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Why does hair know when it needs to stop to grow


I'm still not quite sure if head hair grows endlessly, or if it stops at some point, but that's not the question.

When the hair on my leg grows, it obviously doesn't grow endlessly, but it also stops at some point. I learnt that hair is dead matter, so why does the body know that my hair reached maximum length, and realizes I cut it when I did?


That's an awesome question! Let me help you rephrase, as I don't have a direct answer; why does hair stop growing at certain lengths, and differentially at various locations on the body?

There are three stages to hair growth:

  • Anagen phase- growth
  • Catagen phase- transition
  • Telogen phase- rest
  • (then falls out!)

You're asking why and how the anagen phase stops, or more concisely, what processes cause anagen phase to cease and proceed to transition to a degenerated rest.

The indirect answer I have for you is this: there doesn't exist a definitive mechanism for how the the telogen phase is induced- that is to say that the process by which the hair-producing follicle "turns off" it's cycle to come to a halt has not yet been fully elucidated in the literature and remains a discovery to be made.

I hope I've helped you understand your targeted question


The Big Question: Why Does Hair Grow in Some Places But Not Others?

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Tweeze, shave, chemical cream, wax or electro-zap: Humans have come up with a pharmacy's worth of ways to deforest their bodies of natural hair.

Yet, to evolutionary biologists, humans are amazing not because they have so much hair, but because they have so little. Whereas our ancestors once sported full-fur suits, Homo sapiens today are almost embarrassingly naked.

The story of how our bodies morphed from being upholstered in head-to-toe carpeting into a mosaic of hairy and non-hairy bits is one of sweat, sex, scent, and (not to be left out) climate change.

Early hominids (our über-great grandparents), the story goes, made their living foraging for fruits, nuts, tubers, and vegetation in the cool shade of forest trees. Then, about three million years ago, a global cooling period dried out the regions of Central Africa where those early family members were living.

The fur that had once kept them warm became a liability, as forests changed into grasslands and early hunters spent long hours striding or running across the savanna in pursuit of dinner. From natural selection's point of view, the ability to sweat and quickly dissipate heat became the neatest trick on the block. So, by and large, humans lost their hair.

What that did, says Russell Tuttle, anthropologist and evolutionary biologist at the University of Chicago and author of Apes and Human Evolution, is give humans the ability to be out hunting in the heat of the day when other predators (i.e. LIONS!) "are resting and trying to keep themselves cool, because all they can do is pant."

If that evolutionary argument doesn't convince you, that's fine. But just consider the alternatives, like the charming but ridiculous "Aquatic Ape Hypothesis" that's occasionally bandied about the scientific literature. Advocates think early hominids went through a phase of near-total water living and, like dolphins and whales, lost the bulk of their hair in order to reduce drag. Unfortunately, there is no particular reason to believe this is true.

Happily though, the gods of evaporative cooling didn't demand the sacrifice of all our pilatory plumage. We've still got some hair left, and it (mostly) seems to serve a purpose---starting with the most highly-groomed bits.

Like your eyebrows, for example. Aside from being good for raising, furrowing, and piercing, the hair there keeps the sweat out of your eyes. And the hair on your head shields your noggin from the direct force of the sun. It also leaves an area of air between your scalp and hair's hot surface, so sweat can evaporate and cool things down. (Curly hair, Tuttle says, does the best job at performing this task.) Head hair grows longer than other hair because these follicles remain in an active growth (or anagen) phase longer than other other hair follicles---generally a couple of years instead of just a couple of months.

That hair's useful. But what about all the soft, downy stuff that barely shows up on your body? It's called vellus hair, and it's a safe bet that it's an evolutionary relic. Humans don't need it anymore, but it's not doing any harm either, so there it stays. Vellus hair is closely related to another type of hair that definitely serves a purpose, though. Add just a little androgenic hormone (which starts circulating in both boys and girls around puberty) and *voila---*it becomes thicker and darker.

You knew we were going to get here, didn't you? Hair follicles in certain favorite regions of our body are differentially sensitive to androgens---along with other places, like lower legs, arms, and chests. Put another way, our hair gets dark and thick only in some places. And that so-called androgenic hair's placement probably developed over millennia in response to humans' behavioral needs.

Don't tell the multi-billion dollar deodorant and perfume industry, but humans actually like how other humans smell. Our hairiest regions carry two kinds of sweat glands. There are eccrine glands, which are found on most of the body and open directly to the surface of the skin (needed for cooling), and apocrine glands, exclusive to the hairiest bits, which empty body odor-carrying fluid into the hair follicles.


The Four Hair Growth Stages

Like your skin, nails and other parts of your body, your hair constantly goes through a complex, multi-stage growth process.

It’s important to understand that your hair is made up of two separate structures, each of which plays a role in its growth.

The first of these is the hair follicle, which lies under the surface of your scalp. Your hair follicles are living structures that produce new hairs through a complex process involving the creation of new cells.

The second structure is the hair shaft. This is the part of your hair that grows out from your skin.

Each hair shaft grows from the hair bulb -- an area of the hair follicle that converts nutrients into the keratinized cells that make up your hair.

The hair growth process (or hair growth cycle, as it’s often referred to in medical literature) has three distinct stages:

  • The anagen (growth) phase . This is the active growing phase, during which your hair grows to its full length.
  • The catagen (regression) phase . This phase marks a transition of the hair from active growth into a resting phase.
  • The telogen (resting) phase . During this phase, your hair follicle becomes dormant and doesn’t actively grow.

Many hair growth experts also include a fourth phase in this process, which is referred to as the exogen, or shedding, phase.

During this phase, the hair fiber detaches from the hair follicle, allowing a new hair to grow from the follicle in its place.

Each stage of the hair growth cycle lasts for a different amount of time, meaning your hairs may grow for years before entering the catagen, telogen and exogen phases.

Below, we’ve explained each hair growth phase in more detail to help you better understand the hair growth process.

The Anagen (Growing) Phase

During the anagen phase, your hair actively and continuously grows. About 85 to 90 percent of your hairs are in this stage at any one time.

All of the hair on your body goes through the anagen phase, although the duration of this phase can vary depending on the location of hair on your body.

On average, your scalp hair grows for between two and six years before reaching the end of the anagen phase. In comparison, the anagen phase for thigh hair is around two months.

This variation in the length of the anagen phase is the reason why the hair on your scalp is able to grow to a much longer length than the hair on your face and body.

The Catagen (Regression) Phase

After it passes through the anagen phase, each hair follicle enters the catagen phase. Referred to as the regression or transition phase, this period of the growth cycle involves the formation of a club hair -- a hair shaft that’s detached from the blood supply of the follicle.

During the catagen phase, your hair stops actively growing and the hair follicle, which previously supplied the hair with nutrients, shrinks slightly. This phase lasts for several weeks.

The Telogen (Resting) Phase

During the telogen phase, your hair follicle rests. The hair shaft also remains in a resting state, with no ongoing growth.

Between 10 and 15 percent of the hairs on your scalp, face and body are in this phase at any given time.

Like the anagen phase, the telogen phase varies in length. Most body hair has a short telogen phase that only lasts for a few weeks, while scalp hair can go through a telogen phase of up to one year.

Certain health issues, such as stress, infections or illnesses that cause fever, may cause your hair to prematurely enter the telogen phase of its growth cycle, resulting in a form of hair loss that’s referred to as telogen effluvium.

The Exogen (Shedding) Phase

As new hair starts to grow from the hair follicle, the old hair enters into the exogen phase, or shedding phase.

During this phase, the hair fiber detaches from your scalp and falls out. It’s normal to shed about 50 to 100 hairs every day through this process.

You may notice these hairs on your pillowcase, in your hairbrush or stuck inside your shower drain.

Since each hair is replaced by a new one growing from the same follicle, the hair shedding that occurs in the exogen phase doesn’t contribute to male pattern baldness.

More hair. there's a pill for that.


How Common is Female Hair Loss?

Just like male hair loss, female hair loss becomes more common with age. Studies show that only 12% of women between the ages of 20 and 29 show some degree of hair loss, from loss around the hairline or temples to diffuse, overall thinning.

On the other hand, women aged 80 and up have a more than 60% chance of experiencing some degree of hormonal hair loss. Because hormonal hair loss is partly caused by a genetic sensitivity to DHT, your risk of hair loss could be higher if your mother, siblings or other female relatives have hair loss.

If you’re concerned about hair loss, it’s important to take action quickly. Because hair loss is gradual and affected by DHT, acting quickly allows you to minimize hair loss and maintain as much of your hair as possible.

Choices to help keep your hair healthy and full


You Asked: Why Is My Hair Falling Out?

F irst, let&rsquos debunk a few myths: Shampooing, brushing and towel drying your hair aren’t making it fall out. &ldquoPeople associate these things with hair loss because they see the hair come away. But these aren&rsquot the cause,&rdquo says Dr. Melissa Piliang, a dermatologist with the Cleveland Clinic. In fact, Piliang says shampooing less frequently may make things worse. &ldquoIt can lead to dandruff and scalp inflammation, which can exacerbate hair loss,&rdquo she says.

Hats and ponytails also get a bum rap. &ldquoIf a ponytail is worn so tightly it pulls on your eyes, that could damage your hair and lead to breakage,&rdquo Piliang acknowledges, adding that tight braiding, extensions and weaves&mdashwhich yank on small groups of hair follicles&mdashcan also cause problems. &ldquoBut generally wearing a ponytail or a hat won&rsquot cause hair loss,&rdquo she says.

Men and women lose their hair for different and interrelated reasons, ranging from genetic factors to a poor diet, says Dr. Adam Friedman, director of dermatologic research at the Montefiore-Albert Einstein College of Medicine in New York. &ldquoIt&rsquos rare for hair loss to be caused by just one thing,&rdquo he says.

To understand these causes, it&rsquos helpful to know how your hair works. Similar to the way your skin&rsquos cells turn over, your hair is constantly sprouting, growing and falling out. Guys with healthy hair shed between 60 to 80 follicles a day, while women lose roughly 100, Friedman says.

When it comes to male- and female-pattern baldness&mdashthe most common types of hair loss&mdashcertain hairs grow in shorter and shorter over time, and eventually stop growing back at all. This is usually the result of a genetic sensitivity to hormones in the skin, Friedman says. &ldquoIn men, you see this most in the front and sides of the scalp,&rdquo he explains. &ldquoIn women, it&rsquos more centrally located and diffuse.&rdquo Friedman says this is a slow process, one that can take years to become apparent.

For these people, drugs that block the production of skin hormones or keep hairs from falling out&mdashsuch as minoxidil and finasteride&mdashtend to work well, Friedman says. But both are better at stopping hair loss than they are at regrowing hair. &ldquoIf you&rsquore bald and want treatment, there&rsquos often not much you can do,&rdquo he says. For this reason, it&rsquos imperative that you see a doctor as soon as you notice a problem.

Poor nutrition is another potential contributing factor. Friedman says low levels of iron, vitamin D, some B vitamins and zinc have all been linked to hair loss. While typically not the main cause of your thinning mane, nutrient or vitamin deficiencies can make the problem worse, he says. Fixing your diet or taking supplements can help, but it&rsquos often just one part of a multifaceted solution.

If clumps come out when you shower or you notice thinning in just a few weeks or months, you&rsquore more likely dealing with another common condition called acute telogen effluvium, Piliang says. This rapid hair loss is basically a short-term ramping up of your hair&rsquos normal shedding process.

Any event that puts a lot of stress on your body&mdashlike childbirth, surgery or rapid weight loss&mdashcan result in this alarming, clumpy hair loss, which tends to start a couple months after the event, Piliang says. The shedding can last for six months and may result in your losing up to 70% of your hair. But typically the hair grows back, she explains.

There are many more explanations for hair loss, including scalp infections, inflammatory diseases like alopecia areata, or systemic diseases like lupus. Treatments vary widely and may include a combination of oral or topical drugs, light therapy, dietary changes, and stress-reducing interventions. You really need an expert’s help to assemble all the puzzle pieces, says Dr. Laurel Schwartz, a dermatologist in private practice at the Philadelphia Institute of Dermatology.

If you&rsquore experiencing skin irritation, redness, scaling or pain, Schwartz recommends seeing someone ASAP to head off risks like permanent hair loss and scarring.

More good advice: Stay away from &ldquomiracle&rdquo cures marketed online or in late-night TV infomercials. They&rsquore not the answer. &ldquoHair loss is such an emotionally charged experience,” Schwartz says. “And when you&rsquore really upset, you&rsquore willing to try anything.” Time spent experimenting with different over-the-counter or infomercial products is often time (and money) wasted.

Your hair can offer a glimpse of what&rsquos going on in the rest of the body, Schwartz says. &ldquoIf you notice a problem, discuss it with a doctor to determine the ultimate cause.&rdquo


What Causes Hair Shedding?

"There can be a number of causes genetics is the primary reason for men and many women," says Michelle Blaisure, trichologist and Bosley Professional Strength product and technical specialist. But many women commonly experience hair shedding thanks to stress and lack of nutrients (like vitamins B, D, and zinc). "Another common reason for excess hair fall is hormonal changes, particularly in women," Burg adds. "These can happen with pregnancy, childbirth, a change in contraceptive pill, or during menopause. The change in hormones can affect the way hair grows by shortening the growth part of the hair cycle, leading to increased fall."

According to trichologist and colorist Bridgette Hill of Paul Labrecque Salon and Skincare Spa, you should be concerned if you're seeing one of the following ailments:

  • You seem to leave trails of hairs in the car, pillow, or just from running your fingers through your hair when not brushing or combing.
  • When shampooing and noticing larger amounts of hair in the drain.
  • A sudden decrease in density or thickness in ponytail or hair over a 3-6 month period.

But don't panic: Burg says this is completely reversible. "This sort of phenomenon is referred to as telogen effluvium, which just means that a group of hairs has stopped growing at the same time and then have shed together," he explains. Also, your hair and nails take a lot of energy to grow—but they're not a top priority for your body, which is why you may experience shedding during times of physical and emotional stress. Read on to find out more tips on how to stop hair shedding.


A common cause of hair loss in the legs is peripheral artery disease (PAD), which is poor circulation caused by the buildup of plaque and narrowing of the arteries that supply blood to the legs and feet. Hair loss occurs because the impaired blood supply is not able to provide optimal nutrients for hair growth. According to the Centers for Disease Control and Prevention (CDC), 12 to 20 percent of adults over the age of 60 have PAD, a condition more common in smokers, and in people with diabetes, heart disease, high cholesterol and high blood pressure. Other physical symptoms of PAD include smooth, shiny skin and a cooler skin temperature.

Anterolateral leg alopecia, a seemingly harmless cause of lower leg hair loss, is common in middle-aged and elderly men, according to the April-June 2014 issue of "International Journal of Trichology." Alopecia areata is an autoimmune disease that causes round patches of hair loss, often the size of a quarter, which can occur anywhere on the body. A more severe but rare form of this condition, called alopecia universalis, causes hair loss all over the body.

Some other diseases can cause hair to stop growing, although most of this hair loss is not specific to the legs. For example, thyroid disorders or severe malnutrition caused by illness or eating disorders can cause hair loss all over the body.


Why It Feels So Good to Chop off Your Own Hair

It had been a particularly stressful week when, scissors in one hand and four inches of hair in another, I decided to cut. A few snips later, I felt triumphant. Sure, a week from then I paid an expert to fix it. But in that moment, I felt like a weight had been lifted, and that felt good, even if it was just a few ounces.

Why We Impulsively Cut Our Hair

This is something you’ve probably done at some point, too, quite possibly right after a breakup. It’s not just heartbreak, however, that inspires us to chop. “I’ve found that people typically have an impulse to cut their hair after they’ve experienced stressful situations, positive or negative, where things have felt somewhat out of their control,” said Dr. Lauren Appio, a psychologist and career coach in Manhattan.

There are practical reasons for wanting to impulsively cut your own hair, of course, but that’s not what we’re talking about here. We’re talking about that impulsive urge to just get rid of it. Appio says people often feel the urge to impulsively cut their hair when they’re bored or “stuck in some way.” In my example, I’ve been trying to finish a book with a hard due date, which means I’ve had to stick to a strict, focused writing regimen for weeks. I craved something new. Novelty feels good, after all, and it can even make you more productive .

But why hair? Appio said: “Making a significant change to your appearance can be soothing because you can see the immediate results of your actions, which reminds you of the power and agency you have in your life.”

Hair is also symbolic. As unimportant as it may seem—“it’s just hair, it grows back, y’know ,” a friend once said when I wavered over shaving my head like hers—our hair is tied to who we are.

“Hairstyle is often a signifier of gender and culture,” Appio told me. “Changing a hairstyle may reflect our desire to affirm our connection to our communities, or, alternatively, to challenge cultural or societal norms related to appearance and presentation.”

For example, at the New Statesman , Laurie Penny explains her decision to wear her hair very short:

Among the plus points for short hair is that makes it easier to read my book on the bus in peace. I mention this because there are clearly some men who rarely or never consider what it’s like for a person to negotiate femininity in the real world. Choosing to behave consciously as if the sexual attention of men is not my top priority has made more of a difference to how my life has turned out than I ever imagined.

In other words, hair is subtly tied to our choices and thus, our identity, which is why changing it can feel so damn good.

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Why You Should (or Shouldn’t) Do It

Admittedly, spontaneously lopping off my hair isn’t a new concept to me. I spent 2010-2014 growing out a botched, impulsive cut. Sometimes it feels great other times I’ve regretted it. From a psychological perspective, though, isn’t impulsive behavior usually frowned upon? I asked Appio. “If you haven’t looked at the needs you may have that are creating these urges, it’s likely you’ll continue to re-experience a cycle of having strong urges, feeling the buildup of tension or excess energy, and releasing that tension by acting on your urge,” she said.

There’s a case to be made for the impulsive cut, and we’ll get to that, but first, there are a few reasons why you might want to step away from the scissors and reassess your urge:

  • The novelty wears off: The novelty of a new haircut can wear off quickly—then you might be stuck with a cut you don’t like or one that requires too much work. I straighten my hair every time I wash it now, and I don’t enjoy doing that.
  • You might not know what you’re doing: It’s easy to screw up your own hair, especially if you don’t have straight, fine hair. My hair is thick and half-straight, half-wavy, which means it needs an expert’s touch (and even experts often screw it up.)
  • It can distract you from more important matters: “Generally, I encourage people to respond rather than react to their urges,” Appio said. “To determine whether a behavior is helpful or unhelpful, it’s important to consider how it functions for you. For example, you can explore how it will serve you to cut your hair or otherwise act on the urge you’re experiencing, and how acting on this urge might get in your way.” Fair enough. Also, keep in mind—the impulsive decision to cut your hair is often accompanied by days of obsessing over why it’s “just not right.”

That said, cutting your hair on a whim can be a perfectly fine way to deal with tension, too. It can just be a mildly adventurous experience worth having. Here’s why:

  • It’s liberating: Again, that feeling of getting rid of the old and embracing something new feels cathartic. It also feels good to take control. Hair seems like a silly thing to feel in control over, but sometimes the simple act of making a decision, even a silly one, can make you feel more powerful.
  • Change is good:Novelty can be a great thing . It can make you more productive, motivated, and creative.
  • It’s just hair: Yes, hair is symbolic of your identity, but a symbol is just that: a representation of something else. Your hair, as a symbol, is not the actual thing that defines you. When you screw up your hair, you remember this.

“People who tend to be perfectionistic or indecisive due to overthinking can benefit from trying out more spontaneous behavior. It can be illuminating to see that you can survive and even enjoy the outcome of making a quick or imperfect decision,” Appio added. “At best, it is a way to be creative, take pleasure in your appearance, and try something new with minimal risk.”

Like the bangs you’re thinking of cutting, I’ll put it bluntly: even if you screw up your hair, it might still feel good and at the end of the day, my friend was right. It’ll grow back, y’know ?

Questions to Ask Before You Chop

Let’s say you’re leaning toward the “I’m gonna do it” camp but you’re still wavering. If you want to put a little more thought into your decision, ask yourself some questions.

Have you done this before? What was your experience? I get the urge to chop often and asking this question always reminds me of how frustrating my past hair experiences were and most of the time, I realize the aftermath outweighs my desire for change. Appio suggests a few others:

  • What needs am I trying to meet by cutting my hair or otherwise engaging in the urge I have? For example, do I have a need to feel more grounded or in control?
  • What do I risk by making this change, and am I willing to accept those risks?
  • Are there other, more effective ways for me to meet the needs I have?

Another good question: Are you drunk? When you’re bored and buzzed, regrettable decisions often follow. Also, from a practical standpoint, think about whether you have any events coming up, like a wedding, party, or networking thing. You might want to allow your drastic cut some time to grow in before you go to a big public event. Or you just might not feel like hearing, “Omg you cut your hair?!” every five minutes.

If You’re Going to Do It, Here’s How

Okay, you’ve decided: it’s time to cut. It’s probably best to go to a salon and enlist the help of a professional, but I also understand that this takes half the adventure and drama out of the situation. (Mulan didn’t book an appointment !) If you insist on doing it yourself, at least follow some guidelines.

Do Some Research

YouTube tutorials are hit or miss, but there’s a lot of good information out there from actual stylists. Just know that many stylists don’t even cut their own hair, so it’s not as easy as you might think. When I finally went to a salon to fix my botched cut, the stylists were perplexed at how I even got the scissors behind my head. If you’re going to do this thing, you want a couple of different mirrors so you can see your hair from every angle. In fact, here’s what you’ll need:

  • A decent pair of hair styling scissors (as opposed to, say, kitchen scissors)
  • At least two mirrors
  • A handful of hair ties
  • Newspaper or something else you can lay down to make cleanup easy

Know that there will be some trial and error. You’ll cut your hair evenly, it will look fine, you’ll move around and look at the back again, and suddenly, it’s all weird. Consider this when you schedule a time to chop. It will probably take longer than you think. Not only that, you’ll probably end up cutting off more than you think, so start longer than you planned, then work your way up.

Have a Backup Plan

Be prepared for the likely scenario that your new haircut will look like a toddler hacked it with safety scissors. You may just choose to grow it out, but you may hate your new cut so much that you want to take it to a salon and get it fixed like I did. If that’s the plan, make sure you’ve budgeted for it and you have time to do that in the first place.

Don’t Forget to Donate

Finally, don’t skip donating it . There are a handful of charities that collect hair for wigs. For example, Pantene and the American Cancer Society donate wigs to women with cancer and Locks of Love gives wigs to children with long-term hair loss. You can also ask your local salon for recommendations.

All the Body Parts You Can Donate to a Good Cause

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Most organizations want the hair to be between 8-10 inches long, and typically, they want you to braid or tie your hair in a rubber band before you cut and from there, you’ll mail your donation. Some organizations have requirements about whether the hair has been dyed, so check the charity’s requirements. If you’re going to impulsively and cathartically chop off your own hair, you might as well make it an even more gratifying experience by doing some good while you’re at it.


How fast hair grows, and other hairy science

On average, your scalp hair gro ws 0. 35 to 0.45 millimeters a day — that’s half an inch per month. Depending on your ancestry (genetics), diet and hormonal state (pregnant women grow hair a bit faster it’s also thicker and shinier), your hair will grow at a higher or lower rate.

Why hair grows

The human body contains roughly 5,000,000 hair follicles, and the function of each hair follicle is to produce a hair shaft. Our early ancestors used to have most of their bodies covered in hair, like our other primate cousins. This served to conserve heat, protect from the sun, provide camouflage and more. Today, however, humans stand out from t he 5,000 mammal species because they’re virtually naked, but why is that?

Scientists believe that our lineage has become less and less hairy in the past six million years since we shared a common ancestor with our closest relative, the chimpanzee. Our ape ancestors spent most of their time in cool forests, but a furry, upright hominid walking around in the sun would have overheated. One of the main theories concerning our lack of fur suggests that temperature control played a key role. Bare skin allows body heat to be lost through sweating, which would have been important when early humans started to walk on two legs and began to develop larger brains than their ape-like ancestors. Nina Jablonski, a professor of anthropology at Pennsylvania State University, says there must have been a strong evolutionary pressure to control temperature to preserve the functions of a big brain. “We can now make a very good case that this was the primary reason for our loss of hair well over 1 million years ago,” she said.

“Probably the most tenable hypothesis is that we lost most of our body hair as an adaptation to being better at losing heat from our body, in other words for thermal regulation,” Professor Jablonski said.

“We became very good sweaters as a result. We lost most of our hair and increased the number of eccrine sweat glands on our body and became prodigiously good sweaters,” she told the American Association for the Advancement of Science meeting in Boston.

Besides sweating, losing our furry coat may have also been driven by having fewer parasites infesting our bodies like ticks, lice, biting flies and other “ectoparasites.” These creatures can carry viral, bacterial and protozoan-based diseases such as malaria, sleeping sickness and the like, resulting in serious chronic medical conditions and even death. By virtue of being able to build fires and clothing, humans were able to reduce the number of parasites they were carrying without suffering from the cold at night or in colder climates.

Despite exposing us to head lice, humans probably retained head hair for protection from the sun and to provide warmth when the air is cold, while pubes may have been retained for they role in enhancing pheromones or the airborne odors of sexual attraction. The hair on the armpits and groin act like dry lubricants, allowing our arms and legs to move without chafing. Eyelashes, on the other hand, act as the first line of defense against bugs, dust, and other irritating objects. Everything else seems to be superfluous and was discarded. It’s important to note, however, that we haven’t exactly shed our fur. Humans have the same density of hair follicles on our skin as a similarly sized ape. Just look at your hands or fe et: they’re covered in hair, but the hair is so thin you can barely make them out.

How hair grows

Hair, on the scalp and elsewhere, grows from tiny pockets in the skin called follicles. Hair starts growing from the bottom of the follicles called the root, which is made up of cell proteins. These proteins are fed by blood vessels that dot the scalp. As more cells are generated, hair starts to grow in length through the skin, passing an oil gland along the way. Emerging from the pit of each of these follicles is the hair shaft itself. By the time it’s long enough to poke out through the skin, the hair is already dead, which is why you can’t feel anything when you get your hair cut.

The hair shaft is made out of a hard protein called keratin. There are three main layers to the hair shaft. The inner layer is called the medulla, the second is the cortex and the outer layer is the cuticle. It is both the cortex and the medulla that holds the hair’s pigment, giving it its color.

Some quick facts about hair:

  • You’re born with all the hair follicles you’ll ever have – about 5 million of them. Around 100,000 of these are on your scalp.
  • The hair on your head grows about 6 inches a year. The only thing in the human body that grows faster is bone marrow.
  • Males grow hair faster than females due to testosterone.
  • You lose between 50 to 100 strands of hair each day. That’s because follicles grow hair for years at a time but then take a break. Because follicle growth isn’t synced evenly, some take a break (causing the hair to fall out), while the vast majority continue business as usual.
  • Some follicles stop growing as you age, which is why old people have thinning hair or grow bald.
  • Everybody’s hair is different. Depending on its texture, your hair may be straight, wavy, curly, or kinky thick or thin fine or coarse. These are determined by genetics, which influences follicle shape. For instance, oval-shaped follicles make hair grow curly while round follicles groom straight hair.
  • Like skin, hair comes in various colors as determined by the same pigment called melanin. The more melanin in your hair, the darker it will be. As you grow older, your hair has less and less melanin, which is why it fades color and may appear gray.

Hair growth cycle

Follicles have three phases: anagen — growth, catagen — no growth, preparing for rest, and telogen — rest, hair falls out . At its own pace, each strand of hair on your scalp transitions through these three phases:

  • Anagen. During this phase, cells inside the root start dividing like crazy. A new hair is formed that pushes out old hair that stopped growing or that is no longer in the anagen phase. During this phase, the hair grows about 1 cm every 28 days. Scalp hair stays in this active form of growth for two to six years, but the hair on the arms, legs, eyelashes, and eyebrows have a very short active growth phase of about 30 to 45 days. This is why they are so much shorter than scalp hair. Furthermore, different people, thanks mostly to their genetics, have differing lengths of the anagen period for a given body part compared to other people. For the hair on your head, the average length of the anagen phase is about 2-7 years.
  • Catagen. About 3% of all the hair on your body this very instant is in this phase. It lasts two to three weeks and during this time, growth stops. During this phase, the hair follicle will actually shrink to 1/6 of its original length.
  • Telogen. About 6 to 8 percent of all your hair is in this phase — the resting phase. Pulling out a hair in this phase will reveal a solid, hard, dry, white material at the root. On a day-to-day basis, one can expect to shed between 100 to 150 pieces of hair. This is a normal result of the hair growth cycle. When you shed hair, it’s actually a sign of a healthy scalp. It’s when the hair loss is excessive that you should feel worried and contact a doctor.

Why hair only grows to a certain length

Each hair grows out of a follicle and as the hair gets longer and heavi er, the follicle eventually can’t hold on much longer and it sheds the hair. But that’s okay: it then starts growing another one. How long you can grow your hair depends on your genetics, and in general, Asians can grow their hair longer than Europeans. This may be surprising for many, but as in all mammals, each of us has a certain hair length beyond which the hair simply won’t grow. Hair length is longest in people with round follicles because round follicles seem to grip the hair better. So, people with straight hair have the potential to grow it longer. Shorter hair is associated with flat follicles. A study published in 2007 also explains why Japanese and Chinese people have thick hair: their follicles are 30% larger than that of Africans and 50% larger than that of Europeans.

In most cultures, women keep their hair longer than men. Cultural rules aside, hair length is actually sexual dimorphic. Generally, women are able to grow their hair longer than males. European males can reach a maximum length of wavy hair to about shoulder length, w hile the maximum for straight hair is about mid-back length. For European females, wavy hair can usually reach the waist, and straight hair can reach the buttocks or longer.

The world’s longest documented hair belongs to Xie Qiuping (China) at 5.627 m (18 ft 5.54 in) measured on 8 May 2004.

How to grow your hair faster and longer

While genetics caps your hair length, it is possible to accelerate its growth rate.

1. First of all, your hair growth reflects your general body health. Eat a diet rich in marine proteins, vitamin C (red peppers), zinc (oysters), biotin (eggs), niacin (tuna) and iron (oysters) to nourish strands.
2. If changing your diet isn’t possible, you can try supplements with marine extracts, vitamins, and minerals that nourish your follicles.
3. Besides general health, the next thing you should mind is your scalp health. Use a shampoo that gently exfoliates oil and debris from the scalp as well as a conditioner to moisturize scalp and hair.
4. Trimming is a proven method to grow your hair longer. Although in itself tri mming doesn’t promote growth, it does help prevent breakage an d, therefore, increases hair length.

Things that actually hurt your hair:

1. Silicone shampoos dry out the hair and degrade it. Blow dryers and flat iron produce similar effects, breaking the hair shafts. Use these products as rarely as possible.
2. UV light bleaches and breaks down hair. When you’re out at the beach, wear a hat to protect your scalp.
3. Salt and chlorine water both soften and dry the hair.
4. Bleaching, dyeing, hair extensions and perms also damage hair.


We took control of our own hair stories.

We started Nutrafol to help others do the same.

"After going the prescription route, I knew there had to be a better way. So we decided to find it."

*According to IQVIA ProVoice survey for 6 months ending March 31, 2021.

1 Ablon, G. J Drugs Dermatology, 2018. 2 Data on file, 2020. 3 Data on file, 2020. 4 Data on file, 2020.

BETTER HAIR IS JUST THE BEGINNING. LET’S KEEP GROWING.

Our own experience with thinning hair is what sparked our passion for hair wellness innovation. We strive to advance the field of hair science so you can be free to grow into the best version of yourself — your hair, your health, your happiness, and your power to help others grow too.

OUR PATENT

Synergen Complex ® is a registered patent of Nutraceutical Wellness Inc, US Patent #10,709,659 and 10,688,037.

© 2021 Nutraceutical Wellness Inc. All Rights Reserved.

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.

BETTER HAIR IS JUST THE BEGINNING. LET’S KEEP GROWING.

Our own experience with thinning hair is what sparked our passion for hair wellness innovation. We strive to advance the field of hair science so you can be free to grow into the best version of yourself — your hair, your health, your happiness, and your power to help others grow too.

OUR PATENT

Synergen Complex ® is a registered patent of Nutraceutical Wellness Inc, US Patent #10,709,659 and 10,688,037.