Hair serum is a liquid-based treatment usually formulated using silicones that provide a protective layer over the hair fibre, assisting in smoothing frizz. This smooth layer then reflects the light, which is how serum gives your hair a shiny, not greasy, finish.Detangle your strands before you proceed to style your hair. This will prevent frizz and hair breakage. The serum will form a protective layer over your strands and protect them from damage.