White hair: what is the role of oxidative stress?

Free radicals are unstable molecules that carry a positive or negative electrical charge in their outer orbital, meaning they have an unpaired electron. To stabilise themselves, they seek to acquire an electron from another molecule (protein, lipid, DNA...) by reacting with it. These reactions cause cellular damage and physiological disturbances at various levels of the body, including in the melanocytes.

Free radicals are naturally produced within cells during chemical reactions, particularly within the mitochondrial respiratory chain. This complex of protein structures involves a series of oxidation reactions that consume oxygen and produce derivatives: reactive oxygen species (ROS). Under so-called physiological conditions, the production of ROS remains low and only concerns a small percentage of the oxygen captured by respiration. However, certain environmental factors such as pollution, UV rays, cigarette smoke, and alcohol also generate free radicals. When the body's antioxidant defence systems are overwhelmed and can no longer neutralise them, an unstable imbalance occurs: this is referred to as oxidative stress.

Grey hair typically begins to appear around the age of 35, in response to the gradual decrease in the number and activity of melanocytes, the cells responsible for the production of melanin. This pigment, also present in the skin, is what gives hair its colour. Its absence results in white hair. Alongside the aforementioned decreases, the melanocytes in the hair bulb can be affected by oxidative stress. Several clinical studies have shown that free radicals can target and damage these cells. One such study, conducted with over 600 volunteers, particularly demonstrated a link between smoking, a factor of oxidative stress, and the early onset of grey hair.

As previously stated, free radicals can damage cellular components. Themitochondrial DNA, the intracellular organelles essential for cell function, is particularly susceptible. Free radicals cause mutations in this DNA, specifically deletions, meaning a loss of genetic material. This impacts the activity of the mitochondria, which in turn affects the melanin synthesis process by melanocytes and accelerates the onset of white hair.

Oxidative stress also has an impact on the Bcl-2 family molecules. Predominantly expressed in the mitochondria, these molecules protect them from free radicals and the ensuing apoptosis. However, Bcl-2 molecules themselves are sensitive to oxidative stress, which initiates a vicious cycle. Free radicals attack the Bcl-2 in the mitochondria, which then become increasingly sensitive to oxidative stress as the quantities of Bcl-2 decrease. Catalase and superoxide dismutase, endogenous antioxidant enzymes, are not spared and can also suffer damage from free radicals. Furthermore, it should be noted that tyrosinase, the enzyme catalysing the oxidation of tyrosine into melanin, sees its activity decrease in the presence of oxidative stress.

Finally, researchers have observed an ectopic differentiation of melanoblasts in the hair follicle in response to damage caused by oxidative stress. Melanoblasts are the undifferentiated precursor cells of melanocytes. When they differentiate, they acquire their function of melanin production. Following this observation, scientists have suggested that the untimely ectopic differentiation of melanocyte stem cells in the hair follicles reduces the stock of stem cells. The cellular renewal of melanocytes then loses efficiency, which accelerates greying.

To combat oxidative stress and the onset of white hair, it is recommended to increase your intake of antioxidants. Several solutions exist: diet, dietary supplements, cosmetics... However, caution is advised regarding the second option: before starting a course, we advise you to seek advice from your general practitioner. As for antioxidants provided by diet, the most common are vitamins A, C and E, zinc and selenium. There is an index to evaluate the antioxidant power of foods: the ORAC index (Oxygen Radical Absorbance Capacity). The higher it is, the better the food's ability to absorb free radicals. A normal diet averages 2000 ORAC units per day. To reduce oxidative stress, the ideal would be to reach 3000 to 5000 units. The table below includes some foods among those with the highest antioxidant potential.

Even though further studies on this subject are still necessary, it can also be assumed that the use of hair cosmetics rich in antioxidant actives can help slow down hair whitening. Among the most commonly used in formulation are vitamins A, C and E, coenzyme Q10, resveratrol, caffeine, green tea extract, turmeric and ginseng.

Important : Protecting oneself from oxidative stress also involves avoiding its sources, particularly UV rays. It is therefore recommended not to expose oneself to the sun for prolonged periods, especially during the hottest hours of the day.

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