Castor oil is the most recommended hair oil on the internet, and the thing people recommend it for is the one thing it has never been shown to do.

It is also in my Hair Repair Oil. Both of those statements are true, and the gap between them is the whole point of this post.

What the research shows

Search the medical literature for a randomised controlled trial of castor oil for hair loss and you will find nothing. Not a weak trial, not a small one. There isn't one.

That is unusual for something this popular. Rosemary has a six month trial. Pumpkin seed oil has a 24 week trial. Rice bran extract has a 16 week trial. Castor oil, the one every video recommends, has none.

Where the growth claim comes from

Castor oil is roughly 85 to 90 percent ricinoleic acid, an unusual fatty acid you don't find in this concentration anywhere else. The argument goes that ricinoleic acid influences prostaglandin E2, which is involved in the hair growth cycle.

That part is real. Ricinoleic acid does interact with those pathways in laboratory conditions, and prostaglandin E2 is genuinely part of follicle cycling.

But there is a long distance between a molecule doing something in a dish and that oil growing hair on your head. Every castor oil growth claim you have seen is built on crossing that distance without evidence.

What it genuinely does, which is not nothing

Here is where castor oil earns its place.

It is an exceptional emollient. It coats the strand, limits moisture loss, and supports elasticity better than almost anything else available. Hair that stretches instead of snapping keeps its length.

And that matters more than people realise. A lot of what looks like hair loss is breakage. Length you lose to snapping is length you never see, no matter how well your follicles are performing.

So castor oil does not grow hair faster. It helps you keep what you grow. For most people that produces a similar visible result, which is probably why the myth has survived so long.

The risk nobody puts in the caption

Castor oil is thick. Considerably thicker than any other oil in common use.

There are documented medical case reports of acute hair felting, also called plica neuropathica, following castor oil use. The hair mats together into a solid tangle that cannot be combed out. In the reported cases the only fix was cutting it off.

It is rare, and it is associated with heavy application of undiluted oil, usually on long, fine or textured hair. But it is real and it is in the literature, and I have never once seen it mentioned by an account telling you to slather it on overnight.

Contact dermatitis and folliculitis also turn up in the reports. Patch test if your skin reacts to things.

How to use it properly

• Dilute it. Roughly one part castor to three parts of a lighter oil. Undiluted castor is difficult to wash out and that is where most problems start.
• Mid-lengths and ends. This is the opposite of my usual advice, and that is deliberate. You are treating the hair shaft, not the follicle.
• Pre-wash treatment. Twenty to thirty minutes, then shampoo out.
• Don't leave raw castor on overnight, particularly if your hair is long or fine.
• Judge it on breakage, not growth. Look at your ends and your brush, not your parting.

So why is it in my formula?

Because diluted castor oil in a balanced blend is genuinely good for elasticity, and because dilution is the entire safety issue solved.

In the Hair Repair Oil, castor sits at a working proportion alongside lighter oils, with rosemary, pumpkin seed oil and rice bran extract carrying the follicle side of the formula. Those three have human trial data. Castor is not there to grow your hair. It is there so that what grows survives being brushed.

That is a smaller claim than the internet makes. It is also one I can stand behind.

Motiya products are cosmetics, not medical treatments. This article is general information and not medical advice. If your hair loss came on suddenly, comes with scalp pain or visible bald patches, or is worrying you, please speak to your doctor or a dermatologist.

Maryam is a hairstylist in Mississauga with a diploma in haircare formulation from Formula Botanica. She formulates every Motiya product herself.