Review: Life Cycle of a Hair Follicle

00:01 Next up, we're gonna talk about alopecia, or colloquially known as "hair loss" First off, before we start talking about the different things that can cause hair loss, we should discuss the life cycle of a hair follicle which is depicted here in the schematic.

00:16 This is basically a hair follicle from womb to tomb, starting with the Anagen phase.

00:21 Seen here in this little block of scalp is a hair bulb, the hair follicle itslef and then a derma papillae which it's attached to, which is the growing zone for hair follicle.

00:32 So the anagen phase is a period of growth for hair follicle and it essentially dictates how long a hair on a particular area is going to be.

00:39 On the scalp, this phase coul be in the order of many years or even decades.

00:43 Whereas this phase is fairly short on the eyebrows, which is why we don't have to comb our eyebrows.

00:50 The anagen phase then transitions to a Catagen phase, which is a fairly brief phase.

00:54 It ultimately leads to the Telogen phase.

00:57 And all we can see is that the hair follicle is slowly separating from the dermal pappillae and ceasing its growth.

01:04 The telogen phase is a potentially prolonged phase of rest for the hair follicle.

01:09 The hairs may not grow for long periods of time but ultimately will be shed in a phase called exogen - not shown here.

01:17 So everyday about 50-100 telogen phase hair shafts are gonna be shed and replaced by 50-100 brand new anagen phase hair shafts.

01:28 A simple test to try and determine whether or not there's a pathologic amount of hair cells in the telogen phase is called the Hair Pull test.

01:35 As you might imagine, since those hair follicles are fairly uprooted and no longer connected to the dermal papillae, If you tug on certain hair cells, if a large proportion of them are in the telogen phase, you're gonna tug a lot of hairs out all at once.

01:49 Whereas for normal hairs, normal scalp tissue, when you pull on the hairs, only a few - probably less than 3 would come out by pulling on a small grouping of hair follicles.