The Hair Growth Cycle
We are born with all our hair follicles already in place. While some may change in size over time, we don't develop any new ones after birth. As adults, we have about 100,000 individual strands of hair. It's completely normal to lose some 40 to 100 strands every day. Normal hair loss is the result of the growth cycle of the follicles, similar to an 'on off' system. This means that when an old hair 'dies', the growing phase starts again for a new hair to replace it. The hair growth cycle has three different phases:
1. Anagen The Anagen phase is the growing phase or the 'on' phase, which lasts for an average of approximately 1,000 days in the human scalp, but can range from 2 - 6 years. During the Anagen phase, hair cells proliferate rapidly. The hair shaft grows in diameter and the hair reaches maximum length.
2. Catagen The Catagen phase lasts only 1 - 2 weeks - it's the transitional or regressive phase before the resting phase begins. It's essentially when the hair stops growing.
3. Telogen
The Telogen phase is the final resting stage or 'off' phase, which lasts for about 5 - 6 weeks.
When the old hair is in the Telogen phase, activity in the hair follicle is renewed. A new hair in the Anagen phase develops and forces the old Telogen hair out. This is when hairs are lost and you might notice them in the bath or in your brush or comb.
As mentioned in our hair facts section, on average 40-100 hairs are lost due to this natural growth process every day. This is normal hair loss and accounts for the hair loss seen every day in the shower and with hair combing. In healthy follicles these hairs will soon be replaced by new hair.
A variety of factors can alter the normal hair growth cycle and cause temporary or permanent hair loss including medication, radiation, chemotherapy, exposure to chemicals, hormonal and nutritional factors, thyroid disease, generalised or local skin disease, and stress.
You can read more about the causes of hair loss in our types of hair loss section.