May 21, 2008
James L. Breeling
Unsolved Mysteries of Hair Color
Why does your hair have color? Why is it blond, brown, red or black? The ultimate answer, of course, is that hair color is genetically determined, the same as skin color. If your parents and earlier ancestors had black skin and black hair, the odds are that you will also have black skin and black hair. Or, if your parents and ancestors had white skin and blond hair, it is very likely that you will also have white skin and blond hair-unless, perhaps, some ancestors with different color skin and hair slipped into your ancestry at some time in the past.
Having said that, the follow-up question is: Why do humans have different skin and hair color? Why don't we all have skin and hair of the same color? The best evidence available to science indicates that humans originated in Africa and migrated from there into the rest of the world over a period of several million years. The only human remains from those millions of years are bones; however, it is hypothesized that these early humans had brown or black skin, since that is the heritage indicated by people living in Africa today. White skin and blond or red hair appears to be a mutational development that occurred within approximately the past 50,000 years, probably in or near Europe. Why did this happen? There is no certain answer to that question yet. However, geneticists who trace human genes throughout human history point out that skin and hair color are traits that are highly likely to respond to the evolutionary pressure of climate. Thus, light-colored skin that synthesizes vitamin D more readily than dark skin in response to sunlight could have conferred a survival advantage in northern climates, where sunlight is weak, as humans moved north along the edge of the retreating glaciers of the Ice Age.1
There are many other abiding mysteries associated with skin and hair color. For example, today we expect to find white skin and red hair concentrated in northern Europe-perhaps a legacy of the red-haired Celts who migrated across Europe thousands of years ago and are well described in writings of Julius Caesar and other Romans. As far as we know, the Celts migrated from east to west, starting from someplace in eastern Europe. Why was red hair a common trait among Celts? No one knows for sure.
Go many thousands of miles further east, into central Asia. In 4,000-year-old burials in the bone-dry Taklamakan Desert, on the western edge of China, red-haired mummies have been found. Who were these red-haired people? No one knows.
How Hair Gets Its Color
The color (pigmentation) of hair is put there by melanocytes, specialized cells that synthesize the pigment melanin. The melanocytes that synthesize melanin for hair are located in the hair follicle. Melanocytes are also distributed throughout the body-in the eyes, the ears, the central nervous system, mucous membranes and skin.
Differences in skin color are largely determined by the reddish-brown to black melanin pigment synthesized by melanocytes in the skin. Differences in eye color are determined by melanocytes located in the eye. Other pigments contributing to skin color or carotenoids (yellow), oxygenated hemoglobin (red) and reduced hemoglobin (blue).
Melanocytes in the hair follicle are active only during the anagen (growth) phase of the hair cycle (see How and Why Hair Grows). No melanin is synthesized during the catagen (degradation) or telogen (resting) phases of the hair cycle.
Two major types of melanin are synthesized by melanocytes that are specialized to synthesize just one type of melanin:
Melanocytes usually synthesize only one form of melanin at a time. The melanin is taken up by structural proteins located in the cortex at the center of the hair shaft (see Hair as a Biologic Fiber). The synthesis of melanin and transfer of melanin into hair shaft proteins is regulated by genetically programmed enzymes and other regulatory molecules. Melanin synthesis is precisely coherent with the activity cycle of melanocytes; when melanocytes are not active they regress into an inactive phase that diminishes the melanocytes in size and brings all melanin synthesis to a halt. Recent investigations have found that melatonin, a hormone secreted by the pineal gland that has many regulatory functions throughout the body, is secreted also in hair follicles. Both pineal and extra-pineal melatonin play a role in hair growth and hair cycling and may have functions in protecting hair follicle DNA from damage induced by potent chemical reactions that occur during anagen phase.4 Variations in hair color shades can be caused by the amount of eumelanin or pheomelanin taken up by the hair shaft proteins, or by the presence in the hair shaft of both types of melanin-for example, in dusky red auburn hair.
More subtle variations in hue and shade may be caused by (1) reflection and refraction of light from internal interfaces of structural proteins in the hair shaft, or (2) reflection or refraction of light from hair-styling chemicals that coat the hair shaft (the "sheen" promised by advertising for hair-styling products). White hair contains no melanin.
Hair Color and Hair Count
There are 90,000 to 150,000 hairs on the scalp, if there has been no hair loss beyond the roughly 100 hairs that are lost daily by normal hair cycling. Blond color is associated with the largest number of scalp hairs (about 140,000 to 150,000), followed by brown (up to 140,000), black (100,000 to 120,000) and red (90,000). Hair count has some effect on how a person chooses to style his/her hair to achieve the maximum appearance of fullness.Hair Color Mythology
The mysteries associated with hair color-e.g., why our hair is black, brown, blond or red-are accompanied by socio-cultural myths about hair color. Some are age-old myths, others are recent, and all are perpetuated by our most potent myth makers, cinema and television. For example:
Changing Hair Color; Minimizing Damage
Hair color is one of those highly visible characteristics that individualizes a person. That's a frequent reason for wanting to change hair color or reinforce and brighten the color that naturally exists.
Change of hair color may lend a characteristic prized because it has charismatic socio-cultural power. It may make a fashion statement. Or, change of hair color may just be a way to put a little excitement in one's life.
For all of those reasons and more, millions of people change hair color every year, using home hair-coloring kits or using the services of a hair-care professional in a salon.
How Hair Coloring Works
Changing the color of hair is a chemical process. The simplest change is to remove all color with a bleaching agent-most commonly, hydrogen peroxide-leaving the hair a featureless white or yellowish white. All other changes of hair color are complex reactions of chemicals in the hair-coloring product with chemicals and biochemicals in hair.
The chemicals in the hair-coloring product have functions in (1) preparing hair to accept the hair dye, (2) altering hair-shaft biology to maximize color change, (3) minimizing chemical damage to the hair shaft, and (4) "setting" the dye to make the color change permanent until the dyed hair is shed in the normal cycling of hair growth.
Chemicals commonly listed on hair-coloring kits include:
|Ammonia, monoethanolamine||Bleaching; making hair fibers swell for better acceptance of dye|
|Disodium phosphate, citric acid||Buffering agent; stabilizing chemical reactions|
|Sodium lauryl sulfate, cocoamide MEA, Oleth-5||Foaming, thickening|
|P-aminophenol, 1-naphthol, P-phenyl-enediamine,4-amino-2-hydroxytoluene||Dye vehicle|
|Propylene glycol, ethanol, glycerin||Dye precursors|
The list is not exhaustive; many other chemicals may be in the formulation of a hair coloring product, depending on the color change to be achieved (see http://www.pgbeautyscience.com).
What Happens to Hair When Its Color is Changed
The hair shaft is a biologic fiber consisting of layers of structured proteins (keratins) and protectives oils (see Hair as a Biologic Fiber). In order for hair color to be changed, the oils have to be partially removed and the keratins that make up the structure of the cortex and the outer protective armor have to be "softened" in order for them to accept the hair dye. The natural oils of the hair shaft are altered or removed by a bleaching agent. These changes in the structural keratins and protective oils make the hair shaft "dryer" and more brittle than it is naturally. While a single hair-color change may not result in irreversible damage, more frequent hair-color changes (e.g., weekly to monthly) may result in irreversible damage such as split ends and dry, hard-to-comb "weathering".
Minimizing Damage from Hair Color Change
Hair damage beyond the damage necessary for effective hair coloring can be caused by:
Health Problems Caused By Hair Coloring
Allergic reactions to hair dyes are rare, but they do occur in some people. Hair-coloring kits usually recommend testing the product on forearm skin before applying it to the scalp. Products for coloring scalp hair should never be used on eyebrows, eyelashes or beards. Questions have been raised regarding the carcinogenic (cancer-causing) potential of hair dyes. Analysis of a large number of studies concluded that there is no evidence of increased risk for cancer associated with use of hair dyes.5
1. Cavalli-Sforza LL. The Great Human Diasporas. New York: Addison-Wesley Publishing Co.; 1995: 300 pages.
2. Slominski A, Wortsman J, Plonka PM et al. Hair follicle pigmentation. Journal of Investigative Dermatology 2005; 124:13-21.
3. Kowicki J, Quevedo WC, Prota G, Fitzgerald TB. Biology of melanocytes. In: Fitzgerald's Dermatology in General Medicine, 5th ed. Freedberg IM et al, eds. New York:McGraw-Hill, 1999: 192-220.
4. Fischer TW, Slominski A, Tobin DJ, Paus R. Melatonin and the hair follicle. Journal of Pineal . 2008; 44:1-15.
5. Takkouche B, Etminan M, Montes-Martinez A. Personal use of hair dyes and risk of cancer: a meta-analysis. Journal of the American Medical Association 2005; 293:2516-2525.
6. Draelos ZD: Hair Care: An Illustrated Dermatologic Handbook. Taylor & Francis, New York, 2005