The problem of receding hairline in men, also called male pattern baldness, stems from a medical condition known as androgenetic alopecia, which occurs when the hair follicles in a man's scalp thin out and finally stop growing back altogether. The condition generally can be identified by the thinning of hair on a man's head and the subsequent formation of an M-patterned hairline where it remains. It might also recede even further into a horseshoe shape, where the center of the scalp is bare and hair only remains on the back and sides of the head. This type of baldness is common among older men, but age is not the only cause. The other two known reasons for male pattern baldness are genes and hormonal changes.
There is a strong coincidence between age and a receding hairline in men. About 25 percent of men older than age 30 start to lose their hair, and by the age of 60, it rises to more than 60 percent. Age, however, merely elevates the risk of male pattern baldness and determines the time of its onset; in rare cases, it also happens to teenagers. Although age is popularly considered the primary cause of progressive hair loss, it is more of a contributing factor or a catalyst for other underlying factors.
Changes in hormones is one of the underlying causes of a receding hairline in men. At some point in a man's life, his body produces an enzyme called 5-alpha reductase, which binds itself to the male hormone known as an androgen. This interaction results in the production of dihydrotestosterone (DHT), another form of the male sex hormone. DHT partially blocks vitamins and proteins from reaching hair follicles, and as a result, the hair in the affected follicle will not grow as long or as thick as it used to grow. Eventually, the hair follicle starves from lack of nourishment because of a complete blockage, and hair that falls out fails to grow back.
Genetic inheritance is another major factor that affects the onset of hair loss. The gene known as the androgen receptor (AR) gene was the first gene that was specifically identified as the cause of a receding hairline in men. The stronger the AR gene, the earlier and more pronounced the hair loss will be. Originally, the AR gene that is responsible for hair loss was identified as being passed down from mother to son, but more recent studies have shown that it also can be inherited from the father. Further research has identified another gene on the 20th chromosome that can trigger male pattern baldness even for men who do not have a strong AR gene.