Every hair on the head has two important parts. One is shaft which we see as a part growing out and the second one is root, which is present under our scalp and it always firmly holds the hair. A group of tissue surrounds the root of every hair which is known as the hair follicle. These contain pigment cells varying in numbers and it produces melanin, a chemical that is responsible for the color of our skin whether a person will look fair or dark. Same way it is responsible for the color of hair which totally depends on the quantity of melanin present in each hair follicle and hence determines the color, brown, red, blonde etc.
This pigment cells present in hair follicle starts dying with the age. The less melanin present in hair follicle the lighter is the color of hair like white, silver, and gray Because now the root does not have enough melanin to retain the dark color of hair.
Hair turns gray not in old age but also in young age it may be in 30â€™s and 40â€™s or it can be in 20â€™s too. In these cases hair turn gray due to genetic reasons which means that a child hair will start turning to gray nearly at the age when their parents or grandparents had experienced their first gray hair. It took nearly ten years for all the hair to turn gray from the time when we have seen the first gray hair.
Genetics is the most common reason for gray hair but other causes are also more or less responsible for e.g. poor health, intake of less nutritious things, anemia, lack vitamin B, thyroid disorders etc. smoking is also one cause for hair to turn gray because it reduces the oxygen present in the tissues of our body.
Person getting treatment for aids or cancer will also have to face with the problem of gray hair. Some people think that shock, tension, stress are also responsible but scientists do not approve this. It may also occur because of climatic conditions and pollution.