white hair: Why does our hair turn white when we grow old?

The color of hair matters more than you may realize. Beyond its cosmetic role, it also may provide insulation and ward off harmful ultraviolet light. The determination of hair color is complicated. Melanocytes, cells that live in the upper layers of the skin and at the base of hair follicles, produce pigment (called melanin) that creates the coloring of hair. They produce two types of melanin: eumelanin, a brown-black pigment, and pheomelanin, a yellow-red pigment. The genes you inherit from your parents determine the exact mix of pigments that your melanocytes produce, which accounts for the similarity of hair color shared by family members.

Once a hair is produced by a hair follicle, its color does not change 閳?so while a head of hair can turn gray over time, an individual hair doesn't actually turn gray. An individual hair may be pigmented (brown, black, red, blonde), white (because the melanocytes have "run out" of pigment) or gray (when the amount of pigment is reduced). That's why the chemicals and dyes applied to hair may alter its color temporarily, but once the hair has grown out, its true color is again evident at the roots. Ordinarily, gray hairs are hidden among the pigmented hairs, becoming more obvious only as the pigmented hairs fall out over a prolonged period of time. The different texture of gray hair is the result of reduced moisture that accompanies reduced pigment.

Why melanocytes stop producing enough melanin is not entirely clear. Part of it may be related to "apoptosis," a term that means the death of a cell triggered by the cell itself after a certain amount of time. Whatever the reason, melanocytes lose capacity at about 10% to 20% per decade. The first gray hairs may show up in teenage years, but more commonly they appear between ages 35 and 50.

Men gray sooner than women, but the tendency to gray early, late or not at all also depends in part on the genes inherited from parents. One's ethnic background matters as well 閳?there is variability among different populations. For example, Caucasians tend to develop gray hair sooner than Asian or African people. Another mystery: Gray hair generally crops up first at the temples, then the top of the head, spreading out from there to the rest of the scalp.

Hair may seem to become gray faster if the normal process of "shedding" speeds up, and that is just what happens in a relatively common condition called telogen effluvium 閳?instead of losing about 100 hairs per day as is normal, 300 hairs fall out daily. This may be triggered by a significant illness or other major stress to the body. In those situations, a head of hair that was minimally gray becomes more dramatically gray in a short period because more of the darker hairs have fallen.

There are situations in which graying of hair can be reversed. In certain conditions, such as severe eczema or certain infections of the scalp, or after radiation therapy or chemotherapy, hair that was gray may re-grow with its former color. Early in the process of graying, a gray hair may fall out and be replaced with a normally pigmented hair. And melanocytes that are producing little or no melanin in the scalp can be removed and stimulated in the laboratory to make melanin. Together, these observations suggest the aging melanocyte retains the capacity to increase the pigment it makes even after its output starts to decline. Some researchers believe that with a better understanding of how and why gray hair develops, it may be possible to reverse or even prevent it.

Did you know that hair can be turned green by swimming pool water? It's thought that copper in the water or from pipes, or chemicals put in the water to kill algae, can turn hair green. It's more common among frequent swimmers who have blonde, white or gray hair; fortunately it is reversible (though you may have to find another pool until the source of the problem is identified and corrected).

In addition, certain medications or supplements can promote hair loss, revealing more white or gray hair in their wake. Lithium and amphetamines are mentioned as frequent offenders. Vitamin E and echinacea are also reported to cause graying of hair, although I could find no published confirmation in scientific journals or information regarding which dose or duration of therapy has been linked to graying.

The vast majority of people with gray hair have age-related graying. However, sometimes graying of the hair indicates an illness, especially if it occurs at a particularly young age. Several illnesses may be heralded by gray hair, including:

Vitamin B12 deficiency

Neurofibromatosis 閳?Also called Von Recklinghausen's disease, this is a group of inherited diseases in which tumors grow along nerves. Developmental abnormalities may be observed, including that of skin and bones.

Tuberous sclerosis 閳?An unusual, inherited condition associated with benign tumors in multiple organs (including the brain, heart, kidneys, eyes, lung and skin)

Thyroid disease

Vitiligo 閳?A condition of unknown cause in which melanocytes are lost or destroyed 閳?perhaps because the immune system "misfires" and attacks the skin rather than an infection. If the scalp is involved, areas of white hair may develop.

Alopecia areata 閳?Another "autoimmune" disorder in which patches of hair may be suddenly lost, especially the pigmented hairs. This may lead to the "overnight" graying because previously present gray or white hairs suddenly become more obvious. When hair growth resumes, it may be white or gray, but normally pigmented hair may eventually return.

In addition, there is research linking premature graying of hair to other health conditions such as heart disease and low bone mass (called osteopenia), a precursor of osteoporosis, although how they are connected is unclear. Cigarette smoking also has been linked to premature graying.

As with most medical myths, there is an element of truth to the notion that stress can lead to graying hair. For the most part, however, it is untrue. Because a hair shaft cannot change color once it has grown in (unless exposed to chemicals that change its color, a regular event at hair salons), hair cannot suddenly turn gray with or without stress.

However, alopecia areata and telogen effluvium can lead to pigmented hair loss, and stress has long been considered a trigger of these conditions (though not confirmed by recent research). As a result, an emotionally stressful event rarely can trigger loss of darker hair, leaving behind gray and white hair that is suddenly more noticeable. However, this is the exception, not the rule, and even this does not happen literally overnight. Much more often, stress (or lack of stress) has little known effect on one's hair 閳?unless, of course, you're so on edge you pull it out.

How hair grows, ages and changes color over time is a complicated process. While it is possible that stress matters, it is unlikely to play a critical role. Everyone has stress, yet not everyone has gray hair. Current understanding suggests that there are more important influences on the color of hair than stress, worry or anxiety. A host of genetic and environmental influences can affect your hair color, although the precise reason one person's hair turns gray while others never develop gray hair remains a mystery.

As a matter of coincidence, adults often raise their children at about the time that they notice their first gray hairs. But that doesn't mean kids are the cause of their parents' gray hair. There were many things my parents could rightfully blame on me, but turning their hair gray was not one of them. In fact, because hair color and graying may be inherited, it is much more likely that I can blame my gray hair on them.