https://www.youtube.com/watch?v=QPS0wDqivvo
You can watch this video for a better audiovisual understanding of the hair growth cycle.
Introduction:
About the hair growth cycle?Each hair shaft that grows is produced by a complex unique structure called the hair follicle. An average human head of hair contains 1,00,000-1,50,000 hair follicles distributed over the scalp skin. Each hair follicle does not keep continuously keep growing through the life span on an individual; rather each follicle goes through cycles of growing & shedding. This is quite analogous to how leaves on trees often go through shedding & growing through autumn & spring cyclically.
The stages of the hair growth cycle
The hair growth cycle is traditionally recognised as hair follicle passing through successive phases of anagen (growth), catagen (involution) and telogen (resting) with an average duration of 3 years, 3 weeks and 3 months, respectively. Exogen is a side phase that refers to the active release of the hair club fibre. Kenogen refers to the duration between the exogen release and initiation on new anagen cycle.
Anagen Phase (Growth Phase)
This is the active growth phase during which the cells at the base of the hair in the dermal papillae undergo active multiplication and grow upward leading to the formation of the hair shaft. The anagen phase can last from two to five years for the follicles on the scalp. At a given time 85-90% of the follicles are in the anagen phase. The duration of anagen phase is genetically predetermined and varies in different individuals as per their race, ethinicity, age, illness and several other factors. Even in same individual it varies at different sites of the body. Hence a person’s eyebrow (70 days anagen phase) or eyelashes(100-150 days anagen phase) or body hair (6 weeks to 6 months anagen phase) never grow as long as the scalp hair.
Catagen Phase (Involution Phase)
This is the transition phase of the follicle between the anagen phase and telogen phase. During this phase the follicle undergoes involution and cell activity stops with separation of dermal papilla from the hair bulb. There is cessation of the protein and pigment production which are required for formation of hair shaft. Because of the short duration of this phase around 1 to 2% of the hair follicles are in this phase at a given time.
Telogen Phase (Resting Phase)
During this phase the hair follicle enters the a dormant state and remains in this state for one to four months. At a given time on a person’s scalp 10-15% hair follicles remain in this phase. During this time the hair bulb is softly anchored within the skin tissue.
Exogen Phase (Shedding Phase)
During this phase the weak fibrous support holding the bulb in the skin is broken down and the hair strands falls off from the skin.
Kenogen Phase (Interval Phase)
This phase refers to the duration during which the hair follicle remains empty. It reflects the interval after the hair has been shed and until the new growth cycle is still not initiated. Prolongation of kenogen phase is seen in men and women with androgenetic alopecia.
Hair growth and factors it is dependent upon -
Dermal papilla is the powerhouse of the hair root. Its size and production potential dictates the size of anagen hair bulb which further influences the width of hair shaft and the speed of hair growth. The activity of dermal papilla along with the dynamics of the hair cycle are influenced by a variety of factors. Somatomedin C (IGF-1) which is secreted by dermal papilla has anabolic effects on the bulb, apoptosis preventing properties and also linked with induction of platelet-derived growth factor A & B. Apart from being a productive source of hair shaft, the hair follicle can also synthesize or metabolize various hormones, neurotranmistters, neuropeptides and growth factors. The hair cycle clock is an intricate sensitive mechanism which can be influenced by a variety of extrinsic (from outside the hair foliclle) and intrinsic signals(from inside the hair foliclle). The androgen hormones lead to miniaturisation of hair by inhibiting the growth in the frontal temporal region by transforming growth factor beta stimulation. 17 beta estradiol(E2) stimulates elongation of the hair shaft and that is why during pregnancy the hair volume and the hair length improves. Various studies have shown that stress leads to release of stress mediators like substance P, cortisol ACTH and prolactin which can inhibit hair growth. Inadequate nutrition, mental stress, secondary illness, etc. can influence religious trust mediators which can hamper hair growth and negatively influence the hair cycle clock.
How can you boost hair growth ?
A proper assessment and the right approach is key to proper diagnosis and correct treatment. If a patient is experiencing problems with hair fall or hair loss it is imperative to seek an opinion from a qualified certified dermatologist who are the right specialist for dealing with these issues.