For ageing parents, wayward and intractable children may be an obvious reason for gray hair. However, scientifically the questions as to why old age cause hair to turn gray still isn’t very well understood. Let’s start with the basics.

Some terminology
Each hair consists of two parts:

  • shaft— the colored part that we see emerging out of our heads
  • root— the bottom part of hair that fastens the hair under the scalp

Hair grows from head with its root surrounded by a tube of tissues present under the skin known as a hair follicle. Follicles are hollow structures with layers of cells. Actual hair that we see grows from a structure preset at the bottom of the follicle known as a bulb. The color of our hair is determined by a protein called melanin.  Each hair follicle in our head contains a certain number of cells that produces melanin and injects them into the cells that contain keratin. These melanin producing cells are called melanocytes.  Melanocytes also provide colour to our skin.

Reasons Explained

Theory 1 – Production of Toxic Chemicals

For years scientists thought that these melanocyte cells destroyed themselves while undergoing the process of producing melanin. A possible way for this to happen was destruction via toxic  bi-products of producimg melanin; these toxic chemicals generated could damage or even kill melanocytes. (Reference)

This theory came under skepticism for two reasons.

  1. Experiments were carried out on albino mice that have hair similar to humans. Scientists found that these mice did not produce melanin but had melanocytes. This meant that dying of melanocytes over time was not due to toxic waste produced from making melanin as these mice didn’t even produce melanin.
  2. Stem cells – are those special cells that actually make melanocytes. Stem cells convert into melanocytes when the old melanocytes die out.

So, this theory got completely discarded while a few questions remained. Do stem cells stop converting into melanin producing cells or they themselves die? How and why does this happen?

Theory 2- Number of Immature Melanocytes

The second theory rose to answer these questions. Scientists studied the melanocyte cells and founded that young people have more immature melanocytes that reduced as the person aged with none left in elderly people. (Reference)  Now, this could be possible for a number of reasons.

The results in human hair studies showed that as we get older it must be possible that stem cells stop making new melanocytes. Why?

  1. Hair follicles start turning into melanocyte cells faster than the new stem cells are produced. Eventually, the person will run out of stems cells and after sometime will not be able to produce melanocytes.
  2. Stem cells might be programmed by our DNA such that they begin to perish at a certain time and age.

Theory 3 – Presence of Hydrogen Peroxide

Yet another theory says that hydrogen peroxide (a known bleaching agent) is present in our body including hair follicle. In young people an enzyme called catalase breaks this compound into water and oxygen. When the levels of this enzyme decreases and becomes nearly zero, hydrogen peroxide accumulates in the hair follicle becoming difficult to be broken down. Hydrogen peroxide then attacks tyrosinase which ultimately inhibits melanin production.(Reference)

Thanatologists are still studying the different aspects of this process and why it actually occurs.

Other reasons

Age is not the only factor responsible for onset of greying. Consumption of tobacco, smoking, effect of ultraviolet radiations, pollution, lack of certain vitamins in diet, stress and certain autoimmune diseases such as vitiligo and alopecia areata can hinder the working of melanin and induce greying. Genetic defect along with imbalanced hormone levels and premature ageing syndromes such as Hutchinson’s-progeria and Werner syndrome might also be responsible for greying hair as they accelerate every aspect ageing in the body.

Ethnic origin and gender also has to play an important role in greying. According to a study, African Americans begin to gray in their 40’s, Asians in their late 30’s and Caucasians in their mid-30’s. Also, men start graying around the age of 30 and women begin gray around 35 years of age.

Final Strokes

One interesting fact for you in the end, according to the grey hair “rule of thumb” by the age of 50, half of the population losses the color in 50% of their hair. When researchers tested the authenticity of this rule, it came out that 74% of people between 45 and 65 years of age had grey hair, with an average intensity of 27%. (Reference)

Why Does Hair Turn Gray?
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