Split hair. Coloured scanning electron micrograph (SEM) of a split human head hair. Here, the hair has split midway along the shaft, rather than at the end. Hair is made up of a fibrous protein (keratin). It consists of three layers: an outer layer or cuticle, scaly in normal hair but lost in this damaged specimen; a cortex (visible) containing hair colour pigments; an inner medulla or core (not seen). Hair may split due to excessive shampooing, bleaching, combing, or blow- drying. Occasionally, brittle hair can be a sign of severe vitamin or mineral deficiency. Magnification: x160 at 6x4.5cm size.