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For many years, perhaps for even several decades, stress has
been indicated as a possible cause of hair loss though, to tell
the truth, there is no real proof of this.
Some patients under stress show widespread hair loss, which is
more noticeable in the central area just in front of the crown,
while hair growth continues along the front hairline. Marino Salin
calls this "incidenza nervosa"
This fact is well known to all those who are actively involved in hair care. But how it happens is not clear to anyone.
Biological response to stress usually takes place by way of
the hypothalamus-hypophysis-surrenal gland axis. There is however
another mode, involving a large number of interrelated peripheral
neurotransmitters and hormones which are released by the non-myelinic
nerve fibres of the skin and have a direct effect on the way an
organism reacts to stress.
Psychological or physical stress sets off a chain of molecular
reactions. It does this by way of the Nerve Growth Factor, the
Substance P and Catecholamins. These are all key players which
limit hair growth.
let us see: each hair follicle has a rich nervous plexus. It's important and interesting to know that this follicular nervous plexus is directly connected with the cerebral cortex.
The follicular nervous plexus is partly composed of motor fibres
but it is mainly composed of sensory fibres and also of sympathetic
non-myelinic noradrenergic free ended fibres.
Stimulated by Nerve Growth Factor, which increases under stress,
the sensory fibres are able to liberate Substance P. Substance
P is considered the main pain signal transmitter from the periphery
to the nerve centres. Substance P attracts inflammation mediators.
Substance P causes macrophage and mast cell degranulation with
production of inflammatory cytokines from lymphocytes leading
to induction and inhibition of the keratinocyte proliferation
in the follicle and in the hair matrix and a videomicroscope will
show a clear depressed erythematous ring around the infundibula.
We are talking about neurogenic inflammation. Daniele Campo
calls it "Psychogenetic Alopecia". For patients, who
have no family history of Androgenetic Alopecia and show widespread
hair loss which is more noticeable in the central area, just in
the front of the crown, while hair growth continues along the
front hairline, we need to consider a diagnosis of "Psychogenetic
Alopecia".
Let us now consider the perifollicular sympathetic plexus. The
sympathetic plexus is able to release noradrenaline into the intercellular
perifollicular spaces and noradrenaline is a powerful vasoconstrictor
and inhibitor of the adenil cyclase enzyme. If the adenil cyclase
enzyme is inhibited or completely blocked the entire kinase system
chain is slowed down and glycolysis, the pentose phosphate shunt
and the Krebs cycle are also slowed down, if not completely blocked.
If glycolysis stops, the hair's energetic metabolism is blocked
and so are the mitoses of the hair matrix. The interruption of
glucose metabolism turns off the supply of energy and ends the
anagen phase. As we saw earlier, the sympathetic plexus is able
to release noradrenaline into the intercellular and perifollicular
spaces, The visible, and well-known, effect is horripilation.
But if there is excess adrenergic tone in the metabolic system,
then there is also vasoconstriction, ischemia and hypoxia and
if there is hypoxia, glycolysis leads to lactic acid.
The system's pH is lowered, and the Krebs cycle (which has an
ideal pH of 7.35) becomes slow and incapable of disposing of pyruvic
and lactic acids and, as in a hypoxic and tired muscle, there
is an increase in lactic acid. In these conditions, using a microscope
in polarized light, a large number of hairs which have been removed
for trichogram examination, will have a strange image.
There is damage to the anchoring system of the inner sheath. According to Marino Salin it is lactic acid that causes caustic damage to the inner sheath and this sheath seems to be raised above the hair cuticle.
Lactic acid leads to degradation of the inner sheath because of the caustic effect. Hair loss, in the form of Telogen Effluvium, is the result.
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