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If you've ever dyed your hair the colors of the rainbow, or gotten a dramatic updo for a special event, you know that we often use hair for more than just keeping our heads warm. It can be an expression of our personalities, too.

But how your hair grows — or doesn't — can also be a sign about your personal health. And while that's really convenient and everything, it's also… pretty weird. Like, your hair is basically just a bunch of protein clumps, so it doesn't seem like it should be able to tell you about other things happening in your body.

But in reality, it's affected by all kinds of systems. So from dandruff to hair loss, here are five hair symptoms that can tell you about your health. In most cases, dandruff isn't anything to worry about.

It's often caused by a dry scalp, and can be fixed with special shampoos. But it's still worth paying attention to, because some kinds of dandruff can be a signal that something else is going on. For example, one of the main symptoms of a condition called seborrheic dermatitis is large, greasy, sometimes yellow dandruff flakes.

It also typically includes scaly patches on the scalp and redness on the skin, and in infants, it's often called cradle cap. This condition can impact other areas on the body, but it's often focused on the scalp because of all the sebaceous glands found there. These are openings in the skin that produce an oily substance, sebum, that naturally moisturizes skin and hair.

This type of dermatitis can happen to people of all ages, and to be clear, it's not caused by poor personal hygiene — or allergies. Many factors seem to work together to cause it, including naturally-occurring yeast found on the skin, called Malassezia. This yeast normally just feeds on sebum and minds its own business, but researchers suspect it can also cause problems.

They're still debating exactly how it does this, but it might be that an excess amount of yeast triggers a response from the immune system. Or maybe someone just has a general imbalance of microbes on their scalp. Regardless, it can be an itchy and sometimes uncomfortable experience, and doctors usually have a way to treat it — like by prescribing an antifungal medication.

So if your scalp begins shedding, maybe listen to what it has to say. There's nothing embarrassing about dandruff, people. Often, if you notice something troubling about your hair — besides whether or not you're having a bad hair day — it has to do with losing or gaining it in ways you wouldn't expect.

That's because, generally speaking, hair grows on a fairly predictable cycle with three main phases. First, there's the anagen phase, where your scalp hair is growing about a centimeter every month. Then, there's the catagen phase, where growth is beginning to stop, and finally, the telogen phase, where activity in your hair follicles has completely halted.

Like with dandruff, hair loss is often totally normal. The average person loses around 100 hairs a day just thanks to that normal growth cycle and there are plenty of common genetic reasons to start developing a bald spot or thinning hair. But if a lot of it starts falling out pretty suddenly that could be a sign of something more significant.

For example, if you frequently wear your hair in tight ponytails or braids, you might notice hair falling out due to a condition called traction alopecia. It's a gradual hair loss that's caused by pulling on your hair follicles too often, but if it's caught early, it's pretty easy to fix by switching to a looser hairstyle. There are also more surprising reasons hair can start to fall out, though — like a disorder called telogen effluvium, where hair prematurely shifts into the telogen phase.

This causes it to rapidly fall out, sometimes by the handful. It can be triggered by all kinds of factors, from severe illness to medication to plain old psychological stress. But generally, it happens because when the body is under stress it adjusts the amounts of hormones and chemicals it releases.

For example, if someone has a fever, their symptoms are caused by cytokine molecules. They're responsible for telling the body to raise its temperature in order to fight off sickness. But as a side effect, those cytokines can also tell the cells in hair follicles to die, causing an early telogen phase.

Even though that has nothing to do with a fever. These various changes are designed to help the body deal with whatever situation it's in, but they can also come with consequences. Thankfully, this shedding usually decreases over time, once the primary stressor has been resolved.

And in most cases, the hair grows back normally. Now, there are also a few conditions that cause especially unusual hair loss — like in weird patterns, or unusually smooth spots. Like, in up to 7% of cases, the secondary stage of syphilis can cause a unique baldness pattern that kind of looks like a moth-eaten sweater — although doctors are still trying to understand why.

There's also a condition called alopecia areata, which creates smooth, semi-round bald patches. Although they're most notable on the scalp, they can happen anywhere on the body. And they can happen suddenly, too, developing over the course of only a few days, which makes them different from your typical bald spot.

This time, though, it isn't mainly because of stress. Alopecia areata is thought to be an autoimmune disorder, and happens when the body attacks its own hair follicles. Normally, your immune system protects you against things like viruses and bacteria.

But sometimes, it will mistake healthy cells for invaders, and that's when an autoimmune disorder develops. In the case of alopecia areata, researchers think that a type of white blood cell called. T cells are sent to attack hair follicles based on what they've seen in experiments with mice.

They're still pinning down the details but it's possible that an imbalance between types of T cells could cause the attack. In some cases, scientists have noticed that patients with this condition have too many helper T cells which trigger immune system responses, and not enough regulatory ones. Still, regardless of what causes the attack it ultimately leads to the body producing signaling molecules that tell hair to fall out.

Researchers suspect that the odds of developing this condition might have to do with someone's genetic makeup since people with a family history of other autoimmune disorders seem to have a higher risk of developing it. And for those genetically predisposed to the disease various environmental factors that cause stress on the body may trigger alopecia areata to occur. Now, on the other side of the spectrum, you might sometimes notice extra hair growing where it didn't before.

This can be caused by multiple things that are usually pretty easy to identify depending on factors like your age and sex. For example, menopause causes someone's estrogen levels to drop which can lead to an excess of testosterone. And that can cause more hair to grow in unusual spots, or the hair to come in thicker or darker.

Alternatively, it could just be a random mutation. If you find a sudden dark hair somewhere you didn't expect, it might be because the hair cells mutated during growth. There are some conditions, though, that cause different types of hair to grow on your body.

One is called acquired hypertrichosis lanuginosa. It's a long a name that basically means fine, unpigmented hair — called lanugo hair — just starts showing up in various spots. Normally, you don't see lanugo hair much.

Its main job is to protect a fetus during development and it's typically shed before someone is born. But sometimes, it can regrow later in life in response to major changes happening in the body. This condition is sometimes associated with lymphoma or other various cancers but it's more frequently known as a symptom of anorexia nervosa.

Those with the disorder might see these fine hairs appear on their limbs, stomach, or back. It's possible that the body starts growing it to keep warm in the absence of body fat. But other researchers have suggested it could be a consequence of decreased thyroid activity, which can also happen in anorexia patients.

Of course, like other hair symptoms, the presence of lanugo hair doesn't mean someone is dealing with any of these conditions. This kind of hair growth can also be a side effect of a wide range of drugs, from immunosuppressants to anti-seizure medication. Finally, besides excess hair growth, there are also a few reasons for hair to come in thicker.

A big one is pregnancy. Higher estrogen levels during pregnancy trigger hair to stay in the anagen phase for longer, which means someone ends up with thicker locks. It also explains why hair loss after giving birth is common, when those estrogen levels go down.

There's also another type of hair growth that can be triggered by everything from polycystic ovary syndrome to medication, and it's called hirsutism. Although it can happen in all sexes, it's most common in biosex females. It causes them to grow hair in what's typically considered a male growth pattern with thicker hair developing in areas like the chest, upper lip, and jawline.

This growth is the result of the conversion of fine vellus hairs — the peach-fuzz type hair all over someone's body — into coarse terminal hairs. And although it can be caused by multiple conditions or medicines it's broadly linked to an increase in androgens. These are hormones that play a part in traditionally male traits and reproductive activity.

Hirsutism can sometimes happen randomly, especially in those of Middle Eastern, Mediterranean, or South Asian descent. But if it's accompanied by other symptoms — like increased acne or voice changes — doctors might take a closer look to make sure it's not a sign of a more serious hormone imbalance. Speaking of doctors, you've probably noticed that it's impossible to diagnose health issues just by looking at your hair, because the symptoms are shared with such a wide range of causes.

That means that, while changes in your hair can give you a heads up that something might not be right, what you see in the bathroom mirror shouldn't be your final diagnosis. It's fascinating that so many different things throughout the body — from your immune system to your hormones — can affect something as simple as your hair. But if your hair is trying to tell you something, please don't diagnose yourself using the.

Internet. Instead, this is the reason actual doctors exist and you should go talk to them. Thanks for watching this episode of SciShow!

If you want to learn more about what your body can tell you about your health — including why you keep getting those weird lines on your fingernails — you can watch our episode about nails after this. [ outro ].