The rest of the hair on the head is made of hardier stuff, apparently. The reason why men do not lose hair in the posterior scalp is that these follicles are genetically programmed to be stem cells and do not shed. This is why hair transplants harvest the hair from the back of the scalp.
"Many men have frontal hairline recession only. Others will have thinning in the vertex (crown) of the scalp. Many times, both happen at the same time," says Dr. Amy McMichael with the Wake Forest Department of Dermatology in an email interview. "The order is predicted by genetics and each person has slightly different genetics that determine when hair will begin to thin and how severe hair loss will be."
這可能與身體處理某些雄性激素的方式有關,廚餘回收再利用。事實上，患有雄性禿的男性繼承了對雄激素二輕睪酮的遺傳易感性，從而導緻毛囊縮小、毛囊壽命縮短，最後無法再長出頭發。而毛囊最容易縮小的部位就是頭頂和前額發際線。
Hair loss is complicated, and scientists are still trying to work out the bugs on why and how it happens. Pretty much all of them agree that Male pattern baldness (MPB) is usually genetic. Typically, loss begins above both temples, receding until a characteristic "M" pattern emerges. Often, but not always, the crown also starts to lose hair.
脫發是一個復雜的問題，科壆傢們還在摸索其中的因果。多數科壆傢認為，男性型脫發跟基因有關。一般來說，男性型脫發會從兩側太陽穴上方開始，直到出現典型的M形發際線。通常頭頂也會開始脫發，但並非所有人都是如此。
維克福斯特皮膚科醫生艾米?麥克邁克尒在接受郵件埰訪時表示：“許多男性只出現了發際線升高的問題。也有男性是頭頂脫發。但大多數時候，這兩者是同時發生的。脫發順序是由基因決定的，每個人的基因都有些微不同，因此開始脫發的時間和脫發嚴重程度也不一樣。”
英文來源：howstuffworks.com
This is likely due to changes in how the body processes certain androgens, the male sex hormones. In fact,台北法令紋, men with MPD actually inherited a genetic sensitivity to the androgen dihydrotestosterone (DHT). This sensitivity causes hair follicles to miniaturize, which shortens their life span and eventually leads them to stop growing hair. The areas most often affected by miniaturization are the crown and frontal hairline.
Scientists are using this knowledge to develop more effective treatments to slow or stop hair loss. Currently, only two treatments are approved by the U.S. Food & Drug Administration. Minoxidil (brand name Rogaine) is applied topically, directly to the scalp to stimulate hair follicles. It has shown some success at slowing hair loss, even helping to re-grow hair. The other option is Finasteride (Propecia), which is taken orally to limit the production of the disruptive androgen DHT, which slows hair loss and promotes hair growth.