive pollen from the male flowers. Each male flower consists of a cluster of many stamens that shed pollen that is distributed by wind. The spiny seed pod or capsule is composed of three sections, or carpels, that split apart at maturity. Each carpel contains a single seed. As the carpel dries and splits open, the seed is ejected, often with considerable force. The seeds are slightly larger than pinto beans and are covered with intricate mottled designs, none of which have exactly the same pattern due to genetic variations. At one end of the seed is a small spongy structure called the caruncle, which aids in the absorption of water when the seeds are planted.
The name "castor" was given to the plant by English traders who confused its oil with the oil of another shrub, Vitex agnus—Castus, which the Spanish and Portuguese in Jamaica called agno-casto. The scientific name of the plant was given by the eighteenth-century Swedish naturalist Carolus Linnaeus. Ricinus is the Latin word for tick; apparently Linnaeus thought the castor bean looked like a tick, especially a tick in engorged with blood, with the caruncle of the bean resembling the tick's head. Communis means "common" in Latin. Castor plants were already commonly naturalized in many parts of the world by the eighteenth century.
There are several cultivated varieties of the castor plant, all of which have striking foliage colorations. The castor plant grows rapidly with little care and produces lush tropical foliage. Its use as a cultivated plant should be discouraged because its seeds or beans are extremely poisonous. Children should be taught to recognize and avoid the plant and its seeds, especially in the southwestern United States where it grows wild near residential areas. Flower heads can be snipped off of castor plants as a protective measure.
The active poison in the castor bean is ricin, a deadly water-soluble protein called a lectin. The ricin is left in the meal or cake after the oil is extracted from the bean, so castor oil does not contain any of the poison. The seed is only toxic if the outer shell is broken or chewed. Humans and horses are most susceptible to ricin, although all pets and livestock should be kept away from the castor seed. It has been estimated that gram for gram, ricin is 6,000 times more deadly than cyanide and 12,000 times more deadly than rattlesnake venom. A dose of only 70 grams, or one two-millionth of an ounce (roughly equivalent to the weight of a single grain of table salt) is enough to kill a 160-pound person. Even small particles in open sores or in the eyes may be fatal. As few as four ingested seeds can kill an adult human. Lesser amounts may result in vomiting, severe abdominal pain, diarrhea, increased heart rate, profuse sweating, and convulsions. Signs of toxicity occur about 18–24 hours after ingestion. Ricin seems to cause clumping (agglutination) and breakdown (hemolysis) of red blood cells, hemorrhaging in the digestive tract, and damage to the liver and kidneys.
Ricin has attracted considerable attention as of early 2003 because of its association with terrorist groups. Although ricin cannot easily be used against large groups of people, it has been used to assassinate individuals by injection. The Centers for Disease Control and Prevention (CDC) considers ricin a B-list bioterrorism agent, meaning that it is relatively easy to make and is considered a moderate threat to life.
On the positive side, ricin is being investigated as a tool for cancer treatment. A promising use is the production of an immunotoxin in which the protein ricin is joined to monoclonal antibodies. The ricin-antibody conjugate, which is produced in a test tube, should theoretically travel directly to the site of a tumor, where the ricin can destroy the tumor cells without damaging other cells in the patient.
Castor oil is a strong and effective cathartic or purgative (laxative), with components in the oil that affect both the small and large intestines. It has been used to clear the bowels after food poisoning and to relieve constipation. It is sometimes used in hospitals to prepare the patient's abdomen for x rays of the colon or kidneys. Castor oil is classified as a stimulant laxative, also known as a contact laxative. This type of laxative encourages bowel movements by acting on the intestinal wall, increasing the muscle contractions that move along the stool mass. Stimulants are a popular type of laxative for self-treatment, but unfortunately are more likely to cause side effects. There are milder types of laxatives that may be more useful for inducing regularity and treating constipation. Generally laxatives should be used to provide short-term relief only, unless otherwise directed by a doctor.
Castor oil is frequently used in animal experiments to test the effects of new medications on the gastrointestinal tract.
If castor oil has been prescribed by a doctor, his or her instructions for the timing and quantity of doses should be followed. For self-treatment, users should follow the manufacturer's instructions. At least 6–8 glasses (8 oz each) of liquids should be taken each day to soften the stools. Castor oil is usually taken on an empty stomach for rapid effect. Because results usually occur within two to six hours, castor oil is not usually taken late in the day. The unpleasant taste of castor oil may be improved by chilling it in the refrigerator for at least an hour. It may then be stirred into a glass of cold orange juice. Flavored preparations of castor oil are also available.
Castor oil is also used topically to treat corns. The oil is applied once or twice daily directly to the corns, which are surrounded with adhesive-backed corn aperture pads made of felt to hold the oil. The corns are then covered with hypoallergenic silk tape. After soaking with the castor oil, the corns will be softened for removal with a pumice stone. Castor oil can be used in a similar manner to remove warts. Castor oil is also used to treat ring-worm, abscesses, bruises, dry skin, dermatitis, sunburn, open sores, and other skin conditions. Additional less well-known uses of castor oil include hair tonics, cosmetics, and contraceptive creams and jellies.
For menstrual cramping, especially when fibroids may be present or when flows are heavy, castor oil packs may be placed on the abdomen for up to an hour. The packs are made by soaking square or rectangular pieces of cotton, cotton flannel, or undyed wool 2–4 in (5–10 cm) thick with 4–6 oz 118–177 ml) of castor oil. The pack is folded over once or twice, placed directly on the abdomen, and covered with plastic wrap. Over the pack, a water bottle or a heating pad on a low setting may be used to keep the pack warm. After use, the skin may be cleansed with a warm solution of baking soda and water (2 tsp of baking soda to 1 qt water). Some herbal therapists maintain that castor oil packs may aid in shrinking small fibroids. Castor oil packs have also been used in the treatment of many other diseases and disorders, including breast pain, digestive tract problems, abscesses, hemorrhoids, wounds, and gallstones.
Castor oil and its derivatives also are used in many industrial products, including paint and varnish, fabric coatings and protective coverings, insulation, food containers, soap, ink, plastics, brake fluids, insecticidal oils, and guns. It is a primary raw material for the production of nylon and other synthetic resins and fibers, and a basic ingredient in racing motor oil for high-performance automobile and motorcycle engines. Castor oil is also used as a fuel additive for two-cycle engines, imparting a distinctive aroma to their exhaust. Even though it is malodorous and distasteful, it is the source of several synthetic flower scents and fruit flavors.
Castor oil for medicinal purposes is pressed from the seeds of the castor plant and is slightly yellow or colorless. It has a lingering nauseating aftertaste, even though peppermint or fruit juices are sometimes added as flavor enhancers in an attempt to disguise its disagreeable taste. Castor oil is available in both oil and emulsified liquid preparations.
Castor oil should not be used by a pregnant woman, as it can cause contractions. Castor oil should not be used if a patient is hypersensitive to the castor bean; or has an intestinal obstruction, abdominal pain, cramping, bloating, soreness, nausea, vomiting, fecal impaction, or any signs of appendicitis or an inflamed bowel. It should not be used by anyone for more than a week unless a doctor has ordered otherwise. Overuse of a laxative may lead to dependence on it. Any sudden changes in bowel habits or function that last longer than two weeks should be checked by a doctor before using a laxative.
Children up to the age of six should not take a laxative unless prescribed by a doctor. In older adults, the use
Side effects of castor oil that require medical attention include:
There are other less serious side effects that are less common and may go away as the patient's body adjusts to the castor oil. These side effects include belching, cramping, diarrhea, and nausea. If they do continue or are bothersome, the person should check with a doctor. In addition, because castor oil causes a complete emptying of the contents of the intestine, patients should be advised that they may not have another bowel movement for two to three days after a dose of castor oil.
Patients should not take castor oil within two hours of taking other types of medicine, because the desired effect of the other medicine may be reduced. Patients who are taking digitalis, digoxin, or a diuretic should consult their physician before taking castor oil, as the castor oil may intensify the effects of these drugs by causing the body to lose potassium.
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Centers for Disease Control and Prevention (CDC). 1600 Clifton Road, Atlanta, GA 30333. (404) 639-3311. <www.cdc.gov>.
National Digestive Diseases Information Clearinghouse. National Institute of Diabetes and Digestive and Kidney Disease. National Institutes of Health. 2 Information Way. Bethesda, MD 20892-3570. (310) 654-3810.
Rebecca J. Frey, PhD