Hair Loss (AGA / FPHL)
What Is AGA?
AGA (Androgenetic Alopecia) is a form of hair loss that gradually progresses after puberty and is characterized by miniaturization, in which changes in the hair cycle make the hair thin and short.
Normal hair follicles repeat the hair cycle of
growth phase (anagen)
regression phase (catagen)
resting phase (telogen)
but in AGA, because the growth phase shortens and the proportion of resting-phase follicles increases, the hair gradually becomes thinner and shorter, ultimately becoming so small that it does not appear on the skin surface.
This phenomenon is seen in both men and women, but there are differences between the sexes in the pattern of hair loss and the age of onset.
Epidemiology
AGA is one of the most common forms of hair loss.
In Japanese men, the prevalence rises with age:
20s: about 10%
30s: about 20%
40s: about 30%
50s and older: about 40%
and the average across all ages is reported to be about 30%.
Similar hair loss is also seen in women, but unlike in men, it shows a pattern in which the hair thins over a relatively wide area of the crown, and cases developing after menopause increase.
Genetics
The development of AGA involves genetic factors and the action of male hormones.
As a genetic background, multiple gene regions are known to be associated, such as the androgen receptor gene (on the X chromosome) and the autosomal regions 17q21 and 20p11.
Therefore, when there is a family history, the risk of developing it is considered to be higher.
Pathophysiology
The male hormone testosterone is converted within the hair follicle into dihydrotestosterone (DHT) by 5α-reductase. When DHT binds to the androgen receptors of the dermal papilla cells, factors such as TGF-β and DKK1 are induced, and the proliferation of the hair matrix cells is suppressed.
As a result,
shortening of the hair cycle
→ miniaturization of the hair follicles
→ softening of the hair
→ progression of hair loss
are thought to occur.
Male Pattern Hair Loss
In men,
a receding hairline at the front
thinning at the crown
is the characteristic pattern of hair loss seen.
In many cases, it begins to become noticeable from the late 20s to the 30s and gradually progresses with age.
Learn more about male pattern hair loss
Female Pattern Hair Loss (FPHL)
In women, unlike in men, it is observed as a pattern in which hair density decreases over a relatively wide area, centered on the crown.
The time of onset also differs from men, with a tendency to increase after menopause.
Male pattern hair loss is understood as an androgen-dependent condition, but in women it is thought that the condition cannot always be fully explained by male-hormone dependence alone.
In light of these differences in the condition between men and women, it has now become internationally common to refer to female hair loss by the name Female Pattern Hair Loss (FPHL).
The clinical guidelines of the Japanese Dermatological Association also take these differences in the condition into account and use the name Female Pattern Hair Loss (FPHL) for female hair loss.
Learn more about female pattern hair loss
Diagnosis
AGA is diagnosed by confirming the progression of the hair loss and the family history, and by visually confirming the miniaturization in which the hair at the front and crown becomes thin and short.
Also, trichoscopy (magnified observation of the hair and scalp) using a magnifier or dermoscope can confirm findings such as variation in hair diameter, so it can be useful for distinguishing from other forms of hair loss, such as alopecia areata and telogen effluvium.
Treatment
Oral and topical medications are used to treat AGA.
For male pattern hair loss,
oral finasteride
oral dutasteride
topical minoxidil
and others are widely used.
For female pattern hair loss,
topical minoxidil
is the mainstay of treatment.
Because hair loss is progressive, it is important to start treatment early and continue it.