Nioxin is a line of herbal based hair products that are sold in salon to treat thinning hair and hair loss, whether due to age, overprocessing, or a genetic predisposition to thinning hair. When you go to the Nioxin website, you fill out a brief quiz about your hair type and hair concerns, and it lists the Nioxin products that are suitable for you. For example, a person with medium to coarse, chemically treated hair whose hair is normal or only starting to think would be advised to use Nioxin's System 7, which is designed to moisturize the hair and scalp and protect them from chemical residue from processing like coloring, perming, or relaxing.

The other Systems, System 1, System 2, System 3, and System 4 through 9
Nioxin Research Laboratories, which is owned by Proctor & Gamble, offers products like its Scalp Renew, which is an anti-aging scalp renewal treatment that is a dermabrasion treatment designed to clear dead cells and open follicle sites, increase cellular turnover on the scalp, increase collagen production, and add density and strength to hair. 
Nioxin's products are based on the theory that the skin on the scalp ages for the same reasons as other skin, and the better the condition of scalp skin, the better the condition of the hair. Follicles that are plugged with oils or buildup of dead skin cells provide a less than optimal environment for the growth of thick, healthy hair. Nioxin Scalp Renew, for example, contains vitamins,  beta hydroxy acids, and enzyme exfoliants that are designed to restore scalp vitality and add strength, shine, and density to hair. The suggested price for having Nioxin's in-salon scalp treatment is around $60, but prices are set by individual salons.

Up to 15% of hairs on the scalp are in their "resting" phase at any time. Because the hair isn't actively growing, it may become trapped in follicles due to scalp buildup, which Nioxin shampoo is designed to treat. A normal, healthy scalp can lose up to 100 hairs a day. The Nioxin products are also designed to reduce static electricity in the hair, which gives it a "flyaway" appearance by entering the cortex of the hair and adding moisture and strength. The Nioxin products called "Bliss" and "Glossing Color Shield" add thermal protection, which helps reduce damage from blow drying and use of heated hair tools like straightening irons and curling irons.

While Nioxin products do not stop the conversion of testosterone to DHT (a leading cause of thinning hair - particularly in men), daily use of Nioxin products cleans away excess sebum that contains DHT, getting DHT off the scalp.
Nioxin reports that 9 out of 10 people who regularly use Systems 1 through 8 as directed can notice increased hair density, better hair moisturizing, and a thickening effect. People with fine hair or thin looking hair notice a thickening effect after 10 applications.