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How Does Stress Stop Hair Growth?

When people experience severe stress, they sometimes experience severe hair loss; But scientists did not know exactly why this was happening. 

A new study in mice now offers clues: Stress hormones may stop hair growth.

The follicles, the specific organs from which hair sprouts, have cycles of growth and rest. The follicles first actively produce new hair and then go to sleep.

 In mice, high levels of the stress hormone corticosterone (similar to the human hormone cortisol) keep follicles at rest longer than normal, according to a new study published in the journal Nature. 

This response prevents hair follicles from entering the growth stage, where the stem cells in the follicles produce new hair.

Corticosterone stops hair growth by binding to a receptor on cells beneath the base of each follicle that release chemicals to regulate the hair cycle. 

Once bound to the receptor, this hormone blocks the production of a protein called GAS6.

 Without GAS6, hair follicle stem cells cannot activate and begin hair growth. 

“Instead of directly regulating stem cells, chronic stress affects the expression of stem cell-activating signals , ” Chih Hsu, an associate professor of stem cells and restorative biology at Harvard University and lead author of the study, told LiveScience .

According to Hess, this chain reaction may be slightly different in human hair follicles; But the mechanism can be very similar; Because human corticosterone and cortisol belong to a family of hormones and interact with similar types of receptors. 

“In humans, resting hair can fall out more easily than growth hair, which may explain how stress causes hair loss,” Hsu said.

 “If the findings can be replicated in humans, it must be shown that cortisol can bring growing hair follicles to rest,” said Roy Yi , a professor of pathology and dermatology at Northwestern University School of Medicine in Chicago.

If there is a specific mechanism in mice in humans, Yi said, treatments to prevent stress-induced hair loss could potentially be considered. However, before researching new therapies, scientists must identify differences between the mouse and human models.

In a new study, Hsu and colleagues first stopped the production of stress hormones by removing the adrenal glands in animals. The adrenal glands are endocrine organs that produce stress hormones. 

The hair follicles of these mice entered the growth stage three times more than the untreated control group mice.

 In addition, their resting periods were significantly shorter and lasted less than 20 days compared with normal mice, which lasted 60 to 100 days.

The researchers found that if the mice were fed altered corticosterone, their hair follicle cycle would be similar to that of normal mice. 

This indicates that the hormone suppressed their hair growth in some way. The authors tested the idea in normal mice by intermittently exposing them to mild stressors for nine weeks and found that by increasing corticosterone levels, the animal’s natural hair growth stopped.

By looking at the link between hormone levels and hair growth, the researchers focused on hair follicles to see if corticosterone interacts directly with the stem cells inside. 

This hormone binds to the glucocorticoid receptor; Therefore, the researchers selectively deleted the receptor in various cells that were involved in hair growth and then applied corticosterone to the mice. 

Removal of the receptor from the hair follicle stem cells did not make a difference and the hormone continued to stop hair growth.

When the researchers removed the receptor from adjacent dermal papilla cells, hair growth continued normally without a long resting phase; Therefore, the researchers thought that what stopped hair growth must be related to papillary dermal cells. They found that normal papillary dermal cells stop producing GAS6 when exposed to corticosterone.

 They also found that GAS6 usually binds to hair follicle stem cells and activates them and initiates hair growth; However, without this protein, the hair follicles remain at rest. 

Similarly, direct injection of GAS6 into the skin of mice can stimulate hair growth; Even if the animal is under stress and has high corticosterone levels.

Theoretically, GAS6, or a very similar protein, could stimulate hair growth in stressed humans; But first, several important issues need to be addressed.

 One reason is that although corticosterone and cortisol are chemically similar, we do not know if they play exactly the same role in the human and rodent hair cycles.

 In addition, human and rodent hair cycles have very different schedules. As mice reach maturity, their hair follicles rest longer. By the time a mouse is about 1.5 years old, most of its hair follicles remain dormant most of the time; That is, her hair stops growing.

 About 90% of adult human hair follicles can grow at any given time.

Given that the study in mice only shows how stress hormones can prolong rest and prevent hair growth from resuming, it is interesting to see if cortisol can, in addition to prolonging the resting phase of hair follicles in humans, improve the condition of hair follicles in humans. Take a break that they are actively growing. 

According to Yi, while hair usually falls out at rest, it is not clear exactly why dormant hair does not come off the scalp; Thus, in addition to preventing hair growth, stress may in some ways loosen the hair in place; But this is another mechanism to consider.

While many questions remain unanswered, the mouse study points to potential solutions to stress-induced hair loss that could one day be tested in humans. 

“If the findings are confirmed in humans in the future, manipulations related to the GAS6 pathways may be therapeutic,” Hsu said. 

“Studying mice is the first important step towards developing this treatment.”