...Regardless of age, balding scalps have a reduced density of terminal hair follicles when compared with non-bald people of the same age. Those aged 30-90 years with normal hair have been reported to have 459 follicles per cm^2, compared with 306 in male pattern hair loss. (30) Recent data suggest that follicular counts in normal adults average 326 per cm^2, and, in Androgenetic Alopecia, 278 per cm^2. (5)
(5) Whiting DA. Diagnostic and predictive value of horizontal sections of scalp biopsy specimens in male androgenetic alopecia. J Am Acad Dermatol 1993; 28: 755-763.
(30) Giacometti L. The anatomy of the human scalp. In: Montagna W, ed. Advances in Biology of the Skin, Vol. 6. Oxford: Pergamon, 1965: 97-120.