Each hair follicle is independent and goes through the growth cycle at different times .  Most people think of their hair as a giant collective acting in unison. This is not the case.   If it was, it would be a disaster from an appearance point of view.   This will become self-evident as you read on.  The growth phase or active phase known as ANAGEN .  This phase  is when the cells in the root of your hair are most rapidly dividing so more new hair is formed.  During the Anagen Phase, your hair grows around half an inch a month.   It grows  faster in the summer than in winter.  This phase in the life of a hair lasts an average of 3-5 years.   In its full life a hair can average 18-30 inches — so a full-length hair growth averaging 18 to 30 inches. This phase  is generally longer in people of Asian descent, and can last as much as 7 years with hair growing  up to 3 feet long. 

The next phase is a short transitional phase known as the CATAGEN phase.  In this phase signals are sent in and around the follicle to cut individual hairs off from the blood supply and from the cells that produce new hair.   Approximately 3% of all hairs are in this stage at any given time.  This short transitional stage lasts approximately 10 days.  

The third stage of your natural hair growth cycle is the TELOGEN phase, a resting period when strands remain in their follicles but are not actively growing. An estimate of 10-15% of your hairs are in the Telogen phase at any given moment. This stage averages 3-90 days

Finally we get the EXOGEN phase.  As the name implies, this is the goodbye or exit stage.  Individual hair strands are released from their follicles and fall out.  As sad as this sounds it really isn’t.   Now a brand new hair starts .  The whole process begins again.   Back to the ANAGEN stage and the whole life cycle begins again.   As mentioned earlier could you imagine if every hair was not unique and went through the cycle at the exact same time ?  Each hair follicle is independent and goes through the growth cycle at different times.  Otherwise all your hair would fall out at once!  Instead, you only shed a certain number of hairs a day – 80 to 100 hairs on a healthy head of hair.