Keratin is depleted when hair is damaged physically, chemically and/or from environmental factors, such as the sun. This keratin loss exposes the hair’s cortex, making it susceptible to additional damage, and causes porous spots to develop—much like potholes in a road. Replenishing lost keratin helps to correct porosity and smooth the hair’s surface. It restores strength and elasticity, giving the hair a more youthful, healthy appearance.