MSA has a question about hair loss...Why do we lose 100 hairs a day and is it true that eyelashes have a lifespan of 150 days?
The Right Brain responds:
The answer to both questions lies in understanding the cycles of hair growth.
Hair goes through three different stages as it grows: Anagen, Catagen and Telogen phases. The Anagen phase is the active growth phase. This stage can last a up to 4 to 6 years for scalp hair and can produce scalp hairs that are three feet or longer. The Catagen stage follows the Anagen stage. This is basically a transitional stage which means the follicle is slowing down production of the hair. Not much happens here. The third stage is the Telogen, or resting, stage. The hair stops growing and just sits there in the follicle. When the cycle starts all over again with Anagen phase, the old hair is pushed out by the new hair.
The follicles all run on different cycles so at any given time some percentage of your hair is in some stage of each one of these three phases. That’s why on any given day you can lose up to about 100 hairs – because about 100 of the follicles are in a late telogen phase where they are shedding the fiber.
Because this hair growth/shedding cycle is hardwired into your biology there’s nothing you can do about it. The best you can do is take care of the hair while it’s still on your scalp to prevent it from breaking off prematurely. Remember, unlike skin cells, hair does not regenerate its surface once it has grown out. That means any damage you do to hair builds up over time. Every time you wash your hair it causes the hair shaft to swell and contract a little bit this process can cause the cuticles to crack, leaving your hair susceptible to even greater damage. So, while it sounds obvious, the best things you can do for your hair are to limit exposure to washing/drying/combing damage and to use a good conditioner to lubricate the hair.
There are two different types of hairs: Terminal and Vellus. Terminal hairs, like scalp hairs, are thicker and have a longer growing cycle. These are the hairs you have to cut because they get too long. Vellus hairs are short hairs (a millimeter or less), they are very fine, and they have a very short life cycle. Eyelashes are vellus hairs and have a active growing period of only about a month. They then spend several weeks in catagen/telegen phases, so your estimate of 150 days for they lifecycle of an eyelash sounds about right.