Hair oils can be used in a multitude of ways depending on the formula, weight, and your hair’s specific needs. Hair can be soaked in oil as a deep-conditioning pre-shampoo treatment, or it can be applied to wet hair pre-blowout as a shine-boosting styling treatment. Lightweight formulas can also be used on freshly styled hair to tame frizz and lock in shine. If you’re not using hair oil as a pre-shampoo treatment that you'll be washing out, Aguirre recommends avoiding applying it too close to your roots and scalp—especially if your hair is already on the oilier side.