Zenius Hair Serum for Men & Women Zenius Hair serum is a product that is applied to the hair to add shine, reduce frizz, and help protect the hair from damage. It is typically a liquid or lightweight oil that is applied to the hair after washing and drying. Hair serum can be used on all hair types but is especially beneficial for those with dry, damaged, or frizzy hair. It can help to smooth the hair, making it easier to style and manage. Some hair serums may also contain ingredients that can help to nourish and moisturize the hair, helping to improve its overall health and appearance. Hair serums are typically applied to the ends of the hair, but can also be applied to the mid-lengths and roots for added nourishment.