• Why do so many women go blonde?

    By Emily Sohn, Discovery Channel
    Teen actress and singer Miley Cyrus wowed fans this week by chopping off most of her hair and dying it platinum blonde. Afterwards, she tweeted, "LOVE my hair ♥ feel so happy, pretty, and free."

    With the new 'do, Cyrus joined the throngs of women around the world who choose to go blonde.

    So, what's the appeal?

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    At its root, the desire to have light hair represents an urge to look different, said Peter Frost, an anthropologist at Laval University in Quebec City. Most people have dark hair, so blondes stand out.

    The urge to be blonde may also be driven by deep evolutionary history beginning many millennia ago when light shades first appeared on women's manes, allowing them to turn the heads of potential mates.

    "The more common a hair color becomes, the less often it is preferred," Frost said. "It's a kind of novelty effect. The moment you become ordinary, you no longer have the same appeal. There's selection for being a bit different and eye-catching."

    Modern humans evolved in Africa. Even after migrating to Europe about 35,000 years ago, scientists think that all people had black hair. Then, sometime between 10,000 and 15,000 years ago in northern and eastern Europe, studies suggest, the hair-color gene MC1R developed variations that produced a diversity of hues, including red, brown and blonde.

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    Eye color, which is controlled by several genes, including one called OCA2, diversified at the same time. Some researchers have speculated that lighter hair and eyes helped people better acquire vitamin D in a high-latitude environment. Frost has a different theory.

    During the last Ice Age, he proposes, men had to travel longer distances through Arctic tundra to find animals to hunt. That led to higher death rates for men as well as a decreased chance for polygamy because it would have been nearly impossible to support more than one family with such a scarcity of food.

    As women came to outnumber the supply of monogamous men, they had to become more competitive for male attention. In evolutionary terms, this produced strong sexual selection for novel hair and eye colors. Women with unusually bright looks were eye-catching and appealing.

    Men didn't experience the same pressure, which might explain why it is still more common for women to be born blonde, and why it takes longer for blonde hair to darken on girls than it does on boys.

    Even today, Frost said, the market for blonde hair dye is greater among women in places like Latin America, where naturally light locks are particularly unusual. In Sweden, where a large proportion of people are blonde, women often darken their hair. Purple, magenta and other unusual hues have also become popular.

    In addition to the desire to stand out, going blonde might represent a subconscious attempt to look young and cute. That's because, along with broad foreheads and little noses, blonde hair is also more common in young children than in adults.

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    All of that hair coloring may pay off for women, suggests some research. In a study published in April in The Journal of Socio-Economics, for example, French waitresses earned more money in tips from male customers if they wore blonde wigs.

    Other research, which included more than 12,000 American men using a popular dating website, found that men showed a slight preference for blondes over other hair colors, said Jena Pincott, author of the book, "Do Gentlemen Really Prefer Blondes?: The Science Behind Sex, Love, and Attraction." Polish men have been shown to prefer blonde hair on women who are older than 25, a finding that supports the youthful-look theory.

    For modern women, the benefits might be psychological more than anything else.

    "If being a blonde makes you feel more attractive, you'll be more confident, seek more attention, and likely get it," Pincott said. "Then you'll have more fun."

    Once blonde hair becomes too common, though, it may lose some of its appeal.

    Some research has shown that single men prefer pictures of blonde women if embedded in a series of brunettes. But if the men see mostly blondes, brunettes become more attractive to them. Scandinavian men, who are surrounded by blondes from birth, often say they prefer women with darker hair.

    "Modern men are attracted to blond hair for the same reason as their Ice Age counterparts: It's eye-catching and, much of the time, rarer," Pincott said. But, she added, "Even the most dazzling shade won't help you stand out if everyone has it." 

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  • Stress made Tyra's hair fall out. Why?

    Jamie Mccarthy / Getty Images

    Tyra Banks says the stress from writing her new book gave her alopecia. What's behind the link between stress and hair loss?

    By Cari Nierenberg

    Tyra Banks definitely has a lot on her plate, but she recently complained about having much less on her pate. The "supermodel-turned-mogul" just added "fiction writer" and "New York Times bestselling author" to her ever-growing list of accomplishments.

    But banging out a book and running a multimillion dollar beauty, fashion, and entertainment empire reportedly took a toll on her in an unexpected place -- her scalp.

    Banks let her hair down in a recent Wall Street Journal interview, confessing, "I got a little alopecia from the stress." The stress is the five years it took to write her newly released young-adult book, "Modelland" while juggling her other professional responsibilities. Banks prefaced her comment by admitting, "How can I say this without tearing up?"

    We feel her pain, even though we suspect she could afford to hire a ghost writer to pen the pages.

    Even so, losing the hair on your head -- whether it's temporarily or permanently -- is hard to do, even for the most beautiful and richest among us.

    "Writing a book can definitely be a stressor that can lead to hair loss, or alopecia" says Orr Barak, MD, a dermatologist at Main Line Dermatology in Philadelphia. But in women with hair loss, doctors also have to rule out if the stressor is a thyroid problem or low iron levels. "While these are rarely the causes, it's more commonly an emotional stressor like Tyra is talking about," he points out.

    Barak suspects Banks had "telogen effluvium," a kind of stress-induced hair loss.

    Still, we needed to get to the root of her problem. Our "mane" question (sorry) was: Why does stress cause your tresses to fall out?

    As Barak explains it, a normal head of hair spends 80 percent to 90 percent of its time in the growing phase of the hair cycle, known as anagen, and 10 percent to 20 percent of its time in the resting, or telogen, phase. (An exception to this is pregnancy when the hair cycle increases to 100 percent anagen, or growth.)

    "When the body undergoes a stressor, the hair follicle is affected and a new equilibrium is set for the hair cycle," Barak says. The rate may fall to say, 60 percent of its time in the growing cycle and 40 percent in the resting phase. This down shift causes more hair to fall out, and you see more of it in your brush or shower drain.

    Thankfully, shedding more hair than usual is often temporary. "When the body recovers from stress, hair will get back up to its normal 80 percent to 90 percent ratio of growth over time," notes Barak. We hope that's what happened to Bank's locks.

    Have you noticed more hair loss during an especially stressful time? 

    Related:

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  • Bad hair day? Experts explain curse of the cowlick

    Dan Steinberg / AP

    Cowlicks even strike vampires! "Twilight" star Kristen Stewart has one at the front of her hairline.

    By Cari Nierenberg

    Alfalfa from the "Our Gang" TV serial had a famous one that stuck straight up. So did Dennis the Menace of comic strip fame. Supermodel Claudia Schiffer reportedly has two on her front hairline. "Twilight" star Kristen Stewart has one in front. And in a recent tweet, The Pioneer Woman, Ree Drumond, the blogger turned Food Network TV star wrote, "My cowlick is fired." Channeling her inner-Donald Trump, she perfectly captures how this wayward whorl of hair can drive people crazy.

    Cowlicks seem to have a mind of their own and like to go against the flow.

    The hair on your head needs to go in three directions -- some needs to go forward, some backwards, and some to the sides.

    "In a perfect world, there would be a line so hair would know which way to go," says Dr. Orr Barak, a dermatologist at Tufts Medical Center in Boston. A cowlick is the body's answer to this, by having a centralized location on your scalp -- a crossing point for hair to grow and lie in different directions.

    But an unruly cowlick often selects its own direction -- and pops straight up -- or chooses an angle at odds with your preferred style. That's when the frustration and annoyance sets in.

    A cowlick's spiral pattern is likely caused because hair gets confused about whether it needs to go forward, backward, or to the side, and some hairs get caught in between creating that characteristic whorl, explains Barak. Cowlicks were supposedly named for the swirling pattern made on hair when a cow licked its calves.

    Virtually everybody has a cowlick or two, with the most visible one found at the crown of the head and a second less obvious one, perhaps at the neck or on the front hairline by the part.

    They form early in life -- in utero -- and once you have a cowlick, you're stuck with it unless you lose your hair. Both men and women are equally affected by them, although it doesn't seem that way since they are more noticeable in guys because they typically have shorter hair. 

    Longer styles often camouflages a cowlick because the weight of the hair covers it up. And it's more obvious in straighter hair compared to curly.

    According to Barak, there are some interesting associations between cowlicks and their rotating patterns on your head. He says that noted geneticist Amar Klar has found a connection between handedness and the direction of hair whorls.

    In people who are right handed, at least 90% of cowlicks have a clockwise rotation while about 10% go in a counterclockwise direction.

    Klar's research has found that people who are not righties are more likely to have a counterclockwise cowlick. In one experiment, he found that 50% of folks who are lefties or ambidextrous have a counterclockwise whorl pattern, suggesting that hand preference and cowlick rotation may develop from a common genetic mechanism.

    Interestingly, in a study published in 2004 on nearly 600 men, Klar found that roughly 30% of gay men had a counterclockwise rotation on their scalp hair whorl compared to just 9 percent seen in the population at large.

    No matter how your cowlick swirls, most people would be happy to know how to tame it. Although Barak is a doctor and not a hair stylist, he recommends keeping your hair long or going with the grain of the cowlick. Of course, the right cut and styling products can also do the trick.

    Readers, what seems to work for your cowlicks?

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