White Hair: Does Stress Cause Hair to Turn Gray?

The appearance of white hair on the top of the head is completely natural and is part of the many processes characterizing aging. This phenomenon, called canities, usually occurs in the thirties and is due to the gradual decrease in melanin synthesis, the pigment that gives hair its color, by the melanocytes. There are two types of melanin, eumelanin, which is very dark, and pheomelanin, which is lighter. The proportions of these two forms in the hair fibers determine the shade of the hair. Furthermore, the number of melanocytes gradually decreases with age.

Furthermore, the hair growth process involves the synthesis of hydrogen peroxide as a byproduct. This reactive species, capable of triggering a chain reaction leading to the degradation of melanin, is naturally broken down by an enzyme called catalase. However, over time, the amount of catalase in cells decreases, which promotes the degradation of melanin by hydrogen peroxide. Nevertheless, in some cases, graying is said to be premature and is not related to aging.

It is said that, under the influence of stress, Marie Antoinette's hair turned completely white the night before her beheading. While this episode is debated among historians, it aligns with the popular belief that stress can cause hair to turn gray. Myth or reality? Scientists have delved into this question and recently discovered that, under certain circumstances, stress can indeed be a factor in the onset of white hair.

While the underlying mechanisms are only partially understood, several observations and hypotheses have nonetheless been made. Hair growth is an active process that takes place within the hair follicles. It requires a lot of energy, supplied by structures within the cells called mitochondria. During hair growth, the cells receive chemical and electrical signals, emitted by various hormones including cortisol, the stress hormone. Researchers have speculated that these exposures could alter the proteins and other molecules deposited in the growing hair shaft.

Another hypothesis put forward is related to the "fight-or-flight response". When we are subjected to a stressful situation, our body reacts by synthesizing certain catecholamines, including adrenaline, which acts as a neurotransmitter in the central nervous system and as a hormone in the bloodstream. Adrenaline is also capable of binding to receptors on melanocytes to stimulate the synthesis of melanin. The proposed hypothesis is that in the case of high stress, adrenaline would trigger a massive release of melanin. Following this, the melanocytes would cease their activity.

Once hair has turned gray due to stress, can we hope to regain our original color? Researchers have shown that this is possible in certain cases. Indeed, they observed natural repigmentation in 14 individuals who experienced hair graying due to stress. This occurred quite rapidly, with a recoloration rate of about 28% per day. One possible mechanism to explain this repigmentation involves the activation of immature melanocytes or melanoblasts, the precursor cells of melanocytes, outside the hair follicle. These cells would migrate into the hair follicle and produce melanin, thus recoloring the hair.

To avoid seeing your hair turn gray due to stress, the best course of action is to strive for a healthy lifestyle, particularly by regularly engaging in physical activity, surrounding yourself with pleasant people, avoiding addictive substances, and maintaining regular sleep patterns. Yoga or relaxation techniques can also help to foster a sense of calm, which reduces the risk of premature graying.

• RAWNSLEY J. & al. Hair biology: Growth and pigmentation. Facial Plastic Surgery Clinics of North America (2018).

• PHILPOTT M. Watching hair turn grey. eLife (2021).