The Nioxin’s System 5 Leave-In Scalp & Hair Treatment for Chemically Treated Hair with Light Thinning, refresh the scalp and increase your hair volume. This volumizing leave-on treatment helps to provide thicker-looking hair by increasing the fullness of each hair strand. Nioxin’s Scalp & Hair Treatment is the final step of the 3-part System, which amplifies hair texture while protecting against breakage.