The emergence of white hair is primarily caused by a gradual loss of activity in the melanocytes within the hair bulb. When this does not receive enough pigment, it grows in a white shade. The following question then arises: when do the first white hairs appear?
First white hairs: when do they appear?
The first grey hairs are typically visible around theage of 34. This inevitable and natural phenomenon is called "canities". It is characterised by a discolouration of the hair, which turns white over time. We are not all equal when it comes to the onset of grey hair. Numerous factors impact the age at which grey hair appears, and it happens that some people see their hair turn white as early as their twenties, while others still have naturally coloured hair into their fifties.
From birth, melanocytes, located at the base of the epidermis, synthesise melanin, the pigment that controls hair colour. The melanin is then transferred to the keratinocytes via melanosomes. Keratinocytes are the cells that surround the dermal papilla of the hair follicle. The distribution of melanin in the keratinocytes determines the colour of the hair. However, the activity and number of melanocytes decrease gradually over time. Therefore, the amount of melanin synthesised becomes weaker, which causes the hair to turn white.
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 normally naturally degraded by an enzyme called catalase. However, over time, the amount of catalase in the cells decreases, which promotes the degradation of melanin by hydrogen peroxide.
What factors influence the onset of white hair?
The appearance of white hair is thus caused by a decrease in melanin synthesis and a lower distribution of this pigment in the hair fibres. The most common cause is ageing. Like most cells in the body, melanocytes have a limited lifespan. Once these cells disappear, the hair is no longer pigmented and turns white. Several factors are responsible for accelerating or slowing down this process.
The age at which our first grey hairs appear is largely dictated by genetics. Studies have shown that individuals 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 linked to the onset of grey hair, among which is the MC1R gene (MelanCortin 1 Receptor). One or more mutations on this gene can accelerate or slow down the greying of hair.
Pollution , UV rays from the sun, and smoking are factors that cause oxidative stress in cells. In practical terms, this results in the excessive generation of free radicals in the cells of the skin and hair. Indeed, free radicals are responsible for the degradation of melanin, the pigment that colours the skin and hair, through a cascade of reactions. Therefore, they promote the appearance of white hair.
Some autoimmune diseases.
Vitiligo is an acquired autoimmune disease characterised by white patches on the skin (leucoderma) and depigmentation of hair or fur. It occurs when the immune system attacks the melanocytes, which then die or become unable to function.
Stress or emotional shocks.
Chronic stress can be a contributing factor to the early onset of white hair. Studies have suggested that prolonged exposure to stress can disrupt the functioning of melanocytes, the cells responsible for the production of melanin, thus resulting in a decrease in hair pigmentation.
Some deficiencies in vitamins or nutrients.
Deficiencies in vitamin B12, vitamin D, vitamin B9, selenium, iron or copper can impact hair colour and cause premature greying. The mechanisms involved are diverse and depend on the nutrient in question. For instance, copper promotes the activity of tyrosinase, the enzyme that enables the conversion of tyrosine into melanin. Selenium and zinc, on the other hand, are antioxidants that protect melanin from free radicals.
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).