Time and time again, Helen Mirren has proven that age is irrelevant. She was named an ambassador to L'Oréal Paris in 2014 and walked the runway at Paris Fashion Week earlier this year at the age of 76. One reason behind her lifelong success is a strong sense of moxie — whether she's sporting pink hair on the red carpet, wearing sneakers to movie premieres, or frolicking down the runway barefoot, she's never taken herself too seriously. Mirren approaches her beauty routine in the same way, as evidenced by this cheeky caption she posted to Instagram: "Things I like… Castor oil, not for its laxative properties, but for hair, skin, and nails in tiny amounts.

The vegetable oil has been used in hair products for its nutrients, but we were surprised to see the Dame apply it on her skin and nails as well. That's why we consulted with a professional to find out how the affordable drugstore beauty product works.

"Castor oil is filled with omega-6, omega-9, and vitamin E, which all have nourishing and hydrating factors," Dr. Marina Peredo, a New York City-based dermatologist and founder of Skinfluence, tells InStyle."It is also an anti-inflammatory and antibacterial, and has humectant properties, which means it attracts moisture and keeps the skin hydrated." And since it contains triglycerides, the vegetable oil helps retain moisture and prevents drying on the body. For all these reasons, she says that it can soften skin and cuticles, moisturize nail beds, and promote healthy nail growth.

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While the oil helps with achieving shiny hair and preventing split ends, too, Dr. Peredo says that "hair growth from castor oil is controversial" because there is little supportive scientific literature on the topic. She also recommends that people who are acne-prone avoid using it on their skin or hair as it can cause breakouts.

Want to follow in Dame Helen's footsteps? Head to Amazon to pick up this highly-rated best-selling organic castor oil and use it in small amounts for lustrous hair, hydrated skin, and healthy nails.