The Nioxin’s System 4 Leave-In Scalp & Hair Treatment for Color treated with Progressed Thinning, refresh the scalp and increase your hair volume. This volumizing leave-on treatment foam 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.