I have a few posts coming up that deal with the normal hair cycle, and I really need to have something to refer to. So, here it is, a looooong overdue post that just shows the normal hair cycle.
At any given time, each hair follicle is in a different part of the normal cycle of hair growth. Each follicle will cycle through these phases, though they can become "stuck" in a given phase depending on other factors in the body, such as pregnancy. Note that the hair follicles are not synchronized with each other, each follicle cycles on its own and at its own pace.
About 90% of hairs are in Anagen at a time. Typically this phase lasts years, up to 7 years in some people! The rate of growth of a hair follicle on your scalp can be 0.3 mm/day, but other areas of your body will grow much more slowly and their anagen phase can be much shorter. For example, eyebrows typically only stay in Anagen for a few months.
This is when the hair follicle is starting to transform into the "rest" phase. The deep part of the hair follicle will slowly regress, pulling upwards toward the hair shaft and the surface of the skin. This takes a few weeks on your scalp, and about 1-2% of your hair is in catagen at a given time. The hair shaft is kind of sitting there in the hair follicle, no longer growing, so the base of the hair shaft (that dermal papilla) isn't really connected to the hair by the time you enter telogen.
Finally, the hair follicles are ready to rest! The hair follicle releases the hair shaft and it falls out, under normal circumstances you can lose 50-150 hairs/day from your head. Note that the hair can fall out on their own, or in some circumstances (like what is pictured in this image), the new hair as you start Anagen will actually be what pushes out the old hair.
The hair follicle can "rest" for up to 3 months before returning to Anagen phase. About 8-10% of your hair follicles are in telogen phase at a given time.
Everyone's hair has its own cycle of typical time in each phase of growth and its own growth rate. All the follicles on your body will do their own thing, and it changes depending upon where on the body the hair is. I certainly wouldn't want my eyebrows to behave like the hair on my scalp! I hope this helps some, and be on the look out for some upcoming posts that refer to the normal hair growth cycle!
Image: Alila at 123rf.com