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AGA (androgenic alopecia)

What is AGA (androgenic alopecia)?

Its official disease name is premature androgenic alopecia in Japan.
In Western countries, it is called as male pattern baldness because it is a unique hair loss in men or androgenic alopecia (AGA) because it is associated with androgenic hormones.
It is commonly called as androgenic alopecia in Japan and recently has been abbreviated to AGA.


Hair gradually becomes thinner mainly in the rear of the head (O shape) and hair recesses in the front and the sides of head (M shape), which is characteristics of androgenic alopecia. There is a mix type between O shape and M shape. It can begin as young as 17-years of age, but more commonly occurs amongst men in their twenties and thirties. It can also occur in men over 40 years old.
Initially, a large hair follicle*1 enters the resting phase*2 earlier than normal and falls out and thus a lot of thick and log hairs (terminal hairs) fall out while shampooing or brushing hair. As the disease progresses, the hair follicle begins to shrink leading to the increased number of thin and short hairs (vellus hairs), so that hair loss becomes unnoticeable. Then, the vellus hair finally has full coverage, so that the scalp shows through the thin hair. In every phase, hair fallen out is a club hair*3. The scalp is oily with greasy dandruff and it is seborrheic dermatitis hair loss. It often makes beard, chest hair and extremities hair grow thicker.

  • ※1: Hair follicles surrounding the part of the hair that are deep under the skin consist of cell layers and make hair cells harden and shape into hair.
  • ※2: Period when cell division in the hair matrix in hair cycle completely stops
  • ※3: Physiological hair loss
Skin structure
Hamilton-Ludwig Classification


Androgenic alopecia is known to be an inherited condition. It is caused directly by the shortening of the growth phase of the hair cycle by the action of growth inhibitory factors on hair matrix cells under the influence of androgenic hormones. At that time, dermal papilla cells play an important role. Hair influenced by androgens includes hair on the front and the top of the head, beard, hair in the underarm area and in the pubic area and so on. Hair on the rear of the head and eyebrows are not influenced by androgens. Androgens do not act on hair matrix cells but on dermal papilla cells.
Dermal papilla cells play an important role in hair growth and hair root formation. As hair growth is influenced by androgens, dermal papilla cells have androgen receptors. As androgens control the actions of dermal papilla cells, hair growth is accelerated or inhibited. Moreover, dermal papilla cells contain 5 alpha-reductase which reduces and converts testosterone into more potent hormone, dihydrotestosterone (DHT).
When the DHT enters in the cytoplasm of dermal papilla cell, this enzyme converts testosterone into DHT which binds to the androgen receptor and moves to the nucleus of the cell. The resulting substance controls the gene activities leading to the control of signal sending factor formed by dermal papilla cells. This system is a little bit complicated; 5 alpha-reductase occurs as 2 isozymes, type 1 and type 2; the type-1 isozyme expresses in dermal papilla cells of most hairs, while the type -2 isozyme which is strongly affected by androgens is distributed to the beard and the front and the top of the head. In short, DHT formed by 5 alpha-reductase type 2 hardens beard, while it softens hair on the front and the top of the head.

AR:androgen receptor
5α-R:5 alpha-reductase
HGF:hepatocyte growth factor
IGF-1:insulin-like growth factor 1
TGF-β1:transforming growth factor-beta 1

Countermeasures (treatment)

Androgenic alopecia which is a kind of physical phenomenon (aging phenomenon) occurs in a man with genetic predisposition by actions of androgens. It is difficult to stop the disease progression and return to what it used to be in a man who has already developed the disease. The medical institute makes a diagnosis of the disease and treats complications such as seborrheic dermatitis or seborrheic keratosis, but not androgenic alopecia (finasteride [Propecia1 mg or 0.2 mg] *1 will be prescribed).

The therapeutic goals are as follows (in order of precedence):
1) Inhibit and slow the progression of hair loss.
2) Maintain the current situation
3) Volumize hair

We have often heard of complaints that the hair does not grow at all in spite of the use of a hair growth product. If it can slow the hair loss progression or can maintain the current status, it can be said that it is (at least)worth having used the hair growth product. It is important to use it after understanding its effects well.
Effective treatments (countermeasures) are those that can inhibit the disease progression by oral administration of finasteride and that can volumize hair by using an effective hair growth product with clear mode of actions. In Western countries, oral finasteride (inhibition of softened hair) and topical minoxidil (promotion of hair growth) are commonly used.
In recent research, ultra-narrow band red LED light also attracts considerable attention.

※1 : Inhibits the progression of androgenic alopecia because no growth inhibitory factor in hair matrix cells is induced. This is not a hair-volumizing product. It exerts its effects in 6 months and may show a tendency of volumizing hair in some cases. It is effective for men only but not for women.

Source: New Hair Science
(Japan Hair Science Association)

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