July 28, 2008
James L. Breeling
Why does hair become gray, or completely white, as a person ages?
The phenomenon of graying is so customary that it is often accepted as a fact of life, with little thought given as to why it happens. But there are some questions we can ask:
Why does hair turn gray?
Why do some people experience graying of hair beginning as early as their 20s, while others do not begin to gray until age 40 or later?
Can anything be done to prevent, slow or reverse the graying of hair?
Is graying an indication of unhealthy hair?
Is gray hair harder to style than hair that still retains its natural color?
Can gray or white hair be safely dyed to artificially restore color?
What Gives Hair Its Color?
Hair gets its color from pigments called melanins. The melanins are synthesized in specialized cells called melanocytes inside the hair follicle. (See Hair Color: Biology, Mythology and Chemistry). The melanocytes produce two types of melanin: eumelanin that colors hair brown or black, and pheomelanin that colors hair blond or red (See Hair Science: How and Why Hair Grows).
After release from melanocytes, the melanins migrate into the hair shaft and bind to the keratins that give the hair shaft its strength and structure. Melanin enters the hair shaft when a hair is forming during the anagen (growth) phase. Melanocytes continue to supply melanin to a growing hair throughout the 3 to 7 years that a hair remains in anagen phase.
What Happens to Make Hair Turn Gray?
The normal process of graying is associated with the process of aging.
Not All Graying of Hair is "Normal"
While we usually associate graying of hair with advancing age, there are a variety of other causes for loss of hair color. For example:
- Metabolic conditions such as thyroid dysfunction;
- Autoimmune disease such as multiple sclerosis;
- Certain viral diseases;
- Congenital conditions that often include physical anomalies;
- Long-term starvation or vitamin deficiencies; and,
- Toxic environmental exposures.
What is there about aging that causes hair to turn gray or white? No definitive answer has been found to that question, but there is good evidence to support several hypotheses:
1. Genetically controlled "biological clock" signals tell melanocytes when to stop producing melanin. (See Genes, Hair Growth and Hair Loss: What We Know and Don't Know). The clock sends its "stop" signal earlier in life for some people, later in life for others. (See What Are Biological Clocks?).
2. Gradual accumulation of biological and environmental damage to melanocytes eventually causes the melanocytes to stop producing melanin. Other body cells are similarly affected. This is the cellular damage hypothesis of aging-a hypothesis that has gained increasing support over the last 40-plus years.1 This "free radical theory of aging", first proposed in 1956, states that aging is caused by an accumulation of damage to cells by molecules called "free radicals". These are biochemically hyperactive molecules that are normal metabolic byproducts. They are capable of causing significant damage to cells. Most of these hyperactive molecules are mopped up by other sentinal molecules that are constantly on patrol for free radicals. If the patrolling molecules are inactivated or the output of free radicals is substantially increased, the free radicals can bind with cellular structures and cause cellular damage. Accumulated cellular damage from free radicals is proposed as a major cause of aging. An increase in free radicals can also come from the environment; cigaret smoking is one of the most important sources of free radicals.
3. Genetic signaling influenced by environmental factors causes melanocytes to stop producing melanin, and hair gradually becomes unpigmented-that is, becomes gray and eventually white.
What Are Biological Clocks?
All living organisms on Earth have biological clocks that are on/off switches for essential biological functions. Most of these clocks work at the cellular and sub-cellular level and we are unaware of their activity, although we eventually experience the result of their activity in processes such as aging.
- A biological clock that influences our daily life, in ways we can't help but notice, is circadian rhythm, which puts humans and all other living organisms in tune with the 24-hour periodicity of the Earth's rotation. Our sleep-wake cycle is set by the circadian clock. When we travel several time zones away from home very rapidly, with no time to adjust the circadian clock, we suffer "jet lag" and our sleep-wake cycle is maladjusted for several days. Circadian cycles have been identified in numerous metabolic activities such as release of hormones on a 24-hour sleep/wake cyclic pattern.2
- Apoptosis is a process that tells aging or damaged cells when to die-an important monitoring function that maintains an organism's biological equilibrium. (See http://www.nih.gov/sigs/aig/Aboutapo.html). Ability to evade apoptosis is one of the cardinal features of cancer cells. Dysfunctional apoptosis was recently proposed as a cause of hair graying. Investigators found that dysfunctional apoptosis results in defective self-maintenance of melanocyte stem cells, leading eventually to depletion of the hair follicle's melanocyte population.3
- A genetically-regulated, age-associated signal-a "melanocyte clock"-has been proposed as a cause of age-associated hair graying. Investigators suggested that melanocyte aging may be associated with "free radical" damage to melanocytes, which are subsequently subject to death by apoptosis. Interestingly, these investigators also hypothesized , on the basis of work with animals, that mutations in melanocyte signaling could allow melanocytes to survive apoptosis and recover their function. Melanocytes that recover their function could, possibly, regain the ability to produce melanin and reverse the process of hair graying.4
- Telomere shortening occurs at the ends of chromosomes, the biological housing for genes. The shortening of telomeres, specialized structures at the ends of chromosomes, has been associated with the process of aging.5
As melanocytes shut down their production of melanin, hair will gradually lose its pigmentation and will grow out as "gray". A hair will grow out as "white" when pigmentation is completely absent. The melanocyte diminishes in size as it stops producing melanin; it will eventually become entirely nonfunctional.
Can Something Be Done to Prevent, Slow or Reverse the Graying of Hair?
The cause of hair graying is not definitively identified. Although the possibility of reversing the process of graying has been suggested3, there is no known intervention by which the graying of hair associated with aging can be prevented, slowed or reversed.
Is Gray Hair healthy Hair?
Gray hair has diminished pigmentation, but otherwise remains as healthy as pigmented hair. It may, however, have less natural lubrication than pigmented hair. This is due to a decline in function of sebaceous (oil-producing) cells in the hair follicle that often accompanies decline in function of melanocytes. Diminished lubrication of the hair shaft can make it more subject to damage from brushing and combing and more difficult to style.
Can Gray or White Hair Be Safely Dyed to Artificially Restore Color?
Gray and white hair can be safely dyed to restore an appearance of naturally pigmented hair. It is understandable that most people with gray or white hair would like the dyed hair to have the appearance of naturally pigmented hair. The appearance to be avoided is that of "a bad dye job". (See Healthy Hair).
One approach to dyeing gray or white hair is to put the task in the hands of an experienced cosmetologist in a beauty salon. The client and the cosmetologist can work together to achieve the desired appearance, and to maintain the appearance with the passage of time.
Dyeing gray or white hair at home is more effective and less likely to result in hair damage if the task is approached with certain points in mind:
- Gray and white hair is dryer than pigmented hair due to less lubrication from oil-producing cells in the hair follicle. Because it is poorly lubricated, gray and white hair is subject to breakage from excessive handling.
- Gray and white hair is less easily penetrated by dye chemicals than is pigmented hair. Hair dye may have to be left on gray and white hair longer than it is left on pigmented hair. However, leaving dye chemicals on hair longer can result in hair damage.
- Growing hair (hair in anagen phase) will "show its roots" within a few weeks of being dyed. Gray or white hair that has been dyed should not be re-dyed more often than every 3 to 4 weeks, even if "the roots show". Although touch-up hair coloring can be time-consuming, touch-up of undyed "roots" can decrease risk of damaging hair by too-frequent re-dyeing.
- Achieving a natural appearance of dyed gray or white hair that remains natural-appearing over time and holds up to multiple shampooing may require some experimentation. Different brands of hair dye may have different results. The level of hair dye-temporary, semi-permanent or permanent-will have different effects and different appearance with passage of time.
1. Harman D. Aging: a theory based on free radical and radiation chemistry. Journal of Gerontology 1956; 11:298-300.
2. Wager-Smith K, Kay SA. Circadian rhythm genetics: from flies to mice to humans. 2000; 26:23-27.
3. Nishimura EK, Granter SR, Fisher DE. Mechanisms of hair graying: incomplete melanocyte stem cell maintenance in the niche. Science 2005; 307:720-724.
4. Tobin DJ, Paus R. Graying: gerontobiology of the hair follicle pigmentary unit. Experimental Gerontology 2001: 36:29-54.
5. Finkel T, Serrano M, Blasco MA. The common biology of cancer and ageing. Nature 2007: 448:767-774. by James L. Breeling