8 Of Your Embarrassing Body Questions, Answered With Science

We asked for the science questions you didn't want your name attached to, and now we’re answering them. This time: eye gunk, blackheads, and are ovaries really rolled up testicles?!

A while ago we asked for your (anonymous) embarrassing science questions.

First we answered some of the weirdest requests we had (from how birds pee to whether or not fish get thirsty). Now we're moving on to ~bodies~. All questions are pretty much as we received them.

1. "What actually are blackhead pimples?"

Blausen.com staff / Creative Commons / Via commons.wikimedia.org

Both blackheads and whiteheads are pores in your skin that have become clogged with sebum and dead skin (yum). The difference is whiteheads are trapped under the skin and blackheads are exposed to the air. That's actually how blackheads end up black – the melanin in sebum reacts with oxygen in the air and turns a dark colour, as you can see in the handy diagram above.

2. "Can you sneeze with your eyes open?"

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You can try. You close your eyes when you sneeze because of a reflex: When your brain sends the message to sneeze, part of it tells your eyes to shut. “It is certainly possible to keep your eyes open if you try while you are sneezing… but it requires working against the reflex,” Dr Rachel Vreeman told NBC News in 2013.

And you don't have to worry about your eyes popping out if you manage it. If they were going to pop out, they'd do it whether your eyes were open or not, according to Dr Robert Naclerio, a professor of surgery and section chief of otolaryngology at the University of Chicago Medicine. He told NBC News: "There is no way that keeping your eyelids closed can prevent [your eyes from popping out]. It's not like the muscles are strong enough." (You can decide whether or not that's a good thing...)

3. "My boyfriend keeps telling me girls had testicles at birth but they rolled up inside them and turned into ovaries... true or not true?"

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The only truth in this is that ovaries and testicles start life in the same way.

For a little while in the womb, an embryo's gonads are the same whether that embryo is male or female. It's a gene called SRY (found on the Y chromosome) that controls how other genes function and stops these gonads turning into ovaries, putting them on a path to becoming testicles instead.

As always it's not *quite* as simple as SRY being the only gene that can control this switch between ovaries and testes. For example, in experiments on mice, scientists have been able to turn adult ovaries into testes in just three weeks by silencing a different gene, FOXL2, that appears to do the opposite of SRY – it stops gonads becoming testes. (Read this post by Ed Yong for the full story.)

But still, maybe your boyfriend should get a new fun fact.

4. "What's the purpose of wisdom teeth?"

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Wisdom teeth are the last set of molars to erupt, but they're not actually any different from your other molars. So their purpose is just normal toothy stuff. They come through when you're between the ages of 17 and 25, the age at which you're (um, supposedly) getting wiser, which seems to be how they got their name.

If there's enough room in your mouth, everything will work out fine. If there isn't, you might have to get those wisdom teeth removed. Thankfully, you'll still get to keep whatever wisdom you gained in your early twenties. Use it well.

5. "Do you have blue blood in your body?"

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All those diagrams that showed arteries as red and veins as blue lied to you. Deoxygenated blood is a darker red than oxygenated blood, but calling it blue would be a bit of a stretch (there's an interesting discussion to be had about how the perception of colour plays into this, but we'll save that for another time). Think about it: If there were blue blood in your veins, it'd come out that way when you cut yourself, right?

Veins look blue, however, when you view them through your skin because of the different wavelengths different colours of light have (blue is shorter than red) and how far into your skin the blood vessels you're looking at are.

6. "Why can we grow back skin, nails, hair, and stuff but not limbs?"

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The simple answer is: Scientists don't really know.

In order to regenerate limbs we'd need to hang on to the embryonic stem cells we have in the womb. During development we're able to grow all the organs we need thanks to these cells – but when we're born we switch them out for adult stem cells instead. Adult stem cells help repair our bodies: growing new layers of skin, forming scar tissue, and making new blood cells, for example. But they can't grow entire new limbs.

Some animals, like salamanders, can regrow limbs. One explanation for our inability to do the same is that we're warm-blooded mammals, Enrique Amaya, a developmental biologist at the University of Manchester, told BBC Future. Humans can't hide away for weeks without eating in order to regenerate a new limb, so our bodies do the best they can as quickly as they can.

7. "What is the gunk from my eyes for?"

Henry Gray / Via en.wikipedia.org

It's not really for anything, it's just a byproduct of how your eyes work. Your have something called meibomian glands (named after German physician Heinrich Meibom, also known as tarsal glands) in your eyelids. The glands make something called meibum, an oil that coats your eye to help you blink and stop your tears evaporating.

Overnight, this oil combines with rheum, the name for watery discharge that comes out of your eyes (and also nose). Because you're not blinking and washing it away like you do when you're awake, it all collects in the corner of your eye and dries up, meaning you wake up with "sleep" in your eye.

8. "Why do some parts of our bodies grow more hair than others?"

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Hair develops in three phases: anagen, catagen, and telogen. Anagen is the growth phase, so the longer the hair stays in this phase the longer it will grow.

Head hair typically stays like this for between two and six years, but hair on other parts of your body doesn't (eyebrows are only in anagen phase for about 10 weeks). After the anagen phase, your hair is cut off from its blood supply and will eventually fall out when new hair grows in its place.

As for why you have all that long hair on your head...maybe sexual selection?

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Keep an eye out for more answers to your questions in upcoming posts!