The horror when we see white hair!!!
Black, brown, red, blonde – varying shades of hair color are present in humans. But as we grow old, they all turn white. Our genes play a role in when “canities” or greying of hair begins.
But why does our hair turn grey with age?
Special cells called melanocytes control our hair color by producing a pigment called melanin. Two types of melanin are eumelanin (dark brown or black) and pheomelanin (reddish-yellow). The melanocytes arise from melanocyte stem cells (MeSCs) located in the hair follicle– a tiny sac from where hair grows. The hair growth cycle has three phases-
- active growth (anagen)
- degeneration (catagen)
- and rest (telogen)
Under normal conditions, melanocytes originate from some MeSCs during anagen and die during catagen and telogen. A reserve of MeSCs creates more melanocytes in the next anagen phase. With age, however, MeSCs gradually decrease in number reducing melanin in our hair. Thus, hairs look salt and pepper-colored.
Stress and Hair
Anecdotally, hair greying is always associated with mental stress. According to a legend, before execution at the guillotine, the hair of Marie Antoinette turned white overnight! In reality, the relation between stress and grey hair is not very clear. But stress can trigger hair loss in a condition called telogen effluvium. The hair that grows back may be grey if the person is middle-aged.
Searching the Link
In a new study, the research team led by Dr. Ya-Chieh Hsu of Harvard University demonstrated that acute stress in black mice causes their fur to go grey. Mice were exposed to three types of stresses-
- restricted movement,
- psychological stress
- and stress by pain (achieved through an injection of resiniferatoxin– a chemical similar to capsaicin in chili peppers).
Each type of stress caused loss of melanocyte stem cells (MeSCs) forming patches of white hair. Since all MeSCs were exhausted, greying was permanent.
Fight-or-Flight
Next, scientists tried to find out how stress caused MeSCs loss. The first possibility was that the immune system could attack MeSCs due to stress. However, experiments in mice with weak immune systems still showed hair greying. The stress also increased levels of two hormones- corticosterone and noradrenaline in mice. Using different methods, researchers concluded that there was no link between corticosterone and hair greying. However, when they prevented the interaction between MeSCs and noradrenaline (through loss of receptors on MeSCs), hair greying was completely blocked during stress. They also injected noradrenaline directly under the skin, and fur around the site of the injection turned white.
The next step was to find the source of noradrenaline. Adrenal glands are the chief producers of noradrenaline but greying occurred even after their removal. Under stress, the “fight-or-flight” response causes a part of the nervous system called the sympathetic nervous system (SNS) to secrete noradrenaline in hair follicles. The researchers were able to prevent greying by destroying the sympathetic nervous system or by blocking the release of noradrenaline from it. They also showed that activating the SNS, even in the absence of stress, drives loss of MeSCs. Each type of stress caused loss of melanocyte stem cells (MeSCs) forming patches of white hair. Since all MeSCs were exhausted, greying was permanent.
Together, the team’s experiments showed that noradrenaline released from sympathetic neurons triggers MeSCs to develop and migrate quickly. Thus no more MeSCs were left for the next anagen cycle. To confirm this result, the researchers suppressed growth of MeSCs under stress and the hairs formed in the subsequent cycles were colored.
Does this apply to Humans?…… We don’t know. Although the treatment of cultured human melanocyte cells with noradrenaline led to the induction of growth in cells, we still need to find out more. But these findings will benefit in discovering how stress affects the body as the sympathetic nervous system is associated with almost all organs.
Greying in Humans
Another study from a research team led by Martin Picard at Columbia University offers quantitative proof that links psychological stress to hair greying in humans. The team has created a new method to measure hair pigmentation patterns (HPPs) in greying and transitional (dark to white/white to dark) hairs. This method is similar to rings in a tree trunk that hold information about its life in previous decades. When hairs are still under the skin, they are influenced by things happening in the body. Once hairs grow out of the scalp, they become hard in structure and the color is permanent.
Our hairs look like they are the same color throughout but this technique helped to quantify greying by capturing images of tiny slices of human hairs. Each slice is 1/20th of a millimeter wide which represents about an hour of hair growth. It can precisely correlate times of stress with hair color on a single hair strand. The researchers studied individual hairs from 14 volunteers. They also measured the levels of various proteins in hairs and found that about 300 proteins altered when the hair color changed. Then they developed a mathematical model suggesting that changes in mitochondria due to stress may explain how hair turns grey.
The Reversal
What surprised the researchers was that greying could be naturally reversed in people by eliminating stress. It differs from the previous study in mice in which stress-induced greying was permanent, indicating that a different mechanism may be involved. The participants also rated their stress levels over the past one year. The analysis revealed a striking relation between stress and hair greying. A 30-year-old Asian female showed greying followed by a rapid and complete reversal that synchronized with the time of marital conflict, separation and relocation. Reversal of five hairs of a 35-year-old Caucasian male coincided with stress decline after a 2-week vacation.
Is Reducing Stress Enough?
Reducing stress has many benefits but your hair won’t necessarily return to normal. According to the model, there is a threshold before which hair doesn’t turn grey. For example, a 5-year-old cannot develop grey hair due to stress. But stress can trigger greying in middle age when we are near that threshold. Similarly, grey hairs in a 70-year-old who is far above the threshold, aren’t affected by reducing stress.
These findings reveal that greying can be halted or reversed—at least temporarily and that human ageing isn’t linear. But due to the small sample size, the study of more participants over a long period is needed (prospective cohort study).
These two studies provide a breakthrough in understanding how stress can influence cells leading to hair greying and ways in which we may be able to stop the damaging effects of stress on our body.
References
- Zhang, B., Ma, S., Rachmin, I. et al. Hyperactivation of sympathetic nerves drives depletion of melanocyte stem cells. Nature 577, 676–681 (2020). https://doi.org/10.1038/s41586-020-1935-3
- Rosenberg, A. M., Rausser, S., Ren, J., Mosharov, E. V., Sturm, G., Ogden, R. T., Patel, P., Kumar Soni, R., Lacefield, C., Tobin, D. J., Paus, R., & Picard, M. (2021). Quantitative mapping of human hair greying and reversal in relation to life stress. eLife, 10, e67437. https://doi.org/10.7554/eLife.67437