White Hair: Does stress cause hair to turn grey?

The emergence of white hair on the crown of the head is entirely natural and is part of the many processes characterising ageing. This phenomenon, known as canities, typically occurs in one's thirties and is due to the gradual decrease in melanin synthesis, the pigment that gives hair its colour, 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 fibres determine the shade of the hair. Furthermore, the number of melanocytes gradually decreases with age.

Furthermore, the process of hair growth involves the synthesis of hydrogen peroxide as a by-product. 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, greying is said to be premature and is not related to ageing.

It is said that, under the influence of stress, Marie Antoinette's hair turned 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 grey. 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 suggested 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 synthesising 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 in melanocytes to stimulate the synthesis of melanin. The proposed hypothesis is that in the event of high stress, adrenaline would trigger a very significant release of melanin. Following this, the melanocytes would cease their activity.

Once hair has turned grey due to stress, can we hope to regain our original colour? Researchers have shown that this is possible in certain cases. Indeed, they observed natural repigmentation in 14 individuals who had seen their hair turn grey under the effects of 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 recolouring the hair.

To prevent one's hair from greying due to stress, the best course of action is to strive for a healthy lifestyle, particularly by regularly engaging in sports, surrounding oneself 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 greying.

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

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