The hair follicle is a structure that encases the lower part of the hair shaft. Each follicle contains blood vessels that nurture new hair growth. All hair follicles are present at birth; throughout the lifetime each follicle grows and sheds single hairs in a repetitive cycle.
The growth phase for a single new hair lasts two to three years.
At the end of this time, growth ceases and the follicle enters a resting phase.
After three to four months in the resting phase, the hair is shed and the next growth cycle begins.
On a normal scalp, approximately 80 to 90 percent of follicles are growing at any time. Each day, about 75 follicles shed their hair while the same number enter a new growth phase.
In men with androgenetic alopecia, hormones related to testosterone (also called androgens) cause hair follicles to have a shorter than normal growth phase, resulting in hair shafts that are abnormally short and thin. These follicles are said to be “miniaturized.” The reasons why some men develop androgenetic alopecia and others do not are not fully understood. It is generally accepted that genetic background strongly influences the development of androgenetic alopecia in men, but the exact way in which family history affects a man’s chance of developing hair loss has not been determined .
Genetics also appears to play a role in the risk for androgenetic alopecia in women, although other factors (some of which remain unknown) may also be important . As an example, abnormal levels of androgens in the blood are the cause of androgenetic alopecia in a minority of women . Additional research is necessary to provide a better understanding of the role of genetics and other factors in androgenetic alopecia. -Continue Reading…