The outermost, exposed edges are open to the tip of the hair. The cuticle layer is colourless and therefore permits the light to shine through. It makes up a good 10 percent of the hair’s diameter.
The cuticle layer is important for the shine and elasticity of the hair. In young hair near the scalp, the edges of the cells lie flat on one another. The hair is only slightly porous and feels soft and supple. The surface reflects the light giving the hair its shine. The older a piece of hair is, the more physical and chemical stress it has been through. The edges of the cells open along the length and at the tips of the hair, or they are worn away. The hair becomes porous and feels straw-like and rough. It loses its gloss because the uneven surface no longer reflects the light evenly.