Another theory, she says, revolves around rosemary oil’s anti-inflammatory and antimicrobial properties, which could possibly help support a “healthy scalp environment.” (An inflamed scalp can weaken hair follicles and potentially result in shedding.)

While there is no direct link between castor oil and hair growth, dermatologists say it has other benefits. "Castor oil contains ingredients such as ricinoleic acid and fatty acids that have a moisturizing and nourishing effect on the hair," says Dr. Lori Ramirez, a Utah-based dermatologist.

The ultimate guide to hair oils for hair growth, including their exact benefits, how to use them, and the products the pros swear by for long, lush strands.

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