Chapter 2 59 an “M” shaped recession of the frontal hairline and hair thinning over the center of scalp (Figure 7). As the disease progresses, thick terminal hairs on the scalp turn into thin and miniaturized ones which offer poor coverage of the scalp. This may eventually lead to complete baldness of the affected area (Figure 8). Hair loss usually progresses slowly and without noticeable hair shedding, though episodes of acute exacerbation may be encountered occasionally. The severity of hair loss is classified into seven stages according to Hamilton-Norwood classification.75 The pathogenesis of AGA is generally regarded as androgen- dependent with a genetically susceptible background. People with father affected by AGA have higher risk to develop the disease.76 Dihydrotestosterone, a potent androgen, is regarded as the key player in the miniaturization process in AGA. The choices for treatment are limited. Topical minoxidil and oral finasteride are widely used to halt or partially reverse the progression of hair loss but long-term Figure 7 Androgenetic alopecia, Hamilton-Norwood type 3v. (A) Thinning of hair over the mid-scalp and vertex area (B) Recession of the frontal hairline (C) Miniaturized hair follicles over the mid-scalp area (left panel) vs. normal terminal hair follicles over the occipital area (right panel).