Stressed about hair loss

In a study published in the prestigious journal NatureResearchers have found that a stress hormone causes hair loss by keeping the stem cells of the hair follicle in an extended resting phase, which prevents the regeneration of new hair.

It has long been known that chronic stress, whether caused by the stressors of modern life or created in response to illness or trauma, is associated with premature hair loss. Thus, in the current pandemic, about a quarter of people affected by COVID-19 report abnormal hair loss within six months of the onset of disease symptoms (1).

Continuous renovation

The hair follicle is one of the only tissues in the body capable of maintaining an unlimited number of regeneration cycles throughout our lives. This follicle oscillates naturally between growth and rest, a process that is nourished by stem cells present in a bulge at the base of the follicle.

During the growth phase, stem cells are activated to regenerate the hair follicle, which allows for continuous hair growth which thus becomes longer every day.

During the resting phase, the stem cells become inactive and then the hair can fall out more easily. On the other hand, when this resting phase lasts abnormally, fallen hair is not replaced in certain areas of the skull, which can give the hair a sparse appearance.

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Stressed stem cells

The results obtained in animal models suggest that the effect of chronic stress on hair loss is caused precisely by an inhibition of the regenerative function of hair follicle stem cells (2).

The researchers observed that in mice kept under stress, these stem cells remained in the resting phase for a very long time, without regenerating new hair.

This effect is associated with high levels of corticosterone (the human equivalent of cortisol), one of the major stress hormones, and the simple act of administering this hormone to “relaxed” rats was sufficient to reproduce the stress effect on stem cells. .

Through a series of sophisticated experiments, using modern techniques of biochemistry and molecular biology, the researchers showed that corticosterone did not act directly on stem cells, but rather on a class of cells present in the dermis.

By binding to its receptor in these cells, the stress hormone blocks the production of a protein called GAS6 which is normally secreted by the dermis and whose role is to activate hair follicle stem cells to stimulate growth. of hair.

This mechanism seems absolutely essential for hair regeneration, because the use of a virus to produce the GAS6 protein in the dermis is sufficient to activate stem cells and resume hair growth, even in animals subjected to chronic stress.

White hair too!

The same research group recently showed that a similar phenomenon was involved in stress-induced hair graying (3).

In this case, on the other hand, it is the melanocyte stem cells responsible for the production of melanin, the pigment that colors hair.

They showed that under stress conditions, the exaggerated release of norepinephrine caused by overactivity of the sympathetic nervous system leads to a permanent disappearance of the reservoir of melanocyte stem cells present in the hair follicles, resulting in hair color loss.

Premature hair loss or stress-induced graying is definitely not a health risk. On the other hand, they can serve as indicators of the presence of chronic stress conditions and related health problems, especially at the cardiovascular level.

For example, a recent study reports that the risk of myocardial infarction was approximately 5 times higher in people with high cortisol levels (an indicator of stress levels) compared to those with normal cortisol levels (4).

Learn to manage chronic stress, for example by focusing on activities such as regular physical exercise, yoga, meditation, walking in the woods or any other relaxing activity that appreciates the positive aspects of life and minimizes its worries, so there may be only positive consequences on health.

♦ (1) Huang C et al. 6-month outcomes of COVID-19 in hospital-discharged patients: a group study. Lancet 2021; 397: 220-232.

♦ (2) Choi S etj. Corticosterone inhibits GAS6 to govern the calmness of hair follicle stem cells. Naturepublished March 31, 2021.

♦ (3) Zhang B etj. Hyperactivity of sympathetic nerves promotes melanocyte stem cell depletion. Nature 2020; 577: 676-681.

♦ (4) Faresjö T etj. Elevated cortisol levels in the hair precede acute myocardial infarction. Science. Reps. 10published December 31, 2020.

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