Does Castor Oil Make Hair Grow?

Researched and written by Curl Centric. Read by an AI voice.

We followed the castor oil claim back to where it started. Then we tell you what castor oil has actually been shown to do for your hair.

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The full guide, with every source: Castor oil for hair growth.

Transcript

This is Curl Science by Curl Centric.

If you've ever rubbed castor oil into your edges and waited for them to fill in, you're in good company. Castor oil might be the most trusted hair growth oil there is, and videos of people's results have millions of views. So we went looking for the research showing that castor oil grows hair. What we found surprised us, and it changes how you should use the oil.

Let's start with where it comes from. Castor oil is pressed from the seeds of the castor plant. The seeds are speckled like a bird's egg, and they grow inside spiky pods.

Those same seeds contain ricin, a powerful plant poison. That sounds alarming, but properly processed castor oil doesn't contain ricin. According to the CDC, the ricin stays behind in the leftover mash when the oil is pressed out.

What makes castor oil unusual is what's in it. About 90 percent of it is one fatty acid called ricinoleic acid, which is unusual among oils sold for hair. It's also much thicker than most oils you would put on your curls.

So where does the idea that it grows hair come from? We followed the claim back, and it starts with a real discovery about hair loss. In 2012, researchers found that the bald areas of men with pattern hair loss contained more of a chemical called prostaglandin D2, a messenger the body makes in the skin. In laboratory tests, that chemical slowed hair growth.

Three years later, in 2015, a different team ran a computer simulation. They tested 389 plant compounds against a digital model of the enzyme that makes prostaglandin D2 to see which compounds might fit into it and block it. Ricinoleic acid, the main fatty acid in castor oil, was one of five compounds the computer flagged as worth testing.

And that's where the trail stops. The computer made a prediction. We couldn't find a follow-up study confirming that prediction in cells or people. But the prediction gets repeated as if it were a proven result.

In 2022, a team of researchers reviewed the studies on castor, coconut, and argan oil for hair. Twenty-two studies made the cut. For castor oil, they found no strong evidence that it helps hair grow.

We found one newer human trial that included castor oil. In 2025, a company that sells hair oil funded a study of a rosemary-and-castor-oil blend on people with thinning hair, and the study reported large improvements. But the castor oil was mixed with rosemary oil, and the blend was compared with coconut oil instead of an untreated group. So the study can't tell us what castor oil did on its own.

So what does castor oil actually do? Here's what has been measured. In a 2003 laboratory study, researchers shone light on bundles of hair and measured their shine. Castor oil made the hair shinier.

Its thickness may have a downside, though. In 2017, doctors in India described a 20-year-old woman who put coconut oil and castor oil on her hair. It was her first time using castor oil, and she hoped it would help her hair grow.

She washed her hair, and while it was drying, the ends began twisting together. Every time she tried to detangle it, the hair curled tighter until it became one hard mass the doctors compared to a bird's nest. It couldn't be undone, and the matted hair had to be cut off.

This is extremely rare. At the time of that report, the doctors said only 17 cases of sudden matting had been reported worldwide from any cause. They believed the thickness of the castor oil, combined with her long hair, contributed to this case. Still, it's a good reason to use a small amount, especially if your hair is long, dense, or tangles easily.

Now here's the part of the oil story that gets far less attention. The strongest research on oils isn't about growing hair at all. It's about what happens inside each strand when you wash it.

Every time your hair gets wet, it absorbs water and swells. Then it shrinks again as it dries. Over many washes, that repeated swelling and shrinking can wear the strand down. Scientists call this hygral fatigue.

In 2001, researchers examined thin cross sections of oiled hair to see where the oil went. Coconut oil had moved inside the strand. Mineral oil stayed on the surface. The researchers concluded that coconut oil may limit swelling and provide better protection from hygral fatigue.

Two years later, some of the same researchers measured how much protein - the material your hair is made from - washed out of the strand. Used before or after shampooing, coconut oil reduced protein loss from healthy and damaged hair. Sunflower oil and mineral oil didn't have the same effect.

And in 2024, a study found that several plant oils moved into the thin layer that holds your hair's cells together, almost like mortar between bricks. Hair treated with those oils survived more rounds of stress before breaking.

Castor oil wasn't included in those studies, so they don't tell us whether it penetrates or protects your strands the same way. What has been measured is the shine it adds when it coats your hair.

So here's the honest answer. Castor oil hasn't been shown to make hair grow from the root. And we don't yet have direct evidence that it prevents breakage. What it can do is coat your strands and make them look shinier.

If you love castor oil, you don't have to stop using it. Just use it for the job the research supports. Smooth a few drops over your ends for shine, and work it through gently. With castor oil, more isn't better, especially if your curls are long, dense, or prone to tangles.

If you want an oil that has been shown to protect your hair during wash day, coconut oil has the most research behind it, whether you use it before or after you shampoo. If any oil makes your scalp itch, burn, or break out, stop using it. And if your hair is actually thinning, see a dermatologist, because that's a different problem with different treatments.

Keeping your length is what this whole show is about, so we wrote a free guide on it. It walks you through the seven most common causes of breakage and a weekly routine that helps you reduce it. You can get it at curlcentric.com/keep-the-length, and the link is in the show notes.

That's it for this episode. If it helped, follow Curl Science in your podcast app so the next one reaches you, and leave us a rating while you're there. Curl Science is researched and written by the Curl Centric team, and it's read by an AI voice.