Hair oil is an oil-based cosmetic product intended to improve the condition of hair. Various types of oils may be included in hair oil products. These often purport to aid with hair growth, dryness, or damage.When applied to wet hair, it locks in moisture and works much like an intensive treatment to provide deep nourishment and hydration. Hair oil is often applied to dry hair as the last step in your styling routine to add moisture, prevent frizz, amp up the shine, and prevent breakage.