The scalp is divided into five layers, which are the skin, connective subcutaneous tissue, galea aponeurosis, loose connective tissue, and periosteum over the cranium.
The skin contains all the epidermal appendages, including the hair follicles which extend into the underlying connective subcutaneous layer. How deep the hair follicle is also depends on the stage of hair cycle. Just before fall the hair follicle is quiet superficial in the scalp. In areas which have undergone hair loss, there is thinning of the outer two layers. This can be better appreciated on comparing the skin punch biopsy from the scalp in recipient areas with that in donor areas.
Blood supply to the hair follicles come through the vascular channels in the subcutaneous layer. This has importance while harvesting hair from the donor areas where one has to stay superficial along the connective subcutaneous tissue layer to avoid compromising hair density or hair loss at the donor area. One must not try to reach galea during graft harvesting to avoid compromising scalp blood supply and future neuroma formation (sensory innervation of the scalp closely follows the vascular supply). Deeper penetration might on occasions can lead to reduced scalp sensation over few weeks when a large number of graft recipient slits are made along the hairline.