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You asked: Why do I need a haircut?

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A reader named Brooks wanted to know: "Why does the hair on your head constantly grow while the hair on your body has a limit?"

Technically, the hair on your head has a limit too -- like all hair, it has a growth spurt followed by a dormant phase. Here's an explanation from, of all places, a website about dogs:

Anagen is a period of new hair growth. The longer the anagen period, the longer the hair grows. Human scalp hair may stay in anagen for 2-6 years. Human hair on arms and legs may stay in anagen for only 30-45 days. Catagen is a transition phase. During catagen growth stops and the outer root sheath shrinks attaching to the root of the hair. Telogen is the resting phase. For human scalp hair the resting phase is about 100 days. The telogen phase for human hair on arms and legs is much longer than for scalp hair. Exogen is when the hair falls out, and the follicle enters a new anagen period, growing a new strand of hair.

So, in other words, your head hair grows for a long time but doesn't stay put for more than a couple of months after it's done -- right now, probably about 90 percent of your head hairs are having a growth spurt -- whereas your leg hair grows just a little and then clings on stubbornly for months without falling out.

For a deeper, more evolutionary explanation -- and some ruminations on the difference between "hair" and "fur" -- check out Science Daily.

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Big Questions
What Is the Difference Between Generic and Name Brand Ibuprofen?
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What is the difference between generic ibuprofen vs. name brands?

Yali Friedman:

I just published a paper that answers this question: Are Generic Drugs Less Safe than their Branded Equivalents?

Here’s the tl;dr version:

Generic drugs are versions of drugs made by companies other than the company which originally developed the drug.

To gain FDA approval, a generic drug must:

  • Contain the same active ingredients as the innovator drug (inactive ingredients may vary)
  • Be identical in strength, dosage form, and route of administration
  • Have the same use indications
  • Be bioequivalent
  • Meet the same batch requirements for identity, strength, purity, and quality
  • Be manufactured under the same strict standards of FDA's good manufacturing practice regulations required for innovator products

I hope you found this answer useful. Feel free to reach out at www.thinkbiotech.com. For more on generic drugs, you can see our resources and whitepapers at Pharmaceutical strategic guidance and whitepapers

This post originally appeared on Quora. Click here to view.

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Big Questions
Do Cats Fart?
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Certain philosophical questions can invade even the most disciplined of minds. Do aliens exist? Can a soul ever be measured? Do cats fart?

While the latter may not have weighed heavily on some of history’s great brains, it’s certainly no less deserving of an answer. And in contrast to existential queries, there’s a pretty definitive response: Yes, they do. We just don’t really hear it.

According to veterinarians who have realized their job sometimes involves answering inane questions about animals passing gas, cats have all the biological hardware necessary for a fart: a gastrointestinal system and an anus. When excess air builds up as a result of gulping breaths or gut bacteria, a pungent cloud will be released from their rear ends. Smell a kitten’s butt sometime and you’ll walk away convinced that cats fart.

The discretion, or lack of audible farts, is probably due to the fact that cats don’t gulp their food like dogs do, leading to less air accumulating in their digestive tract.

So, yes, cats do fart. But they do it with the same grace and stealth they use to approach everything else. Think about that the next time you blame the dog.

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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