There are three main stages of hair growth, which are:
Anagen: This is the active growth phase of hair follicles, which lasts from 2 to 7 years, depending on genetics and other factors. During this stage, the hair grows continuously and the follicle is anchored deep in the skin.
Catagen: This is the transitional phase of hair growth, which lasts for 2 to 3 weeks. During this stage, the hair follicle shrinks and the hair stops growing, while the hair shaft is pushed up towards the skin surface.
Telogen: This is the resting phase of hair growth, which lasts for about 3 to 4 months. During this stage, the hair follicle is at rest and the hair shaft is released from the follicle, eventually falling out.
After the telogen phase, the hair follicle re-enters the anagen phase and a new hair begins to grow, starting the hair growth cycle over again. It's important to note that not all hair follicles are in the same stage at the same time, which is why we don't lose all of our hair at once.