Canities: Misconceptions about white hair.

"Getting grey hair" is not just an expression. Stress can indeed accelerate the greying process. While the underlying mechanisms are not yet fully understood, it appears that certain hormones released in stressful situations can disrupt the activity of melanocytes, and therefore the production of melanin. To avoid seeing your hair turn grey prematurely, it is necessary to try as much as possible to manage your stress. Yoga or certain relaxation exercises, for example, can help you feel more at ease.

This is both true and false. In fact, it depends on the cause of the white hair. If your white hair is due to ageing, and therefore a decrease in the number and activity of melanocytes, this is an irreversible phenomenon and your hair will not be able to naturally regain its original colour. Similarly, if the cause is a chronic disease, greying cannot be reversed.

Nevertheless, if stress is the cause of your grey hair, a recent study has shown that it may be possible for it to naturally regain its colour. Indeed, scientists have observed in 14 individuals a depigmentation of their hair fibres due to a period of intense stress, followed by a fairly rapid repigmentation, of approximately 28% per day.

This is a common misconception. Pulling out a white hair does not affect the ability of melanocytes to produce melanin in other follicles. Furthermore, hair grows according to an independent growth cycle for each follicle, with phases of growth (anagen phase), rest (catagen phase) and shedding (telogen phase). When a hair is plucked, the cycle of other hair follicles is not disrupted.

Inspired by Marie-Antoinette, Thomas MORE, and Jean GABIN, the myth of the sudden greying is a popular belief. Indeed, a growth cycle (anagen phase) lasts from 2 to 7 years. Knowing this, it is impossible for hair to turn entirely white overnight. One hypothesis to explain the sudden greying reported in history is as follows: it would be an autoimmune reaction, triggered by an emotional shock.

This is a unique and rare case of alopecia where the immune system mistakenly attacks only the hair follicles that produce coloured hair. This attack triggers inflammation that disrupts the growth cycle of coloured hair and causes it to fall out. Therefore, it's not that the entire head of hair turns white, but rather the coloured hair is lost and the white hair remains, creating an optical illusion.

It is often true, white hair is more fragile than coloured hair. The lack of melanin in their cortex, the intermediate layer of the hair fibre, is the cause of this characteristic. Indeed, melanin does not only play an aesthetic role, but it also protects the hair, particularly from oxidative stress caused by UV rays or pollution.

It's true. The age at which our first grey hairs appear is largely dictated by genetics. Studies have shown that people of so-called Caucasian type generally see their hair turn grey in their early thirties, those of so-called Asian type notice it in their late thirties, and those of so-called African type see it during their forties. Several genes are involved, such as the MC1R gene or the IRF4 gene. One or more mutations on these genes can accelerate or slow down the greying of hair.

This is a myth. Pregnancy itself is not linked to greying hair. However, the stress caused by childbirth or the prospect of raising a child can accelerate the onset of white hair.

It's true ! Deficiencies in vitamin B12, vitamin D, vitamin B9, selenium, iron or copper can affect hair colour and cause premature greying. The underlying mechanisms are varied and depend on the nutrient in question.

For instance, selenium and zinc are antioxidants that protect melanin from free radicals. Copper, on the other hand, promotes the activity of tyrosinase, the enzyme that facilitates the conversion of tyrosine into melanin.

The sun promotes the lightening of hair and is indirectly involved in greying. Indeed, the UV rays it emits generate free radicals, reactive species which a study has shown promote hair whitening. Free radicals are indeed involved in several mechanisms leading to the degradation of melanin and damage to melanocytes. The sun therefore contributes to the appearance of white hair.

One might think so because white hair is almost devoid of melanin, which offers a wider range of colouring options. However, due to their fragility, white hair is not easier to colour. Indeed, the scales, which make up the hair cuticle, lose cohesion over time and loosen. The hair then becomes more porous, while the fixation and retention of dye pigments become more challenging.

This is false ! No colour gradient can be observed on a hair strand. When it grows, it is either coloured or white. More specifically, when the melanocytes in the hair bulb no longer produce enough melanin to be incorporated into the hair's keratin, the hair grows completely white. Therefore, a white hair grows white from its root and does not gradually become white as it lengthens.

Not always. Depending on the proportion of white hair on your head, it's not necessarily required to use hair dye to hide them. A simple highlight on a few strands is sometimes enough. You can also adapt your hairstyle to camouflage your white hair or use an accessory, such as a headband or a scarf.

This is generally false. White hair does not appear at the same rate all over the scalp. It is often observed that the first white hairs are located at the temples. It can also happen that they are grouped in a specific area of the hair, forming a visible streak of white hair. All of this contributes to the fact that the transition between coloured hair and white hair can be difficult to manage.

It's true. White hair can easily turn yellow. Several causes have been suggested to explain this phenomenon, among which is the oxidation of residual melanin. This oxidation leads to a change in the chemical structure of the melanin, resulting in a yellow colour. All hair shades can be affected by this phenomenon, but it is more visible on white hair for colourimetric reasons. Indeed, if you add white and yellow, you get a yellowish colour, whereas if you add brown and yellow, you get more of a light chestnut.

• SEIBERG M. Age-induced hair greying - the multiple effects of oxidative stress. International Journal of Cosmetic Science (2013).

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