Why do we develop grey or white hair?

As people age the pigment cells in their hair follicles that produce melanin die. With the reduced number of pigment cells the new hairs produced become transparent thus appearing grey or white.

Genetics affect the age at which grey hair is developed. A person can get Grey hair earlier if his parents had Grey hair earlier in their lives.

Vitamin Deficiency can accelerate the growth of Grey hair. Vitamins such as B12 and minerals such as Zinc and copper are required to keep the hair healthy and pigmented.

Smoking is known to produce free radicals which in turn cause oxidative stress. This oxidative stress makes melanin less effective in keeping the hair colored.

A poor diet and especially junk food can accelerate the growth of grey hair.

Stress is believed to accelerate the growth of grey hair. (See The body language signs of stress)

Shocks or trauma can make a person's hair turn grey much faster and in a short period of time.

Hormonal imbalance can promote the growth of grey hair and let the hair lose its color faster.

Anemia is known to accelerate the growth of white hair.

If the thyroid gland fails to produce enough hormone, the hair might turn grey faster.

Some commercial products might prevent the hair from getting enough air and as a result, growth of grey hair might be accelerated. (See How to slow down the greying of hair?)

Drinking can accelerate the growth of Grey hair.