A normal human scalp contains about a 100,000 to 150,000 hair follicles. Now these hairs are not present as single strands, but as 1, 2, 3, 4, multiple hairs together. This collection of hair is termed as follicular unit or the graft.
Normally, about 90% of our hair is in active stages of growth and that active stage of growth is called as the Anagen phase or anagen cycle. Anagen cycle can be between 3 – 7 years, which is an active hair growth. The second hair cycle is the Catagen cycle. In catagen cycle there is no active hair growth but the hair is stagnant, which is for a short period of time for about 2 – 3 weeks.
Third cycle is referred to as telogen cycle. In telogen cycle you will notice hair loss because the hair follicle goes into the resting period. The telogen cycle last for about 3 – 4 months. At any point of time, 10% of hair will be in telogen cycle which will show active hair loss. If you notice 50-60 strands which fall every day, there is nothing to worry about because those strands will be in the telogen cycle. As long as there is no change in the external appearance you don’t need to worry.
In common baldness or androgenetic alopecia is caused due to the successive replacement of normal hair with thinner and finer hair and not because of the excessive hair loss. The process of replacement of normal hair with thinner and finer hair is called as miniaturization. In androgenetic alopecia, the anagen phase of hair cycle period is reduced and therefore you will have more number of anagen cycles or growth cycles in a short period of time.
Thus an anagen cycle last for 3 – 7 years and catagen cycle lasts for 2 – 3 weeks. A telogen cycle last for 3 -4 months. All these 3 cycles constitutes one hair growth cycle.