YOUR AMAZING BODY!

Your fingerprints can predict some health issues. Looking at the sun can make you sneeze. You grow a new skeleton every ten years. Science hasn’t uncovered every mystery, but what it has discovered will blow your mind.

What do fingerprints reveal about your health risks? How do your cells defend against cancer? Science has many of the answers—but not all.

Science Knows Why ...

1. You get goose bumps. When you feel a chill or see something scary, your body releases a surge of adrenaline. The point is to make your body hair stand up—which helped our animal ancestors stay warm and also made them look larger in the face of predators. Getting those individual hairs to stand at attention requires the teeny skin muscles at the base of each follicle to contract, making your skin look vaguely like a goose’s postplucking—hence, goose bumps.

2. You grow wisdom teeth. Wisdom teeth are actually a third set of molars. They allowed our forebearers to munch on rough food such as roots, nuts, and meat, especially when other teeth fell out (alas, our ancestors had poor oral hygiene). About 35 percent of people never develop wisdom teeth, partly because of an evolutionary shift that means the human jaw is often too small for them. The rest of us start developing them by age ten, though they don’t fully emerge until young adulthood, which is when we (allegedly) acquire full-grown wisdom.

3. Your fingers and toes wrinkle in

water. When you’re in the bath, water seeping into your skin makes the upper layers swell. That causes the blood vessels below to constrict, which in turn causes some of the upper layers of skin to collapse. The irregular pattern of swelling and falling skin is what we see as wrinkles on our fingertips and toes.

4. Your knees crack after sitting for

a long time. The sounds you hear are probably caused by gas being released from the spaces between your joints—just like when you crack your knuckles. Meanwhile, muscles or tendons rubbing against your bones may also make your joints creaky. “We say motion is lotion,” Kim L. Stearns, MD, an orthopedic surgeon at Lutheran

Hospital in Ohio, told the Cleveland Clinic. “When you’ve been sitting around, fluid in the joints doesn’t move. The more active you are, the more your joints lubricate themselves” and the less noise they will make. The popping shouldn’t alarm you unless it is accompanied by pain or swelling.

5. You get a stitch in your side from running.

Starting a new exercise routine can cause pressure to push up from the abdomen or down from the lungs onto the diaphragm muscle between them. This restricts blood flow and causes the irritated diaphragm to spasm. Once your body gets used to exertion, side stitches should cease.

6. Your stomach growls when you’re hungry.

When the receptors in the stomach walls sense an absence of food, they send out electrical waves. These cause the muscular walls of the stomach to squeeze and release, making a rumbling sound. You may also hear some sloshing as these contractions move water and stomach acid around.

7. Your saliva tastes metallic right before you vomit.

Saliva normally has a ph ranging from about six to seven, midway between acidic and alkaline. When you are about to throw up, your body produces more alkaline saliva, which tastes metallic, to neutralize the acidity of the vomit. If this metallic saliva happens on a consistent basis, you could be suffering from silent reflux, a condition in which stomach acid comes up into the back of the throat.

8. You see spots after a camera flashes.

The photoreceptors in the back of your eye convert light into electrical impulses that are sent to the brain to produce the images you see. “When a camera flash goes off, it’s so bright that it overstimulates the photoreceptors,” Elaine Icban, an assistant professor of clinical optometry at the New England College of Optometry, told statnews.com. While the photoreceptors are recovering, your brain “sees” nothing and fills in the blanks with spots.

9. You sneeze when you look up at the sun.

Photic sneeze reflex—sometimes called sun sneeze—is the name of this peculiar phenomenon. “The optic nerve, which senses a change in light, is very close to the trigeminal nerve, which controls a sneeze,” says Amy Rantala, MD, of the Mayo Clinic Health System in Eau Claire, Wisconsin. When you look up at the sun—or for that matter, when you step out of a dark room into bright light, whether it’s artificial or natural—your optic nerve constricts your pupils. Your trigeminal nerve may get the sensation that there is an irritation in the nose, triggering a sneeze.

10. Each cell in your body endures tens of thousands of DNA lesions every day.

Ultimately, this damage can alter a cell’s DNA and program it to destroy body tissue, resulting in the disease we know as cancer. Luckily, your body also contains the first line of defense: Enzymes are constantly checking DNA strands for signs of cancer and replacing damaged parts.

11. You get that stomach-in-yourthroat feeling on a roller coaster.

When a coaster comes over a crest and plummets, the seat belt may keep your rear in place, but some loosely connected internal organs—such as your stomach and intestines—get a little “air time.” Your nerves detect the movement, which registers as the feeling that your stomach has jumped all the way into your throat.

12. You get a charley horse.

“Charley horse” is a nice nickname for a nasty muscle cramp, commonly in your calf. One study found that the nerves inside the muscle can fire up to 150 electrical charges per second during a cramp, which is what forces the muscle to squeeze so tightly. The potential causes include dehydration, overexertion, and certain medications, such as diuretics.

13. You might smell like a rotten egg after eating meat.

Consuming too much meat (particularly red) plus

an inability to digest it well can lead to a sulfurous odor caused by the food’s sulfur-containing amino acids. One small study found that women rated men’s body odors as more attractive, more pleasant, and less intense after they had eaten no meat for two weeks compared with when they’d eaten red meat, according to the University of California, Berkeley.

14. You have an almost entirely new skeleton every ten years.

Old bone cells are constantly being replaced by new ones, a process called remodeling. This helps repair damage to the skeleton and prevents the accumulation of too much old bone, which can become brittle and break more easily.

15. You blink constantly.

The average person blinks 15 to 20 times every minute. Each time you blink, your eyelids spread a cocktail of oils and mucous secretions across the surface of your globes to keep them from drying out. Blinking also keeps eyes safe from potentially damaging stimuli, such as bright lights, and foreign bodies, such as dust.

16. You shiver when you’re cold.

“Your body is always trying to keep its temperature as close to 98.6 as possible,” says Dr. Rantala. “You shiver when you are cold in an effort to create heat” by contracting and expanding your muscles in quick bursts.