Is castor oil harmful?

Is castor oil toxic when ingested?

The castor oil, extracted from the seeds of the plant Ricinus communis, has been known since antiquity for its multiple uses. Today it appears in various fields: formulation of skincare products, lubricants, plasticisers, and as a laxative. However, despite this broad use, it raises concerns due to the presence of ricin in the seeds. Indeed, ricin is a highly toxic glycoprotein, considered one of the most potent natural poisons in the world. When ingested, ricin can cause severe gastrointestinal symptoms, such as intense abdominal pain, vomiting or diarrhoea, and lead to serious dehydration. Mortality remains low if treatment begins without delay.

To date, the literature reports some fifty cases of ricin poisoning worldwide (PubMed, ScienceDirect and Google Scholar, 1980–2020).

However, it is important to note that ricin is found mainly in raw castor seeds and is absent or present in trace amounts in the oil. When the castor oil is extracted, the processes used, such as cold-pressing, remove most of this toxin. A recent study showed that cold-pressed castor oil contains 35 ± 13 µg/L of ricin. A toxic oral dose is estimated at 1 to 5 µg per kg of body weight. Thus, ingesting 30 mL of castor oil—a common laxative dose—delivers 1 µg of ricin. This value is well below the toxic threshold.

What are the side effects of castor oil when applied topically?

The castor oil is generally well tolerated when applied to the skin.

Nevertheless, like any ingredient, it is not without risk of irritation or allergic reactions. In rare cases, castor oil has been linked to contact dermatitis. A case report describes a 30-year-old woman who had experienced lip darkening accompanied by itching and swelling for a year. After a clinical assessment and a series of patch tests, a pigmented contact dermatitis induced by ricinoleic acid was detected. The woman’s reaction was due to the castor oil in her lipstick. After she stopped wearing it, her lips returned close to their original colour.

Note : This type of reaction to castor oil is rare. In most cases, castor oil or products containing it are not associated with adverse effects. As a precaution, it is preferable to perform a test the first time you use castor oil or a new skincare product: apply a small amount to the inside of your elbow and monitor for 24 to 48 hours for any reaction. This simple practice prevents widespread reactions.

Moreover, the use of castor oil on eyelashes or eyebrows to strengthen them or promote growth is popular, but some wonder if castor oil is harmful to the eyes. To date, no scientific source shows castor oil has ocular toxicity. On the contrary, some studies have examined its benefits in managing blepharitis, an inflammation of the eyelids. Applying castor oil to the eyelid margin may reduce inflammation and ease eye dryness. We recommend limiting application and ensuring use of a clean and disinfected spoolie.

Adverse effects associated with applying castor oil to hair?

Castor oil is subject to two opposing assumptions. Some believe it stimulates hair growth, while others think it may cause hair loss. No scientific study has shown that castor oil promotes hair loss. In contrast, several studies suggest ricinoleic acid may inhibit prostaglandin D2 (PGD2) activity. This protein, together with its metabolite 15-dPGJ2, halts hair growth by binding to the molecular receptor GPR44. Castor oil may help prevent hair loss.

Scientific literature has described a rare adverse effect associated with castor oil: the acute hair felting, which refers to a tight and disorderly entanglement of hair fibres that makes detangling impossible. A 20-year-old woman, after applying castor oil combined with coconut oil to her hair for the first time, experienced sudden severe matting. After washing and an attempted drying, strands twisted and compacted into a solid mass resembling a bird’s nest. Attempts to detangle worsened the condition and caused pain. The sole solution was to cut away the mass of hair.

Acute hair matting after applying a mixture of castor oil and coconut oil.
Source: KIRUTHIKA S. et al. Castor oil – the culprit behind acute hair felting. International Journal of Trichology (2017).

Although it may seem severe, acute hair felting is a rare phenomenon : only 17 cases have been reported worldwide, all causes combined. In the vast majority of cases, castor oil poses no risk to hair. We recommend using it in moderation. A few drops of castor oil suffice to deliver its hair care benefits. Remember to wash your hair to avoid weighing it down.

Is castor oil safe to use during pregnancy?

When taken orally, castor oil has long been used to induce labour in pregnant people. After ingestion, castor oil releases ricinoleic acid through the action of intestinal lipases. It produces a potent laxative effect and promotes uterine contractions by interacting with EP3 prostanoid receptors on intestinal and uterine smooth muscle cells. In mice, removal of these receptors abolishes both the laxative effect and the contractions induced by castor oil, confirming their key role. For this reason, pregnant people sometimes avoid castor oil for fear of causing miscarriage.

Some studies highlight potential risks. A 39-year-old patient at 39 weeks’ gestation ingested 5 mL of castor oil to induce labour. She developed intense uterine contractions, membrane rupture and required an emergency caesarean section because her cervix remained closed. During surgery, a 2 cm uterine tear was discovered, requiring surgical repair. This case highlights the importance of caution with self-medication.

In a medically controlled setting, administering castor oil may help induce term labour. A double-blind study involving 200 pregnant women showed that a 60 mL dose of castor oil between the 40th and 41st week of pregnancy significantly reduced the risk of prolonged pregnancy : 17.1% of women in the intervention group went beyond term, compared with 41.5% in the control group. No maternal or neonatal complications were reported. It is important to note that these results were obtained under supervised conditions and close medical monitoring.

These effects of castor oil apply only to its oral absorption. When applied to skin or hair, it remains on the surface without systemic absorption. Topical use of castor oil is possible during pregnancy.