When I teach doctors about hair loss, I often begin by telling them that hair loss from the scalp is a normal phenomenon. From the time a hair follicle first surfaces above the scalp, it is programmed to eventually be lost or "shed" from the scalp. All hair follicles come programmed with an exit strategy. In fact, hair follicles have a meticulously regulated mechanism for every aspect of their growth.
All hair follicles proceed through four phases as they grow. These phases are called anagen phase, catagen phase, telogen phase and exogen phase. Hairs on the scalp spend about 2-6 years in the anagen phase, 3-5 weeks in catagen phase and 3 months in telogen phase. At the end of telogen phase, hair follicles are shed in the exogen phase. As these follicles fall out of the scalp and a new hair follicle pushes up from below. All hair follicles come programmed with an exit strategy. It’s called exogen. This is why hair loss is a normal phenomenon.
If you reach up an grab a strand of hair on your scalp, it's likely in the anagen phase. In fact, 90 % of hairs on the scalp are in anagen phase. Less than 1 % of hairs are in catagen phase. 10 % are in telogen phase.
Every day about 100 hairs on the scalp find themselves in the exogen phase and are shed from the scalp. This is an important statistic to remember: the normal rate of daily shedding is about 100 hairs. Loss of more than 100 hairs per day is abnormal and indicates excessive shedding. A comprehensive evaluation will usually reveal the cause of a patient's excess shedding.
Dr. Jeff Donovan is a Canadian and US board certified dermatologist specializing exclusively in hair loss. To schedule a consultation, please call the Vancouver office at 604.283.9299