The average adult has 100,000 hair follicles on her
scalp. Brunettes have the highest number of scalp follicles
(about 155,000) followed by blondes (140,000) and redheads
hair follicle is divided into three anatomic and functional
2. The isthmus and
3. The lower follicle, which contains the hair bulb.
infundibulum includes the area from the skin
surface to the opening of the sebaceous duct. The isthmus
extends from the sebaceous duct to the insertion of
the arrector pili muscle and is the site of the hair
bulge. The lower follicle includes the deepest straight
portion of the hair follicle and the hair bulb. The
hair bulb is composed of the hair matrix, which in turn
surrounds the follicular papilla.
infundibulum and the isthmus are the permanent
portion of the hair follicle, as they do not undergo
any structural changes during the hair growth cycle.
The lower follicle segment, in contrast, is the transient
portion of the hair follicle.