via NaturallyCurly.com;

Panthenol is a form of Vitamin B5. It is small enough to penetrate through the cuticle of hair and is a highly hygroscopic (water-attracting) chemical, acting as a humectant, attracting water to itself. It soothes irritated skin and helps hair retain moisture in the cortex and on the surface, leaving it more pliable, shinier and slightly thicker.