The science behind hair graying


Figure 1 – Explora. ¿Por qué nos salen las canas? Reprinted from https://www.explora.cl/blog/por-que-nos-salen-canas



We all remember that moment when we spot the first silver hair. Confusion comes and leaves a lot of questions. What causes hair to turn gray? Why do grays appear so early at times, while in other people after their thirties? Is it true that if I pluck one, seven more will grow?


Oxidative stress is the key factor to blame. During all our life we are exposed to different internal and external sources that promote reactive oxygen species production. With the years, the production of these species increases while the defense mechanisms that the body uses to combat them decrease. This imbalance is known as oxidative stress and it can affect the body normal functioning.


Hair color is determined by two types of pigments: eumelanins and pheomelanins. Eumelanins provide dark brown and black colors while pheomelanins produce orange and red colors. The ratio of these melanins defines the color that our hair and skin have. With age, oxidative stress occurs and leads to a reduction in the synthesis of melanins, giving our hair a gray appearance (1).


A research reveals that gray hair on average first appears in the mid-thirties in Caucasians, in the late-thirties for Asians, and mid-forties in Africans. Women usually start graying at the boundaries of the scalp, while in men graying is first noticed in the temples and sideburns (2). However, an average is an average, and several factors influence the timing of the appearance of gray hair.


Genetics is considered to play a major role in when and how hair graying is developed. Stress and smoking have been connected to go gray earlier (3). Another feature to take into account is the nutritional state: obesity, low antioxidant intake, vitamin B12 deficiency as well as some illnesses including thyroid disturbances, vitiligo and alopecia areata can promote a loss of pigment in your hair (4) (5). There are conflicting research studies on the incidence that UV light has on hair graying and further investigation is needed to gain a better understanding (2) (3).


Now that you understand how and why gray hair is in your life, you should know that there are some myths and misinformation about the topic. First of all, you do not go gray overnight. Some studies have shown that unpigmented hair grows approximately 10% faster than pigmented hair (6). What this means is that gray hairs appear more than they actually are, and esthetically accentuate the slow process closely related to the hair cycle. Furthermore, it is not a reversible process: there is no scientific evidence that age-induced hair graying can be reverted. Another common misbelief is that plucking one gray hair will cause seven to grow in the same place.


So, how do we stop or delay graying of hair? A well-balanced diet and a healthy lifestyle can help, (1) but at present there are no other definitive treatments so do not be fooled by false promises.




(1) Trüeb, R. M., The impact of oxidative stress on hair. Int. J. Cosmet. Sci. 2015, 37, 25-30.

(2) Kumar A.B. et al. Premature Graying of Hair: Review with Updates. Int. J. Trichology. 2018, 10(5), 198–203.

(3) Jo S.K. et al. Three Streams for the Mechanism of Hair Graying. Ann Dermatol. 2018, 30(4), 397–401.

(4) Hirt P.A. et al., Skin changes in the obese patient. J. Am. Acad. Dermatol. 2019, 81 (5), 1037-1057

(5) Harvard medical school. Why does hair turn gray? https://www.health.harvard.edu/blog/hair-turn-gray-2017091812226 (accessed Nov 9,2019)

(6) Kaplan P.D. et al. Grey hair: Clinical investigation into changes in hair fibres with loss of pigmentation in a photoprotected population Int J Cosmet Sci. 2011, 33, 171-182.


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