Stress, Neurogenic Inflammation and Hair Loss.
Andrea Marliani, Paolo Gigli e Daniele Campo
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.
Capsures inhibits Neurogenic inflammation ad avoid Psychogenetic Alopecia�
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