A shampoo can not change the chemical structure of the hair, so it can’t alter the thickness of your strands. On the other hand, hair thickening shampoos do work! In order to understand this, you need to know that your scalp contains hair follicles; and each hair follicle houses a hair root. From the hair root, the hair shaft grows. The number of hair follicles in the scalp cannot be altered either.   Hair thickening shampoos create an illusion of thickness! They work by giving the illusion that you have thick hair, by making each strand thicker and decreasing the amount of space between two hair strands. Certain shampoos imbue the hair shaft with panthenol and protein which plumps out each strand and proffers volume.