There is no published RCT showing castor oil grows new hair on a human scalp. The ricinoleic acid in castor binds prostaglandin receptors in the same family that experimental hair growth drugs target, which is the mechanistic hook, but the clinical step has not been confirmed. Cultural and anecdotal use is widespread and may reflect real effects we have not measured yet. Honest framing is: maybe yes, but not proven.

It will condition them, making each hair feel thicker, look shinier, and reflect more light. That can read visually as growth. Whether it stimulates actual new hair production in the brow or lash line has not been shown in controlled trials. The conditioning benefit is real and worth using.

Topical cosmetic use is generally considered safe. The historical use of oral castor oil to induce labour is a different scenario at a much higher dose. Hair oils and cleansing balms with castor oil are fine to continue during pregnancy.

The hydroxyl group on ricinoleic acid creates hydrogen bonds between molecules. Most plant oils slide past each other. Castor sticks to itself, which makes it viscous and slow to absorb. This is exactly what makes it useful as a seal but uncomfortable as a daily moisturiser on its own.

Same plant, roasted beans. The roasting raises the ash content and shifts the colour to a dark brown or black. The pH is slightly higher than cold pressed castor (around 6 to 7 vs 4 to 5). The differences are small. Both work as conditioners and sealants. The Jamaican variant has a longstanding cultural place in Black hair care.

Rarely, and only at high concentration applied generously to long fine hair with vigorous massage. The case reports describe extreme matting that sometimes required cutting out. Using castor oil pre blended into a carrier (as in the Revival oil) at normal application volumes does not cause this.