The hair on a person’s scalp is constantly engaged in a dynamic process. It is in a constant state of flux that involves the existence of hair strands at different stages at any given time. This is divided into different phases: anagen, catagen, telogen and exogen. These phases make it easier to observe the changes of the hair growth cycle and will provide insight on how each contributes to its overall function.
Hair growth takes up the longest period in this cycle. It can last anywhere between two to eight years depending on the health and age of the person. This is known as the anagen or the growth stage. There are about 85% of hairs on a person’s scalp that is engaged in this stage at any one time. It is the most active period during which the hair cells at the root of the hair follicle divide rapidly to produce hair at the rate of about one centimeter every twenty eight days. There will be a difference in the ability of a person to grow long hair due to the length of activity of this stage. A shorter phase would in turn, produce shorter length hair. Eyebrows, eyelashes and hair on the limbs are evidence of this. It has an active period of only thirty to forty-five days.
The next stage is called catagen or the transition phase. It usually lasts for about ten to twenty days. This is the period where growth gradually stops and the club hair begins to develop. The outer root sheath shrinks and attaches to the root of the hair strand. It then detaches itself from the dermal papilla. There are about three to five percent of hairs in this stage at any given time.
This is followed by the telogen or the resting phase. It lasts for about two to three months and is the period where club hair is fully formed. A hard, whitish and dry substance can be observed at the tip of the hair strand if it is pulled out. Around ten to fifteen percent of hair follicles account for this phase. New hair starts to form during this period with the old hair slowly being pushed out of the roots.
The hair growth cycle is rounded out by the exogen or the new hair phase. This is the period where the old hair is completely shed and new hair starts to appear. About fifty to one hundred fifty hairs are shed every day. This is a normal rate occurring at different areas of the scalp. The end of this phase will be the beginning of the anagen stage that starts a new hair growth cycle.
A person will regularly exhibit these traits throughout their lifetime. They will do so even if they are going through certain hair loss conditions such as androgenic alopecia. The hair follicles that are unaffected by the condition can still go through the cycles. There are however, times when it can be interrupted.
One of the most common circumstances when these hair growth stages are disrupted is the occurrence of telogen effluvium. It is characterised by a rapid shift between the anagen stage and the telogen stage. Clumps of hair can be lost in the process. This can be seen on the pillow after waking up, on the hairbrush or in the shower drain. It is brought about by traumatic experiences such as the loss of a loved one, accidents, major surgery, divorce, childbirth or other stressful experiences. It will manifest itself three months after the event though the hair growth cycle will usually resume its normal functions within six months.