Coconut oil is the only one of these three oils with real clinical evidence—it can help with brittle hair and head lice. Castor oil might make hair slightly shinier, but there's weak proof. Argan oil? No solid evidence that it actually does anything for your hair.

Dermatologists reviewed 22 published studies on coconut, castor, and argan oils to see which claims about hair growth, quality, and scalp health actually held up under clinical testing.

Funding not disclosed in abstract