Hair oils and hair serums have different purposes. Hair oils are heavier and thicker, designed to provide deep hydration, nourishment, and manageability, especially for dry or damaged hair. They are often left in for extended periods or overnight. Hair serums are lightweight and work to add shine, smoothness, and sometimes heat protection. They are ideal for frizz control, adding gloss, and protecting hair from styling damage. Serums are suitable for all hair types and can be used daily as a finishing product.