Hair has a natural cycle that is controlled by signals from the scalp and around the body.
When a hair dies, another one will start to grow almost immediately, from the collection of stem cells at the base.
Between beginning to grow and then falling out, many years later, each individual hair passes through four separate stages of the growth cycle: anagen, catagen, telogen and exogen.
Anagen is the first phase and is commonly known as the ‘growing phase’ of the hair growth cycle. Anagen begins when new hair emerges and grows up through the scalp to push the old hair, out. The process then continues and the hair multiplies and keeps on growing for anything from two to seven years, determining the length of the hair.
Catagen is otherwise known as the ‘transition phase’ and lasts for around 10 days. Hair growth stops during this phase, parts of the follicle become broken down and due to the hair shaft detaching itself from the stem cells (dermal papilla).
Telogen is often referred to as the ‘resting phase’ and can last for between 3 and 6 months. This particular phase of the growth cycle occurs when the hair is no longer attached and is beyond repair; it has lost condition and can look dull. As this phase nears the end, other new hair follicles begin to come to life, as in the Anagen phase. These new follicles develop and push the old, Telogen hair out. Around 10 to 15 percent of hair is involved in this phase, whereas up to 90 percent of hair is continually in the Anagen phase.
Exogen, also known as the ‘shedding phase’, is where the old hair drops from the head.
Roughly 50 to 150 hairs can fall out on a daily basis, and this is considered to be normal.
For many people, their hair growth cycle continues in the same manner for the duration of their lives, while for others, factors such as pregnancy, hormones, diet and medication can cause the process to alter.