Greying of Hairs

Hair colour is produced by cells known as melanocytes, which migrate into the hair bulb as the hair follicles develop in utero. The melanocytes produce pigment that is incorporated into the growing hair fibres to produce hair in a different array of natural shades.

Hair colour depends on the presence and ratios of two groups of melanins: eumelanins (brown and black pigments) and pheomelanins (red and yellow pigments). While variations in the ratio of these pigments can produce an large number of colours and tones, siblings often have strikingly similar hair colour.

Hair colour varies according to body site, with eyelashes being darkest because they contain high levels of eumalanin. Scalp hair is usually lighter than pubic hair, which often has a red tinge, due to the presence of more phaeomelanin pigments. A red tinge is also common in underarm and beard hair, even in people with essentially brown hair on their scalp.

Hair greying is an eventual and irreversible reality of life and is often associated with growing old. he root of every hair strand under the scalp is surrounded by a tube of hair tissue called hair follicle which contains pigment cells. These pigment cells produce the chemical called melanin that gives the hair strand its colour - black, brown, blonde, red et al. 

When a person grows older, these pigment cells begin to die and the melanin production reduces too, making the strand less colourful and more transparent - grey, silver or white. And that is why hair greying is associated with age.
Even though genetics and hereditary factors play a major role in determining the time of your hair turning grey. 

Causes:
A number of medical conditions as well as lifestyle choices have been related to premature greying of hair. 

Medical Conditions:

• Thyroid Disease: An underactive or overactive thyroid can affect the melanin production in the hair which can cause premature greying.

• B12 Deficiency: Deficiency of B12 has also been linked to premature greying of hair.

• Vitiligo: Vitiligo is a disease that is caused when the pigment producing cells in your skin and hair are damaged. Once the cells in your scalp are damaged, melanin production is reduced  and hair begins to turn grey

It is advisable to see a doctor if you experience premature greying of hair and have a reason to believe that it is not hereditary. This is essential so that you can rule out these serious disorders that have caused early hair greying. 
While some medical conditions are the cause for premature greying of hair, it is not always the case. There are a number of lifestyle choices too that have been related to it.