Hair grows from a follicle within the scalp, where it receives the nourishment it needs to grow. Each hair goes through three distinct phases during its life cycle, so at any given time, you have thousands of hairs passing through each phase.
ANAGEN: Growth Phase
This phase lasts an average of 3-5 years, with hair growing about half an inch per month.
CATAGEN: Regression Phase
A short, transitional phase that lasts about 10 days, when the follicle begins to contract.
TELOGEN: Resting Phase
Strands remain in their follicles, but are not actively growing. After about 3 months, the hair is released and falls out.