At birth, we have approximately 100,000 hair follicles covering our scalp. It is generally believed that this is the largest number of follicles we will ever have and no “new” hair follicles will develop after birth.
Hair has two separate structures - the follicle in the skin and the shaft we see.
A hair is a flexible keratin thread about 0.1 mm thick, with great strength and elasticity.
Follicle - The hair follicle is located in the dermis. At the base of the hair follicle is the dermal papilla which is fed by the bloodstream that carries nourishment to produce new hair – it is the point from which hair grows. Surrounding dermal papilla is the onion-shaped hair bulb which new hair is being made inside. New cells are continuously produced in the lower part of the bulb. As they grow and develop they steadily push the previously formed cells upwards.
The follicle is surrounded by two sheaths - an inner and outer sheath. These sheaths protect and mold the growing hair shaft. The inner sheath follows the hair shaft and ends below the opening of a sebaceous (oil) gland. The outer sheath continues all the way up to the gland.
The sebaceous gland produces sebum to condition the hair. More sebum is produced after puberty. The sebum production decreases in both men & women as we age, but more so in women.
Shaft - The hair shaft is made up of three layers. The inner layer is called the medulla. The next layer is the cortex and the outer layer is the cuticle. The cortex makes up the majority of the hair shaft and contains fibers which are important for hair‘s strength and elasticity.
The cuticle is formed by tightly packed scales in an overlapping structure similar to roof shingles and serves to protect the cortex. There are pigment cells that are distributed throughout the cortex and medulla giving the hair its characteristic colour.
The outer root sheath surrounds the hair follicle and secures the hair shaft within the follicle.