Alopecia
1. Time(aging)
Even though we can see some teen alopecia recently in very rare case, alopecia is occurred from 20’s at least and mostly 30’s in general. A boy who has a bald father has much enough hair.
2. Androgen
Alopecia is occurred by testosterone, the major androgen hormone among men and women. There is a say that in ancient time Aristotle found that masculine feature could become a cause of hair loss. There is rare case of baldness in the people who become eunuch in their childhood. In 1950’s James Hamilton defined androgen is a major cause of alopecia in the basis of modern medicine. So male pattern androgenetic alopecia (MPAGA) and Female pattern androgenetic alopecia (FPAGA) is defined.
3. Gene
No all-aged people have baldness. The progression of hair loss is all different in each people. It is regarded that time and androgen is the main factor for gene expression of alopecia. In the meanwhile, gene is expressed by complicated mechanism and many different factors. So no all-twin boys who have alopecia parents get the same symptom in the future.
Alopecia areata (AA) has different cause. The main cause of AA is regarded as autoimmune disorder.
Physical and emotional stress is also regarded as causes of alopecia.
For females, hair loss is occurred by the events of hormone changes such as Postpartum telogen effluvium, menopause.
Anagen → Catagen transition
1. Cellular self-destruction in the dermal papilla and the root sheath of hair.
① After testosterone is converted to DHT by 5αR enzymes, and then combined with androgen receptors, a transcription is made in the DNA of the cell nucleus.
② Genetic information of DNA is transferred to the mRNA, producing Cell apoptotic cytokines (BMP, DKK-1, TGF-β, FGF5, TNF-α, IL-1, etc.) in the cell and releasing it into the external fluid.
③ The action of β-Catenin, the parent field signal transcription, is inhibited by DKK (Dickkopf)-1 etc. and protein synthesis is stopped.
④ Interruption of cellular activity by BMP2, 4 and apoptosis by Cell apoptotic cytokines such as TGF-β2, TGF-β1.
2. The proliferation of hair cells stops.
3. As the cell differentiation slows down, hair growth stops and becomes the Catagen.
Catagen stage
1. The stage of hair regression (2-3 weeks)
2. Stimulation of cell proliferation due to cytokine action leading to apoptosis
3. The roots of hair move up and the dermal papilla is separated from the hair bulb.
Catagen → Telogen transition
1. The regression of the hair cell stops and the cell activity of the follicle stops.
2. The hair follicle is deformed into a club shape, and the dermal papilla is located near the stem cell.
Telogen stage
1. No hair differentiation, multiplication, regressions, etc.
2. The stage in which the hair gets rest for about three months until the existing hair is completely replaced by the hair of the return to Anagen.
Telogen → Anagen period transition
1. Stem cell activation
① The cytokine Noggin acts on stem cells in the bulge region to regulate BMP and differentiate stem cells.
② Stem cells divide into precursor cells and move to the hair bulb to promote differentiation and proliferation of follicle cells into each region of the follicle.
2. The proliferation of the cells around the dermal papilla occurs.
③ Growth stimulating cytokines such as bFGF, KGF, and FGF9 are secreted from the dermal papilla and surrounding cells, and cytokines such as IGF-1 and VEGF are introduced into the surrounding extracellular fluid.
④ The cell growth signal Wnt overpowered the cell necrosis signal DKK-1 to activate the Wnt/β-Catenin signal, thus promoting synthesis of the proteins needed for the hair growth, and cell proliferation and hair growth start.
3. Formation of new hair
⑤ Factors affecting cell necrosis such as TGF-β2 and β1 are decreased, and factors promoting cell growth such as SOD and growth factors are increased, and then dermal papilla, germinal matrix, internal and external root sheath, connective tissue roots, and hair blood vessels all normalize and new hair grows.
Anagen stage
1. The stage of Anagen (5-6 years)
2. Continuous differentiation of stem cells and production of growth stimulating cytokines.
3. The proliferative action that has occurred in dermal papilla cells.
4. The growth of hair due to continuous differentiation and multiplication of germinal matrix cells and internal and external root sheath.
5. The length of the hair shaft is determined by the duration of the Anagen.