The Biology of Hair Color
We know 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.
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.
There are many other 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 but we really don't know for sure why red hair is a common trait among Celts?
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
We might not know the specifics on why hair is a certain color; we do know how hair gets its color. Hair color (pigmentation) is developed by melanocyte cells. These are 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. Interesting to know about Melanocytes:
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 How and Why Hair Grows). 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 research has found that melatonin, a hormone secreted by the pineal gland is secreted 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. 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:
Hair Color and Hair Count
Provided there has been no hair loss beyond the roughly 100 hairs that are lost daily by normal hair cycling there are between 90,000 to 150,000 hairs on the average scalp. Blond hair (blond is not a 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 Color Stereotypes
There are very widely accepted stereotypes associated with hair color; socio-cultural associations with hair color accompany these stereotypes. Some are age-old, others are recent, but all are all are perpetuated by the most frequent culprits in generating cultural stereotypes, television and movies.
Blonds are generally considered to be:
Redheads are generally considered to be:
Brunettes are generally considered to be: Brown hair is an indication of restrained emotion and an even temper.
Brunettes, if female, are wholesome and dependable. The classic television comedy "Gilligan's Island" stereotypically pairs wholesome, dependable brunette Mary Ann with red/blond, ditzy, dumb, seductive movie star Ginger.
Changing Hair Color and Minimizing Damage
Hair color is one of those highly visible characteristics that individualize 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.