Mechanisms of Laser-Induced Hair Regrowth

Male androgenetic alopecia (AGA) is the most frequent type of thinning or loss of hair in males. The condition, also known as male pattern baldness, causes hair loss as early as late adolescence. Polygenic heredity is assumed to be the primary cause, although the male hormone testosterone plays an important role, seemingly independent of genetic predisposition. In the hair follicle cells, testosterone converts into the biologically more active metabolite, 5α-dihydrotestosterone (DHT) catalyzed by the enzyme 5-alpha reductase. This hormone binds to androgenic receptors in the hair follicle and the specific bond triggers cellular processes, which reduce the anagen phase of the hair cycle. For this reason the hair passes earlier into the telogen phase and falls out. Gradually, over succeeding cycles terminal hair converts into thinner and shorter vellus hair (i.e. the retrograde phase of the cycle) and the hair follicle becomes minute. The density of the androgenic receptors in the hair follicles varies according to location and this is genetically determined. Age factors too play an important role in AGA, the first manifestation is usually appearing in the third decade. Further factors are probably involved. In males usually symmetric fronto-parietal retraction of the hair-line occurs. The hair in the central part of the vertex is rarefied and thin, and the skin becomes transparent. The alopecia progresses and sooner or later results in a bald spot on the vertex. The remaining hair is distributed in crown-like pattern above the ears and at the scruff of the neck. However, it also becomes gradually thinner and silky, and growing more slowly. Histological findings of the initial phase are characterized by focal perivascular basophil degeneration of connective tissue around the lower third of the anagen follicle. A perifollicular lymphocyte infiltrate then occurs. In the late stage, involution of all the structures in corium becomes apparent; the terminal hairs turn into subtle, vellus hairs, which are located higher in the dermis. 2. Low-Level Laser (Light) Therapy