NIOXIN System 4 Scalp & Hair Thickening Treatment, 3.4 fl oz — Leave-In Serum for Color-Treated Hair

Nioxin System 4 Scalp + Hair Thickening Treatment is a leave-in serum designed to nourish the scalp and visibly increase hair diameter and fullness in color-treated, damaged hair with progressed thinning.

This lightweight, 3.4 fl oz treatment works as the finishing step in Nioxin’s three-part System 4 regimen. Formulated to deliver antioxidants, botanicals, and targeted nutrients to the scalp, it helps refresh the scalp environment while improving the feel and structure of weakened, color-treated hair. The formula uses Nioxin’s Scalp Access Delivery System 2.0 technology to help protect strands from breakage and to support a healthier-looking scalp and hair appearance.

How does this treatment help hair that has been color-treated and thinned?

The serum is engineered for hair that has been chemically processed and is showing signs of progressive thinning. It focuses on strengthening the hair shaft and reducing mechanical breakage so individual strands appear thicker. Rather than adding heavy buildup, it leaves hair feeling lighter while helping to sustain color vibrancy.

• Formulated specifically for color-treated, damaged hair with progressed thinning.
• Strengthens hair resilience to reduce breakage during styling and brushing.
• Lightweight, leave-in texture avoids weighing down fine or fragile strands.
• Includes UV-protecting ingredients to help guard color from environmental stress.

What results can I expect and how quickly will I notice them?

Consumers often report a perceptible improvement in thickness, density, and fullness within weeks of consistent use; individual results vary. This treatment is intended to amplify hair structure and provide visible thickening when used as directed with the System 4 kit. For best outcomes, follow the complete three-step routine as recommended.

• Visible thicker-looking hair and increased fullness reported by many users.
• Designed to work as the leave-in step after cleansing and conditioning from the System 4 kit.
• Targets scalp impurities that can contribute to an unhealthy growth environment.
• Regular use supports cumulative improvements over time rather than instant permanent change.

How do I use the Scalp + Hair Thickening Treatment in my routine?

Use this leave-in serum as the final step after shampooing and conditioning with Nioxin System 4 products. Apply directly to the scalp and hair, concentrating on areas with noticeable thinning. Massage gently to distribute the formula; do not rinse out. Style as usual.

• Apply daily or as directed to a towel-dried or dry scalp and hair.
• Target thinner zones with focused application for best coverage.
• Leave in—no rinsing—so active ingredients can work throughout the day.
• Pair with System 4 cleanser and conditioner for integrated results.

What key ingredients and science support this treatment?

The formula combines botanical extracts, antioxidants, and Nioxin’s proprietary delivery system to nourish the scalp and strengthen hair fibers. These components help remove impurities, balance sebum, and deliver conditioning agents that protect fragile, color-treated strands from further damage. The approach focuses on improving the scalp environment to support healthier-looking hair density.

• Antioxidants and botanicals to help nourish and protect the scalp and hair.
• Scalp Access Delivery System 2.0 for targeted ingredient placement.
• Ingredients that help manage excess sebum and remove follicle-clogging buildup.
• UV-protecting actives to help preserve color-treated hair.

Who is this for: Nioxin System 4 Scalp + Hair Thickening Treatment is made for people with color-treated, dry or damaged hair experiencing progressed thinning who want a salon-developed leave-in solution to help strengthen strands, refresh the scalp, and improve the visual thickness of hair. It suits anyone seeking a lightweight, daily treatment that integrates into a complete thinning-hair regimen without adding heavy residue.

Ingredients

Aqua, Phenylbenzimidazole Sulfonic Acid, Niacinamide, Benzophenone-4, Caffeine, Polysorbate 20, Sodium Hydroxide, Benzyl Alcohol, Sodium Benzoate, Phenoxyethanol, PEG-12 Dimethicone, Citric Acid, Cocamidopropyl Betaine, Acetamide MEA, Isopropyl C12-15-Pareth-9 Carboxylate, Tetrasodium EDTA, Propylene Glycol, Methyl Nicotinate, Sodium Chloride, Parfum, Polysorbate 60, Polysorbate 80, Mentha Piperita Oil, Mentha Arvensis Leaf Oil, Menthol, PEG-23M, Camellia Sinensis Leaf Extract, Limonene, Cystine Bis-PG-Propyl Silanetriol, Biotin, Lecithin, Tocopheryl Acetate, Foeniculum Vulgare Fruit Extract, Silica, Faex Extract, Acer Saccharum Extract, Citrus Limon Peel Extract, Saccharum Officinarum Extract, Vaccinium Myrtillus Leaf Extract, Citrus Aurantium Dulcis Fruit Extract, Potassium Sorbate