10 Vital Facts About the Scrotum


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 scrotum may appear to be nothing more than a bit of baggy skin, but it serves some very important functions for human health and reproduction. The testicles, which produce sperm, would be unprotected and subject to the elements without the scrotum—so without it, none of us might exist. To learn more, Mental Floss spoke to Brian Levine, a reproductive endocrinologist and fertility specialist at the New York office of the Colorado Center for Reproductive Medicine. 


"The scrotum is a genius," Levine tells Mental Floss. While that may be a stretch, he says that the main purpose of the scrotum "is to hold the testicles outside of the body," which helps to keep the testicles cooler than body temperature. Because sperm are so sensitive to temperature fluctuations, this helps preserve their health.


"Increased body temperature or temperature in general [such as a hot tub] leads to chromosomal abnormalities. By keeping the temperature lower you protect the DNA being formed to put the sperm together from having inborn errors," Levine explains.


As the body gets colder, muscle fibers bring the scrotum closer to the body to regulate them. When the person is warmer, they will hang lower from the body. "The average person has one testicle higher than the other," Levine says. Size and shape variance of testicles is not in and of itself cause for concern—unless you experience a sudden change.


Also by keeping the testicles at a lower temperature, metabolically, Levine says, "you keep sperm swimming slower, so you end up preserving them."


A 2013 study [PDF] on birth control methods of an indigenous culture in Zimbabwe describes how men were instructed to expose their testicles to "above average heat from fire" in the belief that this would weaken the sperm. While there is a connection between temperature and sperm health, this is not a recommended practice for birth control as it is unlikely to successfully reduce the sperm count. In addition, the study notes, "testicles with too high of a body temperature are associated with testicular cancers," though others argue that the jury is still out on that purported connection. Either way, you should probably keep your scrotum away from open flame.

In a similar vein, Marthe Voegeli, a Swiss doctor and early pioneer in fertility in the 1950s, designed a study in which men sat in a shallow or testes-only bath of 116°F for 45 minutes daily for three weeks. Her study claimed that this resulted in between four and six months of infertility. Fertility returned to normal eventually, and children born of those men were healthy and normal. She took her method to India, to help families suffering from famine and poverty prevent further pregnancies. While she claimed her methods to be successful, most doctors today would not recommend this as a reliable contraceptive practice.


Even the scrotum is susceptible to cancer, Levine points out. "Wherever there's skin, you can get melanoma," he says. This can be a result of metastases of cancer that spread from somewhere else in the body, or, if you're a nude sunbather, be warned: "If you expose it to sunlight, you can get melanoma."


If you are male, not prepubescent, and don't have a scrotum, it may mean you have undescended testicles, Levine says, "which can end up leading to infertility." Most testicles will descend eventually, but sometimes they can be helped along by surgery.


Common issues of the scrotum that may require surgical intervention include varicoceles, which are essentially varicose veins in the scrotum that can cause infertility by pooling blood, which can effect sperm count and motility. Varicoceles can also cause testicles to fail to develop normally or shrink. A hydrocele, which doctors informally call "water on the testicle," Levine says, is simply a fluid-filled cyst that surrounds a testicle and causes swelling in the scrotum. Levine adds that since the scrotum allows for good evaluation of testicles, "If you feel any lumps, bumps or abnormalities, you should see a medical professional."


Should you need surgery for one of those conditions, or for a vasectomy, Levine reassures that modern day surgical techniques "mostly spare the scrotum and require a minimal, barely visible incision in the testicle." Weill Cornell Medical Center has even perfected what they call a no-scalpel vasectomy that uses specialized forceps instead.


In the late 1700s and early 1800s, chimney sweeps—who were often young boys because they were small enough to fit—would develop scrotal cancer from creosote collecting between the skin folds on the scrotum.

Sir Percival Pott, an English surgeon considered the father of orthopedics and the first to draw the connection between occupations and certain illnesses, also made the connection between chimney sweeps and scrotal cancer, writing: " … there is a different disease peculiar to a certain set of people, which has not, at least to my knowledge, been publicly noticed; I mean the chimney-sweeper's cancer. It is a disease which makes its first attack on, and appearance in, the inferior part of the scrotum; where it produces a superficial, painful, ragged, ill-looking sore, with hard and rising edges: the trade call it the soot-wart." (We know now that a chemical in soot caused genetic damage to chromosome 17.)

After this connection was made, physicians recommended that chimney sweeps change their clothes weekly and wash their genitals daily.   

Why Can You Sometimes See Your Breath?

Chalabala/iStock via Getty Images
Chalabala/iStock via Getty Images

The human body is made up of about 60 percent water, meaning that when we breathe, we don’t just exhale carbon dioxide—we also exhale a certain amount of water vapor.

Water molecules need a lot of energy in order to remain in a gaseous form. When the warm water vapor molecules from your lungs reach colder air, they condense into “tiny droplets of liquid water and ice,” according to Wonderopolis. In fact, this process of condensation is also how clouds are formed.

But it’s actually relative humidity, not just temperature, that determines whether you can see your breath. The water vapor in your breath condenses into a liquid when it hits dew point—the temperature at which the air is saturated and can’t hold any more water in gas form. Since cold air can’t hold as much water vapor as warm air, you're much more likely to see your breath on a chilly day, but that's not always the case.

On more humid days, you may be able to see your breath even when it’s relatively warm outside. That’s because the air is already more saturated, making the dew point higher. And on especially dry days, even if it's cold outside, you may not be able to see your breath at all. Dry, unsaturated air can hold more water vapor, so you can huff and puff without seeing any evidence of it at all.

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7 Facts About Blood

Moussa81/iStock via Getty Images
Moussa81/iStock via Getty Images

Everyone knows that when you get cut, you bleed—a result of the constant movement of blood through our bodies. But do you know all of the functions the circulatory system actually performs? Here are some surprising facts about human blood—and a few cringe-worthy theories that preceded the modern scientific understanding of this vital fluid.

1. Doctors still use bloodletting and leeches to treat diseases.

Ancient peoples knew the circulatory system was important to overall health. That may be one reason for bloodletting, the practice of cutting people to “cure” everything from cancer to infections to mental illness. For the better part of two millennia, it persisted as one of the most common medical procedures.

Hippocrates believed that illness was caused by an imbalance of four “humors”—blood, phlegm, black bile, and yellow bile. For centuries, doctors believed balance could be restored by removing excess blood, often by bloodletting or leeches. It didn’t always go so well. George Washington, for example, died soon after his physician treated a sore throat with bloodletting and a series of other agonizing procedures.

By the mid-19th century, bloodletting was on its way out, but it hasn’t completely disappeared. Bloodletting is an effective treatment for some rare conditions like hemochromatosis, a hereditary condition causing your body to absorb too much iron.

Leeches have also made a comeback in medicine. We now know that leech saliva contains substances with anti-inflammatory, antibiotic, and anesthetic properties. It also contains hirudin, an enzyme that prevents clotting. It lets more oxygenated blood into the wound, reducing swelling and helping to rebuild tiny blood vessels so that it can heal faster. That’s why leeches are still sometimes used in treating certain circulatory diseases, arthritis, and skin grafting, and helps reattach fingers and toes. (Contrary to popular belief, even the blood-sucking variety of leech is not all that interested in human blood.)

2. Scientists didn't understand how blood circulation worked until the 17th century.

William Harvey, an English physician, is generally credited with discovering and demonstrating the mechanics of circulation, though his work developed out of the cumulative body of research on the subject over centuries.

The prevailing theory in Harvey’s time was that the lungs, not the heart, moved blood through the body. In part by dissecting living animals and studying their still-beating hearts, Harvey was able to describe how the heart pumped blood through the body and how blood returned to the heart. He also showed how valves in veins helped control the flow of blood through the body. Harvey was ridiculed by many of his contemporaries, but his theories were ultimately vindicated.

3. Blood types were discovered in the early 20th century.

Austrian physician Karl Landsteiner discovered different blood groups in 1901, after he noticed that blood mixed from people with different types would clot. His subsequent research classified types A, B and O. (Later research identified an additional type, AB). Blood types are differentiated by the kinds of antigens—molecules that provoke an immune system reaction—that attach to red blood cells.

People with Type A blood have only A antigens attached to their red cells but have B antigens in their plasma. In those with Type B blood, the location of the antigens is reversed. Type O blood has neither A nor B antigens on red cells, but both are present in the plasma. And finally, Type AB has both A and B antigens on red cells but neither in plasma. But wait, there’s more! When a third antigen, called the Rh factor, is present, the blood type is classified as positive. When Rh factor is absent, the blood type is negative.

Scientists still don’t understand why humans have different blood types, but knowing yours is important: Some people have life-threatening reactions if they receive a blood type during a transfusion that doesn’t “mix” with their own. Before researchers developed reliable ways to detect blood types, that tended to turn out badly for people receiving an incompatible human (or animal!) blood transfusion.

4. Blood makes up about 8 percent of our total body weight.

Adult bodies contain about 5 liters (5.3 quarts) of blood. An exception is pregnant women, whose bodies can produce about 50 percent more blood to nourish a fetus.)

Plasma, the liquid portion of blood, accounts for about 3 liters. It carries red and white blood cells and platelets, which deliver oxygen to our cells, fight disease, and repair damaged vessels. These cells are joined by electrolytes, antibodies, vitamins, proteins, and other nutrients required to maintain all the other cells in the body.

5. A healthy red blood cell lasts for roughly 120 days.

Red blood cells contain an important protein called hemoglobin that delivers oxygen to all the other cells in our bodies. It also carries carbon dioxide from those cells back to the lungs.

Red blood cells are produced in bone marrow, but not everyone produces healthy ones. People with sickle cell anemia, a hereditary condition, develop malformed red blood cells that get stuck in blood vessels. These blood cells last about 10 to 20 days, which leads to a chronic shortage of red blood cells, often causing to pain, infection, and organ damage.

6. Blood might play a role in treating Alzheimer's disease.

In 2014, research led by Stanford University scientists found that injecting the plasma of young mice into older mice improved memory and learning. Their findings follow years of experiments in which scientists surgically joined the circulatory systems of old and young mice to test whether young blood could reverse signs of aging. Those results showed rejuvenating effects of a particular blood protein on the organs of older mice.

The Stanford team’s findings that young blood had positive effects on mouse memory and learning sparked intense interest in whether it could eventually lead to new treatments for Alzheimer’s disease and other age-related conditions.

7. The sight of blood can make people faint.

For 3 to 4 percent of people, squeamishness associated with blood, injury, or invasive medical procedures like injections rises to the level of a true phobia called blood injury injection phobia (BII). And most sufferers share a common reaction: fainting.

Most phobias cause an increase in heart rate and blood pressure, and often muscle tension, shakes, and sweating: part of the body’s sympathetic nervous system’s “fight or flight” response. But sufferers of BII experience an added symptom. After initially increasing, their blood pressure and heart rate will abruptly drop.

This reaction is caused by the vagus nerve, which works to keep a steady heart rate, among other things. But the vagus nerve sometimes overdoes it, pushing blood pressure and heart rate too low. (You may have experienced this phenomenon if you’ve ever felt faint while hungry, dehydrated, startled, or standing up too fast.) For people with BII, the vasovagal response can happen at the mere sight or suggestion of blood, needles, or bodily injury, making even a routine medical or dental checkup cause for dread and embarrassment.