Why does castor oil sound like something you might dab under the hood of your car to quiet a squeaky timing belt, or something a badass witch might give you to ward off evil spirits trying to come for you when you haven't called for them? I do not know. Castor oil is a yellowish oil pressed from the castor bean which—twist—is not a bean at all but is actually a seed. (Also: If you ever encounter castor "beans" do not eat them, they are poison, thank you. And yes, they are non-toxic when cold-pressed, which is the only way you will likely encounter them, thanks again.) But what castor oil definitely can do is quench dry strands and potentially stimulate healthy hair growth (although not more hair growth). We tapped the experts to get more intel.
Castor oil is a natural moisturizer for your hair.
If you look at the molecular structure of castor oil—and why would you (lol)—you'd see that it was a glycerol with a long-chain fatty acid. Why does that matter to you? Fatty acids are very good at nourishing the hair follicles, explains Atlanta-based dermatologist Tiffany L. Clay. The outer layer of the hair shaft is covered in tessellating scale-like structures called cuticles, and when the hair is damaged, those are flayed and flared, which results in both frizz and dullness. "Castor oil can seal and allow the cuticle to lie flatter," continues Clay. Like coconut oil and many other botanical oil, castor oil is very good at this job.
If you'd like to explore this application, Clay recommends warming a a very small amount between your palms and smoothing it along your ends, weekly. Because, buyer beware: Castor oil isn't exactly a lightweight oil. Castor oil is thicc and using too much can leave the hair slick or greasy; some reports even suggest the compound can lead to felting or matting. Another less intense option is finding a hair product that contains castor oil, like a shampoo, conditioner, mask, or serum, and working it into your regular hair care routine.
But castor oil can't make your hair grow (as far as we know).
Look, the internet will tell you anything you want to hear, and we want to believe it, too. We want it to be true that a relatively inexpensive little oil could make your hair grow Princess Jasmine thick. Unfortunately, we asked science, and science said nah.
"There is some proposed benefit of castor oil with improving penetration of topicals and even hair growth," says Dhaval G. Bhanusali, a New York City-based dermatologist who specializes in hair loss. "That being said, I don't think the scientific evidence is there to make any sizable claims, particularly for stimulating new hairs."
If you think of your scalp like a garden, you'll agree that keeping a garden well-watered and fertilized will yield cuter tomatoes than one that's dusty and untended. So yes, castor oil will keep your scalp hydrated and nourished, and the resulting hairs will be stronger, shinier, and healthier. But there will not be more of them, and that's an important distinction.
That said, the inefficacy of castor oil in stimulating novel hair growth shouldn't leave you discouraged. "When it comes to hair loss, I can't stress enough how important it is to go see a board-certified dermatologist," says Bhanusali. "We now have so many new options and it's much easier to create a comprehensive plan for early hair loss than later in the game."