Rosemary and castor are two of the most popular hair oils, and about as different as two oils can be. One is a light essential oil you dilute by the drop; the other is thick enough to pour slowly. Choosing between them is less about which is "better" than about your hair and what you want the oil to do.

Rosemary Oil: Light, Cooling, Scalp-Focused

Rosemary has featured in hair and scalp rituals across the Mediterranean and South Asia for centuries. It's an essential oil, which matters practically: highly concentrated, and never to be applied undiluted. Blended into a carrier it feels light and rinses out easily a comfortable choice if you dislike the heaviness of traditional oiling. 

Because it's light, it suits fine and medium hair that gets weighed down easily, and scalps that turn greasy quickly. It's usually used as a pre-wash scalp massage rather than a leave-in. Follow the directions on whichever product you choose times and amounts vary by formula. 

A pre-blended formula saves the measuring: Rosemary Hair Oil with Argan & Mint combines it with argan for smoothing and mint for a fresh scalp finish. 

Castor Oil: Thick, Rich, Length-Focused

Castor oil is roughly 90% ricinoleic acid, which gives it that unmistakable viscosity noticeably heavier than coconut, argan or almond. It coats hair rather than absorbing quickly, which is why people reach for it: it adds weight, slip and shine, and helps hair feel smoother and less prone to snapping. 

That richness makes it a natural fit for coarse, dry or tightly coiled hair, which struggles to stay moisturised. It's also popular for brows, where a little goes a long way. On fine hair it can feel greasy and flat, so thin it with a lighter oil first. 

Try Herbal Oil Castor 60ml, or the 250ml size for regular use. 

One practical caution. Castor is thick enough that overuse on long or textured hair has been linked in case reports to acute hair felting matting severe enough it can't be combed out. Use small amounts, dilute it, and comb it through rather than piling it on. 

Can You Use Both?

Yes, and for many people that's more useful than picking a side, because they work in different places. Rosemary is a scalp oil; castor is a lengths-and-ends oil. Using both covers each area without either doing the other's job. 

A simple structure: rosemary blend massaged into the scalp before washing, and a small amount of castor through mid-lengths and ends. Keep them as separate steps rather than layering both on the scalp and skip castor on the scalp entirely if you're prone to buildup or flaking, since it's occlusive enough to make both worse. 

Castor also works as a carrier for rosemary essential oil if you prefer to blend your own. 

Which Should You Choose?

Rosemary if your hair is fine or medium, your scalp gets oily, or you want something light that washes out cleanly. 

Castor if your hair is coarse, dry, coily or breakage-prone, or you want an oil for brows. 

Both if you have an oily scalp and dry ends far more common than people expect, and something no single oil handles well. 

Whichever you choose, be consistent. And patch test first: rosemary is a common contact allergen, and reactions are easier to catch on a forearm than a scalp. 

Still deciding? Our guide to choosing a hair oil for your hair type walks through it, or browse the hair care range. 

Frequently Asked Questions

What's the difference between rosemary and castor oil?

Rosemary is a light essential oil that must be diluted and is used on the scalp. Castor is a thick carrier oil applied directly to lengths and ends. 

Can you mix rosemary and castor oil?

Yes castor works as a carrier for rosemary essential oil, which needs diluting anyway. If your hair is fine, thin the castor with a lighter oil. 

Can I leave castor oil on overnight?

Check the product directions, as these vary by formula. Overnight use generally suits dry, coarse or coily hair in small amounts; on fine hair or a flake-prone scalp, a shorter pre-wash treatment is more comfortable. 

Do I need to dilute rosemary oil?

Yes undiluted essential oil can irritate the scalp. Use a pre-blended hair oil, or dilute it into a carrier oil yourself.