This shampoo is for people with natural, untreated hair who are noticing light thinning — it's not formulated for chemically treated, permed, relaxed, or color-treated hair, which Nioxin addresses with its other numbered systems (e.g., System 2 for treated hair with progressed thinning).

It's a retail, at-home product suitable for any experience level, and works best as part of the full 3-step System 1 routine (shampoo, conditioner, scalp treatment) rather than used on its own.

Nioxin System 1 is built around a specific mechanism: clearing the scalp of sebum buildup that can sit on follicles and make hair look and feel thinner over time, rather than just cleaning hair the way a general shampoo does. It's differentiated by being matched to a specific hair condition — natural, untreated hair with early thinning — so its formulation and the brand's reported results apply to that group specifically, not to hair that's been colored or chemically processed.

• Wet hair and scalp thoroughly.
• Apply shampoo and massage gently into the scalp.
• Rinse thoroughly.
• For best results, follow with Nioxin System 1 Conditioner and the System 1 Scalp & Hair Treatment, using the full system at least 3 times a week.

Pros

• Formulated for a specific, well-defined use case (natural/untreated hair, light thinning) rather than as a general shampoo
• Backed by Nioxin's own consumer-study figures (85% thickening effect, 80% density/fullness increase) for the full system used consistently
• Salicylic acid content helps clear scalp buildup that can interfere with hair growth appearance
• Straightforward daily-use shampoo, no mixing or special technique required

Cons

• Contains sulfates (sodium laureth/lauryl sulfate), which can be more drying for some scalps with regular use
• Contains synthetic dyes (Yellow 5, Blue 1) and methylparaben, which some shoppers specifically try to avoid
• Not appropriate for chemically treated or color-treated hair — using System 1 on the wrong hair type won't deliver Nioxin's stated results
• Reported results are tied to consistent use of the full 3-step system at least 3x/week, not this shampoo in isolation