Nioxin System 4 Kit is a complete 3-step hair care regimen formulated for color-treated hair with noticeable or progressed thinning. This professional-strength system includes a Thickening Shampoo, Scalp Therapy Conditioner, and a Leave-On Scalp & Hair Treatment that work together to remove buildup, deliver lightweight moisture, and strengthen thinning hair without stripping color. Designed to support visibly denser, fuller hair, System 4 helps reduce breakage, improve hair texture, and refresh the scalp while preserving the vibrancy of chemically-treated strands. Ideal for daily use, it offers a targeted solution for those experiencing more advanced hair thinning while maintaining color longevity and scalp health.