The Nioxin System 6 Step 3 Scalp & Hair Treatment for Chemically Treated Hair with Progressed Thinning is a diameter increasing leave on treatment that thickens hair. Using the Transactive Delivery System 2.0 which thickens hair. For optimal results use with System 6 Cleanser Shampoo and Scalp Therapy Revitalizing Conditioner. Shake the bottle well and then apply evenly to the entire scalp. Do not rinse.