IN SHORT: Castor oil is an ingredient used in chemotherapy to make cancer drugs soluble. But experts agree there is no evidence suggesting castor oil has anti-cancer properties or could be used as a cure.
In footage that has been viewed thousands of times on Facebook and TikTok, a woman suggests that a castor oil compress can "break up" lumps associated with breast cancer.
She is Barbara O'Neill, the controversial Australian naturopath.
O'Neill was banned for life from providing any health services in Australia in 2019. This followed an official investigation that found she gave dangerous health advice without any qualifications or membership of a recognised health organisation.
Despite the ban, videos of O'Neill lecturing and talking about using castor oil as a cancer treatment continue to circulate on social media.
Videos of O'Neill making the claim also appeared elsewhere, like on TikTok here, here and here, and on YouTube here, here and here.
But does this claim have scientific backing? We checked.
The many uses of castor oil
Castor oil comes from the bean of a large plant that is widely grown for industrial use. The plant contains the powerful poison ricin, which is fatal in small doses.
According to this 2017 journal article, castor oil was recommended as a treatment at least as far back as 200CE, when it was thought that breast cancer was caused by too much "black bile" in the body. It has been used as a traditional medicine for many years.
Today, castor oil is a common ingredient in beauty products, and is used for dry skin or as a massage oil. Medically, castor oil is recognised by the European Medical Agency (EMA) and the US Food and Drug Administration as a stimulant laxative. Research also shows it may be effective in inducing labour.
However, a comprehensive assessment of the medical properties of castor oil by the EMA, carried out in 2016 and updated in 2023, found no evidence of any medical benefits beyond its use as a laxative.
If ingested, castor oil can also cause a number of side effects, including dizziness, diarrhoea and abdominal cramps, nausea, and low blood pressure. As it can induce labour, it is not safe to take during pregnancy.
The kernel of truth in castor beans?
A mixture containing a form of castor oil is used in some chemotherapy treatments. Chemotherapy is the use of powerful chemicals to kill fast-growing cells in the body, most often used to target cancers. However, here it is added as an ingredient to make the drug soluble for use in injections, rather than working as an anti-cancer agent itself.
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A 2007 safety report on castor derivatives from the American College of Toxicology described a 1992 study that evaluated the effects of a castor oil extract injected into mice with cancerous tumours. The study found that the extract suppressed tumours in some mice. But this was a small study done more than two decades ago, not in humans, not with castor oil, and not involving direct application to the skin. This means that it can't tell us anything about any anti-cancer effects of castor oil.
Breast cancer experts agree. Dr Liana Roodt, a Cape Town-based surgeon specialising in breast cancer care, told Africa Check "there is absolutely no evidence to support castor oil as a treatment for breast cancer".
Africa Check also contacted Reach for Recovery, a group that provides support and advice to people with breast cancer in South Africa.
"There are many challenges in sharing the correct facts and data on breast cancer," Stephné Jacobs, the chair of the Reach for Recovery board, said.
Dr Ilse De Kock, also a board member and a medical doctor, told Africa Check that the organisation would not endorse untested products for the treatment of cancer, saying "these claims are not true and have not been proven".
