This shampoo is for people with color-treated hair who are dealing with progressed (more noticeable) thinning — Nioxin's System 4 specifically targets that combination, rather than color-treated hair with only light thinning (System 3) or natural, non-colored hair (Systems 1/2). It's intended for daily use as the cleansing step in a three-part regimen, suited to both men and women, and works in either a professional salon setting or as an at-home routine, for anyone who wants a scalp-focused cleanse that's still labeled safe for color-treated hair.

The reason to reach for this rather than a standard color-safe shampoo is that it's trying to solve two things that usually pull in opposite directions — a scalp that needs real buildup removal (via salicylic acid and cleansing surfactants) and colored hair that needs its color protected. Most shampoos pick one side of that trade-off; System 4 is formulated to cleanse the scalp thoroughly for someone with more advanced thinning while still being labeled safe for chemically treated color, which is the specific niche it's built to fill within Nioxin's broader system.

Massage the shampoo into wet hair and scalp, work it into a lather for about a minute, then rinse thoroughly. It's intended for daily use, paired with the System 4 Scalp Therapy Conditioner and the System 4 Scalp & Hair Treatment as part of the complete regimen.

Pros: genuinely dual-purpose — it's built to give a real scalp cleanse (salicylic acid, sulfate-type surfactants) while still being labeled color-safe, which is a harder balance than a shampoo made for just one of those needs; it's positioned within a coordinated three-step system rather than sold as a stand-alone cure-all. Cons: because it's a sulfate-based, deep-cleansing formula, it's a more assertive shampoo than a gentle, moisture-first color-care shampoo, so it may not suit someone with very dry or fragile color-treated hair outside the System 4 context; it's specifically for progressed thinning paired with color treatment, so it's the wrong match for lighter thinning or non-colored hair.