Hair is part of the family of integuments that includes body hair, nails and hair. The visible part is mostly composed of keratin.
Hair consists of the hair shaft, the outer visible part, and the bulb located under the scalp, 3 or 4 mm from the surface. At the base of the bulb is the dermal papilla, the biological motor of hair.
The hair follicle, more commonly known as the “hair root”, is composed of the bulb and epithelial sheaths.
Around the hair shaft is the internal epithelial sheath, which plays an important role in hair growth and the outer epithelial sheath, a stem cell pool involved in the hair cycle.
In the bulb, the division of the keratinocytes is intense and is the source of the hair shaft and epithelial sheaths.
The dermal papilla allows oxygenation and irrigation of the bulb. It consists of fibroblasts that produce the extracellular matrix. Highly vascularized, it ensures the nutrition of the bulb and regulates its biological functions.
The connective tissue produced by fibroblasts is predominantly collagen. It plays an important role in anchoring hair.