To understand why hair loss happens, it's important to know about the hair growth cycle, what hair is and how it grows.
Hair is found almost everywhere on the human body. Its forms range from thick, wavy tufts on some scalps to the tiny fair-coloured strands that dot almost every portion of our bodies except the palms of our hands and the soles of our feet. The structure and growth cycle of all human hair is the same.
The portion of our hair visible to the outside world is called the shaft. But the story of hair really begins below the skin, where each hair is contained within a pouch-like tube called the follicle. At the base of the follicle is the root, the oval-shaped centre where hair growth activity begins. And jutting into the bottom portion of the root is the papilla, which contains the vital capillaries linking the body's blood supply to each growing strand of hair.
Hair growth occurs in three different phases.
The Anagen phase is the growing phase or the 'on' phase, which lasts for an average of approximately 1,000 days in the human scalp, but can range from two to six years. During the Anagen phase, scalp hair cells grow rapidly at an average rate of one-half to one inch per month. As hair grows, the cells of the hair move closer to the skin surface, being replaced along the way by new, rapidly reproducing cells below. The hair shaft grows in diameter and the hair reaches its maximum length.
The Catagen phase lasts only one to two weeks. It is the transitional or regressive phase, before the resting phase begins. It is essentially when the hair stops growing.
The Telogen phase is the final resting stage, or "off" phase which lasts for about five or six weeks. When the old hair is in the Telogen phase, activity in the hair follicle is renewed. When the growth process resumes, the hair falls out of the follicle and is replaced by a new, emerging hair.
The most common type of hair loss in adult men is known as Androgenetic Alopecia or Male Pattern Baldness (MPB), which accounts for approximately 95% of all hair loss among males. It's believed to be caused by a combination of three factors:
With male pattern baldness, the hairline begins to recede into an "M" pattern. At the same time or later, hair loss exposes the crown of the head. As the condition progresses, the point of the "M" continues to recede, while the bald spot at the crown widens. Eventually, the thinning crown and receding point may meet. This leaves only a horseshoe-shaped fringe of hair encircling the back and sides of the head.
Individuals genetically predestined to develop male pattern baldness have normal hair follicles in the horseshoe-shaped fringe area of the scalp. But, the hair follicles in the area destined to become bald are genetically predetermined to become sensitive to a normal body compound called Dihydrotestosterone (DHT). DHT is produced from testosterone by an enzyme called 5 alpha-reductase.
Genetically sensitive hair follicles shrink when exposed to DHT. As the follicles become smaller, the hair growing Anagen phase shortens and the resting Catagen and Telogen phases lengthen. The hair becomes increasingly thinner, shorter and less deeply rooted. Eventually, hair growth stops.
While it is still not known exactly why hair loss occurs among certain people, researchers have noted a greater incidence among various racial and ethnic groups. Caucasians, for example, are more likely to lose their hair than Asians. Current evidence suggests that the genetic predisposition can be passed down equally from both the mother and the father's side of the family.