Anagen phase - Anagen hair follicle growth

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What is anagen?
Anagen phase is the active stage of hair follicle growth.

During anagen, there is vigorous mitotic activity in the germinal matrix of the follicle and the hair shaft is formed. Addition of new cells and pigmentation takes place at the base of the hair shaft. The anagen period extends from termination of the telogen to beginning of the catagen. The hair shaft keeps growing long till the termination of this phase by some unknown biological or chemical signals.

Anagen phase may last anywhere between 2-7 years and it is considered that the length of the period is predetermined genetically. People of Asian origin are found to have long follicle growth phase and have long strands, sometimes even reaching up to one meter. At any one time, approximately 80-90% of all follicles in a healthy individual are in the anagen growth phase. Different body regions have different anagen periods. The growth period may be short and last up to one or two months in case of follicles on the arms, legs, eyelashes and eyebrows.

It is estimated that on the entire surface of the human body, there are about 5 million hair strands.

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Approximately 50 to 100 of them are shed daily by a healthy individual. Not having long hair of desired length and its regression and balding are distressing concerns. Can we stimulate or prolong the anagen phase? The possibilities are discussed at the end of this post.

Anagen phases

Anagen phase comprises of follicular regeneration and active generation of pigmented hair shaft. Considering the cytohistological aspects, this period is further divided into six sub-phases.

Anagen subphase-I
Before this substage, follicles are in a mode of mitotic and transcriptional inactivity. In subphase-I, transcriptional activation of dermal papilla as well as the secondary hair germ occurs. The dermal papilla increases in size and there is proliferation of epithelial cells of secondary hair germ and their growth.

Anagen subphase-II
The bulb matrix cells, with the advent of vigorous mitotic activity grow down and envelop the dermal papilla. Dermal papilla differentiates into components of hair shaft and inner root sheath.

Anagen subphase-III

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There is continued proliferation and growth of bulb matrix cells and the precursors of follicular components are formed. The follicle reaches its maximum size and the bulb is fully formed. There is proliferation of follicle melanocytes and melanin granules are produced for incorporation of pigment into the hair shaft. The internal sheath attains a conical shape and the papillary cavity of the follicle is constricted at its base.

Anagen subphase-IV
In this phase, the melanin pigment is incorporated into the growing shaft, still within the cone of the internal root sheath. It now reaches the level of sebaceous glands.

Anagen subphase-V
The bulb and follicle reach their final shape and the shaft emerges from the inner root sheath to be in level with epidermis. The telogen shaft is dislodged and shed in this phase.

Anagen subphase-VI
The hair shaft emerges from the cone of external root sheath and transcends the skin surface. The fully formed anagen follicle keeps producing the strand till the activity is switched off.

Stimulating and prolonging the anagen phase

There are some compounds and hormones that can stimulate and prolong the anagen phase.

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Methylsulfonylmethane, a supplement intended for joint pain, is found to lengthen anagen phase of follicle growth which helps to grow long hair. Melatonin (N-acetyl-5- methoxytryptamine) is a hormone produced by the pineal gland which controls sleep regulation, circadian rhythms and follicle growth among many other functions. Application of topical melatonin induces and prolongs the anagen phase.

There are also hormones like androgens, regulating or restricting the follicle growth. Autoimmune and inflammatory factors can target and regress the follicles as in the case of many types of alopecia. Androgen inhibitors, anti inflammatory agents, antioxidants and immunosuppressants are prescribed to deal with the above problems. Hwang et al reported in the International Journal of Molecular Medicine that "adenosine promoted the expression of several growth factors that are responsible for hair growth, including fibroblast growth factors (FGF)-7, FGF-2, insulin-like growth factor (IGF)-1, and vascular endothelial growth factor (VEGF)."

However it advised to consult a physician or a trichologist for treating the follicle problems and rejuvenating anagen phase.

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Reference: 1.Hwang, Hwang, Lee, Kim, Roh, Lee, Kim, Lee, and Kyung-Chul Choi. "Adenosine stimulates growth of dermal papilla and lengthens the anagen phase by increasing the cysteine level via fibroblast growth factors 2 and 7 in an organ culture of mouse vibrissae hair follicles." International Journal of Molecular Medicine International Journal of Molecular Medicine 29 no. 2 (2012): 195-201. 2.Rachita P Dhurat. Deepal J Deshpan. Anagen Hair Syndrome. Int J Trichology. 2010; Jul-Dec; 2(2): 96–100.

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