Male pattern baldness has been established as an androgen-mediated miniaturization of genetically susceptible hair follicles. In women, male pattern baldness is presumed to occur due to the same process.
Male hormone testosterone is converted to dihydrotestosterone by the enzyme 5-alpha reductase. This enzyme in addition to other places in body is also present in the skin and the root of hair belonging to the susceptible areas of scalp like the fronto-temporal region. This dihydrotestosterone then acts on genetically susceptible hair follicles to cause their miniaturization and eventually leading to death of these hair follicles.
Donor versus recipient dominance refers to the ability of donor hair follicles taken from the occipital area to grow and survive after transplantation to the frontal recipient site. This phenomenon can be explained by the presence of 5-alpha reductase in the cells of the fronto-temporal hair follicles. The hair follicles from the occipital region have less or no enzyme and thus are not influenced by hormonal factors. Further the mesenchyma derived dermal papilla at the base of the mainly epithelial hair follicle controls the type of hair growth. This is also probably the site through which androgens act on follicle cells by altering the regulatory paracrine factors.
Recipient dominant conditions refer to the effect of a diseased recipient area which destroys the healthy donor follicle when transplanted. Few conditions make the recipient area unsuitable for hair transplantation because of various inhibitory factors secreted locally. These conditions include cicatricial (scarring) alopecia, such as discoid lupus erythematosus, lichen planopilaris (lichen planus of skin and hair follicles), and other active scarring skin diseases of hair and scalp. These diseases have to be first treated medically and only upon cure of the primary pathology healthy hair grafts can be transplanted into these areas.