Isa's Castor Oil Journey

Castor Oil vs Rosemary Oil: Which Does What

Sep 16 2026
Isa Coelho

Rosemary oil is the hair oil everyone is talking about right now, and castor oil is the one everyone has been talking about for years. They get compared constantly, usually by people selling one of them. They're not really competitors. They're different categories of thing, and the honest answer is that most people who want both should use both.

They aren't the same kind of oil

This is the distinction that clears up most of the confusion. Castor oil is a carrier oil, pressed from a seed, thick enough to use on its own. Rosemary oil is an essential oil, steam-distilled from leaves, concentrated enough that using it undiluted on your scalp is a bad idea.

So the question isn't which one. It's what each is for.

What the evidence says about each

Rosemary oil has the stronger evidence for hair, and it's worth being precise about how strong. One frequently cited trial compared rosemary oil against minoxidil 2% in androgenetic alopecia and found comparable results at six months. That's a real trial with a real comparator, which is more than castor oil has. It's also one study, on one condition, and results took months.

Castor oil has no clinical evidence for hair growth at all. What it has is an obvious physical effect: it's thick and it coats, so hair breaks less. That's conditioning, not growth, and we've been consistent about that in our piece on thinning hair.

If you're asking purely "which one has research behind it for growth," the answer is rosemary. We sell castor oil and that's still the answer.

What each one actually feels like

Castor oil is heavy and slow. It sits on the hair and scalp for hours, which is why it works as a pre-wash treatment and why it needs a real shampoo to come out. Left in, it weighs hair down.

Rosemary oil is the opposite: a few drops, no weight, and a strong herbal smell that some people love and some find medicinal. It doesn't condition anything on its own, because there's barely any of it.

Using them together, which is what most people should do

This is the practical answer. Rosemary essential oil needs a carrier, and castor oil is a carrier. Putting a few drops of rosemary into a castor blend gives you the conditioning from one and whatever benefit the other offers, in a single step.

A sane starting ratio: one part castor oil to two parts a lighter carrier like jojoba, then three to five drops of rosemary essential oil per tablespoon of the finished blend. Never apply rosemary essential oil neat to your scalp. Patch test the blend before you commit to it.

We go into carrier ratios properly in what to blend with castor oil.

Which to pick if you're only picking one

Dry, brittle, breaking hair: castor oil. That's a conditioning problem and conditioning is what it does.
Thinning where you can see scalp: rosemary oil has the trial behind it. Also worth seeing a dermatologist, because thinning has causes worth identifying.
Dry or flaky scalp: castor oil, as a pre-wash treatment.
You want both: blend them. That's the intended use of an essential oil anyway.

One caution on rosemary

Essential oils are potent. Rosemary can irritate skin undiluted, and it's generally advised against during pregnancy and for people with epilepsy. If you're unsure, ask a pharmacist rather than a comment section.

Frequently asked questions

Is rosemary oil or castor oil better for hair?

They do different jobs. Rosemary has the stronger evidence for growth, with one trial comparing it favourably to minoxidil 2%. Castor oil has no growth evidence but conditions well. Many people blend them.

Can you mix rosemary oil and castor oil?

Yes, and it's the standard way to use rosemary. Three to five drops of rosemary essential oil per tablespoon of carrier blend. Never apply rosemary neat.

Does castor oil work as well as rosemary oil for hair growth?

No. There's no clinical evidence castor oil grows hair. Rosemary has at least one real trial behind it. Castor oil's benefit is conditioning and reduced breakage.