While all shampoos are made to clean hair and remove dirt and other particles from the scalp, the shampoos with thickening ingredients create additional space between each strand of hair. Shampoos with protein, the B-vitamin panthenol and keratin all work by plumping up hair strands. Therefore, the hair looks thicker even though the strand count remains the same.
Protein in hair-thickening shampoos works by fortifying the hair shaft, causing the hair to more easily attract moisture. When strands are moisturized, they take on a plumper appearance. Protein also prevents the hair from becoming brittle and weak, which can lead to thinner, less bouncy hair.
Panthenol is part of the B-complex family of vitamins. The substance has been proven to volumize the hair by as much as 10 percent. Like protein, panthenol restores moisture to the strands, which causes the hair to appear thicker overall.
Keratin, which works by locking in moisture in the hair strand, naturally makes up the primary bulk of the hair shaft. Along with collagen, keratin is essential to hair thickness and growth.
The hair shaft itself is defined by three layers: the medulla, cortex and cuticle. The medulla is the innermost layer, while the mid layer is called the cortex. The cortex controls the thickness and strength of the hair. The cuticle, or outside layer, is designed to safeguard the other two layers of hair.