If you’ve ever looked down at your belly button in wonder, you’re not alone. Navel gazing to contemplate the mysteries of the universe dates back to early Hinduism and ancient Greece. The Greek philosophers even gave this kind of meditative musing a name: Omphaloskepsis — omphalos (navel) and skepsis (to look at or examine). It’s hard to believe that mouthful didn't catch on, isn’t it?

Here are some more random facts about belly buttons, and a look at whether yours is “normal” or not.

What’s a belly button, anyway?

Your belly button is more than a great way to prove you're not a cyborg. Your belly button is actually your first scar. Within minutes of being born, your umbilical cord was clamped and cut, leaving a short umbilical stalk sticking out of your abdomen. It shriveled up, turned black, dried up, and fell off. (Who said babies aren't adorable?)

Innie or outie?

The Greeks pondered many existential questions, but there's no record that Socrates ever invited Plato to skepsis his omphalos and asked, "Does this look OK to you?"

So what is a "normal" belly button, anyway? The majority of people have "innies," the very scientific term for belly buttons that dip inward. Protruding "outies" can be found on approximately 10 percent of the population. They’re about as common as left-handedness.

A longstanding theory, or old wives' tale, "blames" doctors' techniques for creating outies. But there’s no proof that cutting the umbilical cord a certain way, or at a certain length, results in an outie. The more likely determining factor is the amount of space between your skin and your abdominal muscle wall, according to this plastic surgeon. That is, if you have room to nest an innie, you will. If you don't, you won't.

Pregnant women know that an innie can temporarily become an outie as their abdomens grow and their belly buttons pop out. All of this is normal.

That being said, innies do seem to be the more desirable belly button. Cosmetic surgery to turn an outie into an innie is common. (Innie into an outie, not so much.) Note: In case you were wondering, innie people don't live happier lives, make more money, or score better seats to Hamilton.

So when is a belly button not normal?

Umbilical hernia

If a baby's belly button suddenly protrudes when the baby laughs, it's not their little buddy popping up to see what's so funny. It can be an umbilical hernia. Umbilical hernias occur when the stomach wall fails to fully develop around the umbilical cord. The hernia bulges out when the baby cries, laughs, sneezes, poops, or otherwise exerts pressure on the abdomen. Most umbilical hernias heal on their own because babies are wonderfully resilient. But if they don't, a simple surgery can correct the problem.

Fecal or menstrual leakage

Yes, you read that right. It is possible for feces or menstrual blood to come out of a belly button. An umbilical fistula, an abnormally developed passageway between the intestines and the umbilicus, can cause fecal matter to leak from the navel. It goes without saying, if poop is coming out of your belly button, you should seek medical attention.

And just for the ladies, rare cases of endometriosis can cause some women to get their periods in their belly buttons. Do they make a tampon for that? No, no they don't.

Endometriosis is the abnormal growth of endometrium (uterine lining tissue) in places that are not the uterus. The tissue can end up in the bladder, liver, bowel, and other places. Whoever said women are more likely to ask for directions never met an endometrium.

No matter how lost it is, the endometrium can still hear the siren's call of menstrual hormones and will act accordingly. So, during the menstrual cycle, it will slough off cells as usual. And if those cells are within the umbilicus, the blood's only way out is through the belly button.

Fecal and menstrual leakages aren’t life-threatening, per se, but they're also not something to ignore. If you experience these issues, see your doctor.

Infections

Garden-variety belly button infections are nowhere near as cool as pooping or menstruating belly buttons. The most common causes of navel infections are piercings and plain ol’ poor hygiene.

Infection symptoms are what you’d expect: pain or tenderness, redness, and swelling, sometimes accompanied by discharge and a foul smell. For those of us who are proud of our innies, it comes with a price — the dark, warm environment is the perfect place for bacteria to grow, or for a yeast infection to move in. For more information about all the things that can go wrong with belly buttons and what to do about them, go here.

4 really weird belly button facts

You've probably never devoted this much time to thinking about belly buttons, so why stop now? Here are some truly strange facts to delight your friends at your next dinner party.

1. Your body might say "no way" to your new piercing

If you've ever horrified your mother by coming home with a navel piercing, be aware that it might not last. Some bodies see foreign objects as intruders and literally spit them out. When this happens, new cells start growing behind the piercing, slowly pushing it closer to the skin's surface, until one morning, you wake up and your cute belly ring is laying on your stomach. There’s nothing worse than having your own body agree with your mother!

2. Most belly button lint is blue

Why? Because jeans. Think about it. Also, blue is the most common clothing color. This is also why dryer lint is usually bluish.

3. Your belly button is an erogenous zone

Even though the belly button is just a scar, the area has many nerve endings, making it ticklish, sensitive, and — if you're like Madonna — a love button that shoots sex tingles up your spine. If it can be licked, dipped, sipped, or dripped, someone has put it into a belly button during sexy time. Is that someone you? You can tell us.

4. Some people don't have typical belly buttons

When inside the womb, certain developmental problems with the bladder, intestinal tract, and belly wall can a leave a person without a typical belly button. Often these individuals will choose plastic surgery when they’re older to reconstruct their belly button. Some people, like super model Karolina Kurkova, have what can only be described as in-betweenies. Due to her lack of an innie or outtie, her photos are sometimes retouched to create the look of a belly button.

Takeaway: All buttoned up

Unless your belly button is sick, injured, or pooping, it's completely normal. And anything you want to do with it is normal, too. If you have an outie, but want an innie, go for it. There is a surgery for that. No one can tell you what makes you happy. If you want to pierce it or tattoo it, terrific! Just be sure to keep it clean and dry.