Nioxin’s System 1 Leave-In Scalp & Hair Treatment for Natural Hair with Light Thinning works to refresh the scalp and increase your hair volume. This volumizing leave-in treatment helps to provide thicker-looking hair by increasing the fullness of each hair strand. Nioxin’s System 1 Scalp & Hair Treatment is the final step of the 3-part System, which amplifies hair texture while protecting against breakage.