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What’s the Difference Between Hair and Fur?

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The most common distinction between hair and fur that people tend to make is usually between you and your pet. You have hair on your head, and your dog Fido has fur all over its body. Easy enough, right?

Well, actually, it's kind of complicated. "The way I think a lot of people understand fur versus hair is in the density of follicles," says Ross McPhee, Curator of the Department of Mammalogy at the American Museum of Natural History. "So for fur-bearing animals—which were converted into coats and so-forth—people always wanted it to be something that was very dense, so there’s the idea therefore that fur is dense, and it certainly is in [the] kinds of fur-bearers that we use for this purpose. Whereas hair is not so dense. There's less of it." The reason this distinction doesn’t work, however, is that humans have a similar follicle density to any other ape, and an adult scalp has the same follicle density as a mouse

Chemically, it's all keratin—the same protein substance that also makes up skin, feathers, nails, hoofs, claws, and horns—that grows on mammals (either all over or just in certain places). So, MacPhee says, "fundamentally, they are all the same thing. Naturally, there’s specialization, just as there are in tissues all over the body."

There are three main types of hair: ground hair, guard hair, and whiskers. Two of them, ground and guard, are classified as fur. Ground hair is used primarily as insulation and is soft, while guard hair is for protection from the elements and tends to be coarse. Because it's in-between ground and guard, human hair can be reasonably called fur.

No matter how human hair is classified, however, the distinction between hair and fur shows up in the third category: whiskers.

Whiskers, although hair, are categorically not fur. Whiskers have a few differences, including that they tend to be longer and stiffer (but this is not always the case), and they're important sensory organs. "Every follicle has a certain amount of innervation," MacPhee explains. The way it works for whiskers is that they have mechanoreceptors, which means that when the whisker is disturbed by hitting an object, a signal is immediately sent back to the brain and analyzed there. Which is why whiskers are utilized by all kinds of mammals as a sensory apparatus in their environment. A manatee's face [PDF], for instance, is exclusively whiskers because every follicle has these key (and distinct) features. These types of whiskers are known as vibrissae—and humans don't have them. "The whiskers that you find on a male are just hair," MacPhee says. "They’re not richly endowed with these sensory nerves. Whether they’re on the muzzle, or the eyebrows, or on other places on the body. Very frequently, mammals have vibrissae on their wrists and ankles. Although cats and dogs have good vision, it’s clear they’ve retained vibrissae and some degree of information to fine tune their body."

Ultimately, though, it might just be a word thing. "I’m not sure that the hair versus fur distinction is always made in other languages," MacPhee says. "Humans universally only have hair, right? Not fur, even though there is no important way to distinguish the two. The differences are arbitrary."

THE GROWTH MYTH

“Wait a second!” you scream before you admit that you have fur on you. “I thought the common difference is that hair keeps growing while fur has a set length at which it stops!” That's not true: Human hair doesn’t keep growing and growing. All hair—whether it’s on your human head and arms or on the body of a chimpanzee or on beloved Fido—has a growth limit based on genetics, so your shorthaired cat will stay shorthaired even if you don’t get its fur trimmed.

The myth of the difference between hair and fur is perpetuated by a misunderstanding of the hair growth cycle in the body that regulates hair length. The “anagen” period of the cycle is the phase of constant hair growth; the “catagen” phase is a transitional time when the body tells the hair to begin to stop growing, shrinking the strands themselves and cutting the roots of the hairs so new strands won’t be produced; and the “telogen” phase is when the hair follicle rests and no new growth occurs. This leads to the “exogen” phase, in which the hair falls out to start the cycle over again.

So in humans, hair will stop growing after the cycle runs through each phase. It’s just that the cycle in you as a human is longer than, say, Fido’s hair growth cycle. The anagen period of active growth on a human scalp could run anywhere from 2 to 7 years (taking into consideration other factors such as baldness), while the telogen period in which the hair on your scalp is dormant could go up to 100 days.

The cycle itself is relative not only to different species, but also to different areas of the body, which explains why the hair on your arms and legs isn’t the same length as the hair on your head. For instance, the same 2- to 7-year anagen phase on your head lasts 30 to 45 days on your arms and legs.

On animals, the hair all seems to be a fixed length to us because their cycle is relatively shorter when compared to ours, and so the mistake of differentiating fur from hair is made. It becomes clearer when you consider that longer haired dogs just have a longer period of hair growth than something like a Lab, which has a shorter cycle.

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Big Questions
Why Do Fruitcakes Last So Long?
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Fruitcake is a shelf-stable food unlike any other. One Ohio family has kept the same fruitcake uneaten (except for periodic taste tests) since it was baked in 1878. In Antarctica, a century-old fruitcake discovered in artifacts left by explorer Robert Falcon Scott’s 1910 expedition remains “almost edible,” according to the researchers who found it. So what is it that makes fruitcake so freakishly hardy?

It comes down to the ingredients. Fruitcake is notoriously dense. Unlike almost any other cake, it’s packed chock-full of already-preserved foods, like dried and candied nuts and fruit. All those dry ingredients don’t give microorganisms enough moisture to reproduce, as Ben Chapman, a food safety specialist at North Carolina State University, explained in 2014. That keeps bacteria from developing on the cake.

Oh, and the booze helps. A good fruitcake involves plenty of alcohol to help it stay shelf-stable for years on end. Immediately after a fruitcake cools, most bakers will wrap it in a cheesecloth soaked in liquor and store it in an airtight container. This keeps mold and yeast from developing on the surface. It also keeps the cake deliciously moist.

In fact, fruitcakes aren’t just capable of surviving unspoiled for months on end; some people contend they’re better that way. Fruitcake fans swear by the aging process, letting their cakes sit for months or even years at a stretch. Like what happens to a wine with age, this allows the tannins in the fruit to mellow, according to the Wisconsin bakery Swiss Colony, which has been selling fruitcakes since the 1960s. As it ages, it becomes even more flavorful, bringing out complex notes that a young fruitcake (or wine) lacks.

If you want your fruitcake to age gracefully, you’ll have to give it a little more hooch every once in a while. If you’re keeping it on the counter in advance of a holiday feast a few weeks away, the King Arthur Flour Company recommends unwrapping it and brushing it with whatever alcohol you’ve chosen (brandy and rum are popular choices) every few days. This is called “feeding” the cake, and should happen every week or so.

The aging process is built into our traditions around fruitcakes. In Great Britain, one wedding tradition calls for the bride and groom to save the top tier of a three-tier fruitcake to eat until the christening of the couple’s first child—presumably at least a year later, if not more.

Though true fruitcake aficionados argue over exactly how long you should be marinating your fruitcake in the fridge, The Spruce says that “it's generally recommended that soaked fruitcake should be consumed within two years.” Which isn't to say that the cake couldn’t last longer, as our century-old Antarctic fruitcake proves. Honestly, it would probably taste OK if you let it sit in brandy for a few days.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Big Questions
What's the Difference Between Stuffing and Dressing?
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For carbohydrate consumers, nothing completes a Thanksgiving meal like stuffing—shovelfuls of bread, celery, mushrooms, and other ingredients that complement all of that turkey protein.

Some people don’t say “stuffing,” though. They say “dressing.” In these calamitous times, knowing how to properly refer to the giant glob of insulin-spiking bread seems necessary. So what's the difference?

Let’s dismiss one theory off the bat: Dressing and stuffing do not correlate with how the side dish is prepared. A turkey can be stuffed with dressing, and stuffing can be served in a casserole dish. Whether it’s ever seen the inside of a bird is irrelevant, and anyone who tells you otherwise is wrong and should be met with suspicion, if not outright derision.

The terms are actually separated due to regional dialects. “Dressing” seems to be the favored descriptor for southern states like Mississippi, Tennessee, South Carolina, and Georgia, while “stuffing” is preferred by Maine, New York, and other northern areas. (Some parts of Pennsylvania call it "filling," which is a bit too on the nose, but to each their own.)

If “stuffing” stemmed from the common practice of filling a turkey with carbs, why the division? According to The Huffington Post, it may have been because Southerners considered the word “stuffing” impolite, so never embraced it.

While you should experience no material difference in asking for stuffing or dressing, when visiting relatives it might be helpful to keep to their regionally-preferred word to avoid confusion. Enjoy stuffing yourselves.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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