Jamaican black castor oil benefits for your eyebrows: Regular plucking, waxing and tinting of our eyebrows weakens the hair follicle and thins them over the years. Castor oil improves blood circulation and helps strengthen the hair shaft by locking in moisture, and the oil’s essential fatty acids nourish the roots of the hair. With so many great benefits, it is no surprise that this oil is such a popular eyebrow treatment. Hexane Free.