Hairs Falling Out in the Shower, and How It Relates to Growth Cycles

how do the hairs that come out in the shower relate to hair growth cycles?

As stated here before, it is normal to lose about 100 hairs a day. To clarify that more, as hair falls out there are hairs that are also starting to grow. Hair grows in cycles and you may notice more hair falling out some days. Hair follicle cells have three phases of growth:

1. Growth phase (Anagen phase) which lasts anywhere from 2 to 6 years. This is the phase where your hair is actively growing at approximately 10cm per year. 85% of hair is at this phase at any given time.
2. Transitional phase (Catagen phase) which lasts about 2 weeks. This is the phase where the hair follicle shrinks and prepares to enter the resting phase.
3. Resting phase (Telogen phase) which lasts about 1- 6 months. This is the phase where hair does not grow but stays attached to the follicle. Some hairs are shed at this phase, but at the end the hair follicle re-enters the growth phase to start the cycle over again. 10-15% of hairs are at this phase at any given time.

If you think about it, the average person has 100,000 hairs on their head, with 100 hairs falling out each day. So in three years, the total hair population will have been replaced (you can do the math for yourself).