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Castor oil and other extracts of the castor plant are natural supplements with many benefits such as pain reduction, digestive aid, and more. Its uses span from the traditional healers of India to the modern day cosmetics industry. Read on to discover all its benefits, uses, and side effects.

What Is Castor Oil?

Castor oil is a pale yellow viscous fluid derived from the castor bean plant (Ricinus communis). While different parts of the plant have specific health benefits, the bean of the plant is the most commonly used [R, R].  

The castor bean plant has a long history as a traditional medicine. It was used by the ancient Egyptians as an ointment for wounds, and by the Greeks and Romans as a laxative. Now, castor oil and its derivatives are common ingredients in medicine, cosmetics, soap, and even biodiesel [R, R, R].

Castor oil is mostly produced through cold pressing and purification in India, with limited production in the United States. Because ricin (a lectin), one of the most toxic natural substances, is relatively easy to extract from the castor bean plant, there are safety barriers to mass production in the U.S. and the European Union [R, R, R].

Components of Castor Oil

Castor oil consists of 90% ricinoleic, 4% linoleic, 3% oleic, 1% stearic, and <1% linolenic fatty acids; the oil content is influenced by environment and genetic factors [R, R].

The most unique aspect of castor oil is the ricinoleic acid (hydroxy fatty acid), which makes up 90% of the fat in castor oil. It is one of few naturally occurring glycerides that is nearly a pure compound [R, R].

The oil made from castor beans has a unique structure that gives it its interesting properties. Different parts of its structure (double bonds, ester linkages, and a hydroxyl group)  are sites for potential reactions. Additionally, the presence of ricinoleic acid makes this oil very versatile (high viscosity and specific gravity, and mixes with alcohol) [R].

Jamaican Black Castor Oil vs. Regular Castor Oil

Jamaican black castor oil is less pure than the regular version. This is because the main ingredient for Jamaican black castor oil is ash, a byproduct of roasting castor beans. The ash in the oil makes it less sticky and easier to apply.

Jamaican black castor oil is purported to have many benefits such as stimulating hair growth, softening hair, providing hair nutrients, and preventing dandruff. However, there are no scientific studies supporting these claims.

The vitamin E in Jamaican black castor oil also supposedly improves skin health and is used for healing wounds. Black Jamaican castor oil is sold commercially in stores and can also be ordered online.

Mechanism of Action

Castor oil has a laxative effect and causes uterus contractions through the action of the ricinoleic acid. This is the most active component in castor oil. While much is still not known about how this compound works, evidence indicates the laxative effects are from activating hormonal (prostaglandin) receptors (EP3) [R, R, R, R].

Health Benefits of Castor Oil

1) Castor Oil and Inducing Labor

An observational study that asked women  considered the efficacy of castor oil for inducing labor in 40 women. The women who received castor oil treatment (60 mL dose) had a higher chance of birth within 24 hours. Another retrospective study analyzed 323 women who received castor oil to induce labor. 91% of these women gave birth vaginally without any complications [R, R].

Similarly, 60 mL of castor oil increased the likelihood of entering labor but only for women who had given birth before and were past their due date. This might be related to the fact that inducing labor in women who have given birth before is easier (RCT of 81 pregnant women) [R].

However, a study with 612 women 40-weeks pregnant (RCT) found no significant effect of castor oil on the induction of birth [R].

In one case, ingesting 5 ml of castor oil caused a uterine rupture and severe abdominal pains in the case of a woman 39 weeks pregnant. A C-section was done 45 minutes later due to further complications (repetitive variable decelerations). But castor oil was generally safe in other studies [R]

2) Castor Oil Alleviates Constipation

Numerous studies confirm the efficacy of castor oil as a laxative. Castor oil packs (wool or cotton soaked in castor oil) are used to treat constipation in some hospitals in the US. 35 elderly patients with chronic constipation treated with castor oil packs experienced fewer symptoms of constipation. In additional studies, constipated elderly women who underwent castor oil aromatherapy had improved bowel movements [R, R].

3) Castor Oil Can Alleviate Arthritis Symptoms

Individuals with symptoms of knee arthritis were supplemented with either castor oil capsules (0.9mL) or diclofenac sodium capsules (50 mg) three times a day for four weeks (DB-RCT with 100 participants). Both capsules were significantly effective in the treatment of osteoarthritis, with no side effects caused by castor oil [R].

4) Castor Oil Reduces Pain From Shock Therapy

A prospective study (SB-RCT) evaluated 60 patients with different bone problems who received shock therapy (extracorporeal shock waves). Compared to vaseline and ultrasound gel, castor oil caused the most significant reduction in pain experienced during therapy [R].

5) Castor Oil and Skin Health

In general, there is little clinical evidence confirming that castor oil alone helps skin healing and reduces the appearance of scars.

Compounds in castor oil (tannins, flavonoids, triterpenoids, and sesquiterpenes) can possibly promote the healing process of wounds and are usually used in ointments mixed with other compounds [R, R, R].

These compounds may also increase the viability of collagen fibers by strengthening them. This increases circulation in the area prevents additional cell damage and boosts DNA synthesis [R, R].

6) Castor Oil and Hair Growth/Texture

Castor oil is also thought to improve hair growth and texture due to its effects on collagen but there is limited clinical evidence of this benefit [R, R].

An image analysis was conducted on four samples of hair to examine pigmentation and the luster (soft glow) of hair. Similar to other cosmetic oils (phenyl trimethicone and amodimethicone), castor oil was found to increase hair luster (shininess) [R].

However, in one case, one day of castor oil and coconut oil application to the hair of a 20-year-old woman caused a rare disorder of the scalp, hair felting. In this condition, hair becomes twisted and entangled, and the thickness (high viscosity) of castor oil attributed to this [R].

Animal and Cellular Studies

The following studies were conducted only on animal models and cell lines.

7) Castor Oil and Cancer

Castor oil blocked the growth of tumors in mice with cancer. Another study using cells showed that tumor cells are more sensitive to lectin (derived from castor oil) than normal cells [R, R].  

8) Castor Oil May Reduce Inflammation

Mice and guinea pigs experienced reduced inflammation after topical application of ricinoleic acid (the main component of castor oil) [R].

9) Castor Oil As An Antibacterial

A study evaluated the use of castor oil and sodium hypochlorite for disinfecting dentures. A 10% castor oil solution eliminated B. subtilis and reduced cell counts for multiple other bacterial species but was ineffective against E. faecalis [R].

Side Effects

Ricin

Generally, the production of castor oil is difficult because the castor seed is very poisonous. This is because of a toxic protein named ricin, which is found in the seeds. This protein blocks protein synthesis in cells, causing cell death. However, castor oil should not contain any ricin [R, R].

The dangers of the castor seed are outlined in the case of a 30-year woman, who had a severe allergic response (anaphylactic shock) after biting into a castor seed. She later recovered in hospital after treatment with anti-allergy drugs (antihistamines) and other drugs (corticosteroids and nebulized adrenaline) [R].

Digestive Side Effects

Castor oil causes side effects like abdominal cramping, vomiting, nausea, fainting, and insomnia, most of which are caused by increased bowel contractions. Asides from these side effects, ricin ingestion from castor seeds is lethal due to its toxicity [R, R].

Castor oil is recognized as being generally safe for use as a laxative by the FDA [R].

Allergic Reactions

Castor oil can cause an allergic reaction of the skin, called contact dermatitis. It is not considered a significant skin irritant but may cause reactions in susceptible individuals (with occupational dermatoses) [R].

A case-study looked at the effects of a hairspray that contained sulfonated castor oil. During this two-year period, 12 cases of dermatitis associated with its use were reported. A follow-up study revealed it causes allergic irritation [R].

A study involving 202 patients with inflamed lips (eczematous cheilitis) found that ricinoleic acid (a major component of castor oil) in lipsticks was the most common allergen. Additionally,  this lipstick caused an allergic response on the lips (hyperpigmentation) in a 30-year-old woman. Ricinoleic acid is also known to cause contact dermatitis [R, R].

Limitations and Caveats

Most studies with castor oil have been performed on animals and cells. This makes it difficult to understand how the drug might work in humans. Additionally, research on castor oil and its effects on and in the body are very limited.

Many of the claims as to castor oil’s benefits come from laboratories and research organizations in India — the largest exporter of castor oil. However, many of these claims have not been confirmed by additional scientific studies.

Natural Sources and Supplementation

There are a number of castor oil available commercially in-store and online. Some of these include organic castor oil, regular castor oil, and black Jamaican castor oil.

Dosage

According to the Food and Agricultural Organization and World Health Organization, castor oil ingestion is safe up to 0-0.7 mg/kg body weight per day. In order to induce labor, a dose of 60 mL seemed to be successful based on the experiments. There is not enough data for the other conditions to be able to recommend any dosages [R].  

User Experiences

Many people tout the benefits of castor oil and its closely related products. In India, people claim that it dampens the pain of birth, increases lactation, and cures stomach aches.

Many use castor oil to grow, strengthen, and replenish hair. They state their hair grows faster, more shiny, and stronger.

Some use castor oil to reduce acne and signs of aging. They state it noticeably reduces the amount of acne and wrinkles.

Most users were satisfied with castor oil and other castor bean plant products.

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