As it turns out, all of those expensive celeb-backed eyebrow and eyelash growth products you might have tried might not actually be necessary. According to eyebrow expert Azi Sacks, the one product our brows and lashes need the most is actually castor oil, and specifically this now-$10 bottle from Amazon.

"It's like Rogaine for your brows," Sacks tells InStyle. "With continued use, you'll see a change in your brows in just three weeks. They'll become thicker and fuller."

Kate Blanc Cosmetics Castor Oil

A lot of lash and brow growth products on the market dry out your hair and cause it to snap, Sacks explains. So while you're gaining growth in some areas, at the same time, you're actually shedding in others. Once you stop using these serums, your hair will likely be left more coarse and less soft than when you began, she says.

What makes castor oil so much better is its ability to "stimulate hair growth and moisturize the area under hair to create a stable environment," Sacks says. So you're not just getting surface-level hydration, but something deeper and longer-lasting.

Plus, the Kate Blanc Cosmetics castor oil that Sacks recommends is simple to use. For your lashes, put one drop onto each of your ring fingers and rub it together before gently dabbing your hair. For your brows, you can use the included spoolie for application or repeat the same ring-finger process. The product can also be used along your hairline to prevent thinning, or as a spot treatment on stubborn blemishes. She says it'll feel a little heavy at first, so using it at night before bedtime is a comfortable way to implement this step into your beauty routine.

Sacks isn't the only one who loves this affordable treatment — more than to 73,400 people have given the castor oil a five-star rating. If only every beauty product in our cabinets came with that acclaim.