What Are the Causes of Greying Hair?

Over time, most people's hair turns grey, according to a report from the Library of Congress. The odds of going grey increase by 10 to 20 percent every 10 years past the age of 30. In the womb, all hair is white and develops its color as the body matures and begins to manufacture melanin, the ingredient that gives hair its natural color. In addition to natural processes, a number of other factors cause greying hair.

Time

As the aging process reduces the amount of melanin produced in the body, new hair grows in without as much pigment, eventually turning grey or white. The rate at which the melanin slows down is primarily driven by genetics. Grey hair signifies a declining amount of melanin, while white hair indicates that melanin production in the hair follicles has ceased. The lack of melanin also decreases the amount of moisture in the hair resulting in grey hair that is dry and wiry. Premature grey hair runs in families, leading researchers to believe that heredity influences the timing of when grey hair first appears. The gene for melanin production has yet to be identified.

Illness

According to a report in InteliHealth, a medical report reviewed by doctors at the Harvard Medical School, a number of diseases can contribute to greying hair. A disease called Werner's syndrome that causes premature aging in patients as young as 20 can cause grey hair as the system goes through the entire aging process. Vitamin B12 deficiency resulting in some forms of anemia are associated with low melanin production. Thyroid conditions and immune deficiencies that attack melanin production also can play a part in greying hair.

Shock

When the body receives a shock from surgery, a high fever or other illness, psychological trauma or sudden, extreme weight loss, the hair follicles can be affected, resulting in a condition called telogen effluvium. While the average healthy person loses about 100 hairs a day in the natural process of hair growth, a person with telogen effluvium can lose more than 300 hairs per day. Older people who contract the condition usually have grey hair coming in. When massive amounts of hair fall our at once, the grey hair becomes more noticeable, leading to the conclusion the person went grey "overnight," or in a very short period of time.