Hair can be divided in three sections:

  • the stem, which is the visible part of the hair;
  • the root, which is not visible and is located under the scalp. Here the hair cells undergo the process of keratinisation (hardening) that leads to the formation of the stem;
  • the bulb, which is the deepest part of the hair containing its matrix cells able to originate all its structures. It also contains dermal tissue rich in blood vessels, that is the dermal papilla, which provides nutrients for the growing hair.

Hair stem is made up of three concentric cylindrical layers:

  • the medulla is the most internal part and is the core of the hair;
  • the cortex is the middle area that contains melanin pigments responsible for hair colour;
  • the cuticle is the superficial part of the hair and is formed by cells put one of the top of the other like fish scales. They are responsible for protection and appearance of the hair.