13 Fundamental Facts About the Anus

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The human body is an amazing thing. For each one of us, it's the most intimate object we know. And yet most of us don't know enough about it: its features, functions, quirks, and mysteries. Our series The Body explores human anatomy, part by part. Think of it as a mini digital encyclopedia with a dose of wow.

The anus might be the most underappreciated part of the body. Its very mention generally causes people to giggle or cringe. Yet without it, you'd be unable to eliminate waste and eventually die. In case your childhood wasn't enough to give you an accurate idea of its location, the anus is essentially the valve that stands between your poop and the toilet. It's considered the last piece of your digestive tract, essentially a two-inch long canal comprised of pelvic floor muscles and sphincters, easy to locate below either your vagina or your scrotum.

1. IT HAS TWO SPHINCTERS …

You may have heard talk of your "anal sphincter," which is not just one, but two valves. The internal sphincter is involuntary, meaning you can't squeeze it open—it's always closed up tight until it's time to poop. You can consciously hold closed the external, voluntary sphincter if you have to go to the bathroom but there's no toilet in sight, and consciously choose to open it when you're ready to poop. Thanks to your pelvic floor muscle, your poop normally doesn't come out when you don't want it to.

2. …AND ONE VERY IMPORTANT ROLE.

"The most important role is to eliminate waste," Rafael Lugo, a colorectal surgeon in Houston, tells Mental Floss. "We don't think much of it, but it's very important because if we don't eliminate waste, we have a [serious] problem." In rare cases, long-term constipation can cause illness and even death.

3. YOU REALLY SHOULD TAKE A LOOK AT IT … FOR YOUR HEALTH.

Since some of the health conditions of the anus don't cause any immediate symptoms you can feel, Lugo recommends you get comfortable looking at your anus from time to time. "We have these taboos in this society about looking at our bodies. Your body is your body. Touch it. The best place is in the shower. You have soap, feel the area. If anything is abnormal, take it to a mirror," he says. Once a year, have a professional look at it. He says he finds a lot of abnormalities that people live with and don't even know can be treated, such as fissures, hemorrhoids, and even cancer.

4. A SELF-CHECK CAN CATCH ANAL CANCER IN ITS EARLY STAGES.

"We can't control how [anal] melanoma happens, but it can be addressed early if you keep an eye on your butt. You can detect these changes early on and not die from it," Lugo advises. He recommends you "know your body head to toe. People tend to notice the dent in their car more often than they notice an issue in their body."

5. YOU DON'T HAVE TO SUNTAN TO GET ANAL CANCER.

Anal carcinoma, unfortunately, is not something you can usually feel with your hand. "It doesn't grow a tumor like a melanoma," Lugo says. "There's no bump." This kind of cancer can be genetic and is further reason to see a proctologist once a year, particularly if you have a family history of cancer.

6. ANAL SEX SLIGHTLY INCREASES YOUR RISK OF CANCER FROM THE HPV VIRUS.

Another form of anal carcinoma is caused by the human papilloma virus (HPV) that causes genital warts. While this virus can spread from a penis or vagina to an anus, chances of transmission are greater by anal sex. Unlike the convenient test for the HPV virus in the vagina, there's not a similar test for signs of HPV of the anus. This is another reason why having a professional look at your anus is a good idea. "There might be a little wart, something that looks abnormal. If you're sexually active, have multiple partners, or having high-risk sex, you should be more vigilant every few months," Lugo says.

7. THERE'S NOTHING DIRTY ABOUT THE ANUS.

So long as you handle your basic hygiene, your anus isn't dirty, Lugo insists. He says the anus doesn't require soap to stay clean, just water and wiping. In fact, soaps and shampoos can irritate and dry out the sensitive skin of the anus, so go easy on those. "It's a very complex organ that we basically disregard," says Lugo.

8. HUMANS HAVE WIPED THEIR BUTTS IN A LOT OF WAYS.

Over the centuries, before the advent of toilet paper, humans turned to a wide variety of objects with which to wipe their butts, including "leaves, grass, stones, corn cobs, animal furs, sticks, snow, seashells, and, lastly, hands," as Scientific American reported. Notice that most of these objects are hard, and you might really appreciate that squeezably soft Charmin.

9. BUTT HAIR IS NORMAL.

In your infrequent inspection of your anus, you may discover that hair grows down there. Scientists aren't entirely sure why. That hasn't stopped us laypeople from asking, though. In fact, so many SciShow viewers asked host Hank Green to tackle the subject that he dedicated an episode to it. The prevailing theories can be summed up as: 1. we simply haven't evolved away from hair there, because it doesn't get in the way of elimination or procreation; 2. it helps conduct scents that our ancient selves relied upon for reproductive purposes; or 3. it helps prevent irritation or chafing in that sensitive tissue.

10. HEMORRHOIDS ARE VARICOSE VEINS OF THE ANUS.

The veins in your anus "help the anus seal," like a closing door, says Lugo. But when you get a hemorrhoid, essentially just a swollen, dilated vein, "it's like having a shoe in the door, because there's something uneven there." Not only can hemorrhoids bleed, throb and itch, they can lead to a condition called anal seepage. "There are many modalities to take care of them, but they're not very comfortable, and you may need a surgery to take care of it," Lugo says.

11. IT IS POSSIBLE TO PREVENT HEMORRHOIDS.

The key to preventing hemorrhoids is avoiding constipation and straining on the toilet. "Prevention is important: Keep your stool soft, [take] plenty of fiber, and drink plenty of water," Lugo advises.

12. TRY NOT TO SIT ON THE TOILET FOR MORE THAN FIVE MINUTES.

Don't spend more than five minutes on the toilet, Lugo advises. "You shouldn't be sitting there having a social event." When you sit on the toilet seat, gravity exerts its pull on tissues, including hemorrhoids. "When your butt is hanging there, all the blood [flows] into there. Hemorrhoids are like balloons, they stretch and contract."

13. BURNING SENSATION? IT MAY NOT BE WHAT YOU THINK.

A burning or hot sensation of the anus is not always a hemorrhoid. It could be an anal fissure, or a tiny tear in the lining of the anus. "This can happen after a large bowel movement, especially if you already suffer constipation, which can stretch the anus," Lugo says. These can be treated by sitting in a hot bath for 20 minutes a day until the tissue heals. In cases where the fissure recurs and won't go away, surgery may be necessary.

10 Smart Facts About Your Gut

Colorized scanning electron micrograph of E. coli, a common gut bacteria
Colorized scanning electron micrograph of E. coli, a common gut bacteria
National Institute of Allergy and Infectious Diseases, Flickr // CC BY 2.0

Gut feelings get all the press, but your gut may be more of a thinker than you know. Some scientists now consider it a second brain. While it won’t necessarily help you study for an exam or get a promotion, your gut can influence the chemistry of your mood, emotions, immune system, and long-term health. Research even suggests the gut can “learn” new tricks through conditioning. These powerful connections are part an emerging field of science called neurogastroenterology designed to study the gut-brain link. Here are 10 facts you may not know about your gut.

1. THE GUT DOESN'T NEED THE BRAIN'S INPUT. 

You might think of your gut as a rebel against authority. It doesn’t wait for your brain’s impulses to do the important work of digestion, because it doesn’t need to—it acts as its own “brain.” No other organ, not even the all-powerful heart, can pull that off.

2. THERE ARE MORE THAN 100 MILLION BRAIN CELLS IN YOUR GUT.

Your gut’s power to think for itself is no surprise; there are millions of neurons in its lengthy coils (9 meters of intestines, from esophagus to anus). That’s more neurons than are found in the spinal cord or peripheral nervous system.

3. YOUR GUT HAS ITS OWN NERVOUS SYSTEM.

The enteric nervous system—the controlling mechanism of digestion and elimination—is the overlord of your gut, and functions all on its own. Some scientists see it as part of the central nervous system, while others consider it its own entity. It likely evolved to give the gut the go-ahead when the “got to go” impulse strikes, without requiring the brain’s sign-off, particularly when you consider the helplessness of an infant with its brand-new brain.

4. THERE'S AN INFORMATION HIGHWAY FROM YOUR GUT TO YOUR BRAIN.

There’s one big visceral nerve embedded in your gut—the vagus nerve. Research has revealed that up to 90 percent of its fibers carry information from the gut to the brain, rather than the other way around. In other words, the brain interprets gut signals as emotions. So you really should trust your gut.

5. MOST OF YOUR SEROTONIN IS IN YOUR GUT.

Some 95 percent of your body’s serotonin, that marvelous mood molecule that antidepressant drugs like Prozac keep in your body, can be found in the gut. So, it’s no wonder that diet, medications, and antibiotics can wreak havoc on one’s mood.

6. A HEALTHY GUT MAY PROTECT YOUR BONES.

In a study of the serotonin-gut relationship, scientists discovered an unexpected link between the gut and the bones. Inhibiting the gut’s release of serotonin counteracted the bone-density reduction of osteoporosis in mice. This research is going into studies on new osteoporosis-fighting drugs.

7. RESEARCH SHOWS LINKS BETWEEN AUTISM AND HAVING FEWER STRAINS OF GUT BACTERIA. 

In as many as nine out of 10 cases, autistic people have common gut imbalances such as leaky gut syndrome, irritable bowel syndrome, and fewer strains of “good” bacteria. Research on mice is looking at possible treatments of some of the behavioral disorders of autism by balancing microbes in the guts, though many warn that such treatments can’t produce a “cure” for autism.

8. FOOD REALLY DOES AFFECT YOUR MOOD. 

Different foods, when introduced to the gut via feeding tubes, have been shown to change a person's moods without the person’s awareness of what they were "eating." Fat, for instance, increased feelings of happiness and pleasure (no surprise there) because appeared to trigger the release of dopamine—the brain’s natural opiate. Carbohydrate consumption stimulated the release of serotonin, the “feel good” neurotransmitter.

9. YOUR GUT IS YOUR BEST FRIEND IN COLD AND FLU SEASON.

Not only does your gut hold brain cells, it also houses the bulk of your immune cells—70 percent—in the form of gut associated lymphoid tissue, or GALT, which plays a huge part in killing and expelling pathogens. GALT and your gut microbiome—the trillions of bacteria that live, like an immense microbial universe, in your gut—work hard to help you get over what ails you. That’s all the more reason to be careful with the use of antibiotics, which wipe out the good bacteria along with the bad.

10. YOUR GUT CAN BECOME ADDICTED TO OPIATES.

Inside your gut are opiate receptors, which are also found in the brain. The gut is just as susceptible to addiction as the brain and may contribute to the intense difficulty some addicts have trying to kick the habit.

What Causes Hiccups?

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iStock/damircudic

The cause of hiccups depends on whom you ask. The ancient Greek physician Galen thought hiccups were violent emotions erupting from the body, while others thought they were a sign of liver inflammation. Today, evidence points to spasms in the diaphragm, the large muscle between the chest and abdomen that aids airflow during breathing. This involuntary contraction can be brought on by a number of things that might irritate the nerves that control the movement of the muscle. A full stomach, heavy boozing, rapid shifts in temperature either inside or outside of the stomach, and certain emotions like shock or excitement are all common culprits.

No matter the cause, the result is the same: The diaphragm spasms and causes us to take a quick breath. The sudden rush of air causes the epiglottis (the flap that protects the space between the vocal cords) to shut and interrupt the breath, which makes the familiar "hic" sound.

WHAT CURES THEM?

The best cure for hiccups also depends on the person you ask. Almost all cures are based on one of two principles: One type works its magic by overwhelming the vagus nerve with another sensation. The vagus nerve is a cranial nerve that innervates the stomach and conveys sensory information about the body's organs to the brain. When distracted by overwhelming information of another sort, it basically tells the brain that something more important has come up and the hiccuping should probably be stopped (vagus nerve stimulation is also used to control seizures in epileptics and treat drug-resistant cases of clinical depression). The other method for curing hiccups is to interfere with the breathing, increasing the amount of carbon dioxide in the blood, and causing the body to focus on getting rid of the of the CO2 and not making hiccups.

Swallowing a spoonful of sugar is probably the most commonly prescribed hiccup cure and falls into the first category. A teaspoon of sugar is usually enough to stimulate the vagus nerve and make the body forget all about the hiccups. Even ardent supporters of the sugar cure disagree if the sugar should be taken dry or washed down with water, though.

If this home remedy doesn't work, and your hiccups are both severe and persistent, you may need to bring out the big guns. For chronic cases like this, doctors sometimes use a cocktail of Reglan (a gastrointestinal stimulant) and Thorazine (an anti-psychotic with sedative properties) to quiet things down. In some cases that resist these drugs, Kemstro, an anti-spasmodic, is also used. Other doctors have used vagus nerve stimulators implanted in the upper chest of patients. The pacemaker-like devices send rhythmic bursts of electricity through the vagus nerve to the brain to keep the hiccup cycle in check.

Many people prefer home remedies to battle their hiccups, which may include holding your breath, gargling ice water, or breathing into a paper bag. While the same people will swear by the treatment they've been using all these years, there's no firm scientific consensus that any of them actually work. But if it helps you, isn't that all that matters?

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

An earlier version of this article appeared in 2012.

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