Kerastase has discovered what causes persistent damage: CALCIUM!
Damaged hair is porous and absorbs three times more calcium from water than healthy hair, resulting in excess calcium. Each contact with water creates an accumulation of calcium, which leads to persistent damage. Calcium slips between the chains of keratin, breaks their bonds and makes the hair rigid and brittle. Calcium accumulates on the hair's surface, on its scales, making hair rough and dull.