Some people use castor oil for hair growth, but evidence is limited. Castor oil contains ricinoleic acid, which may reduce scalp inflammation.

With these Wirecutter-approved picks under $100, you don’t have to spend a lot to get a good deal this Amazon Prime Day.

These are the best hair growth oils and serums for everything from fine hair to coarse hair to thinning and balding.

Update, July 11, 2025: We checked all product prices and availability. Our picks for the best hair growth products remain ...