What causes goose bumps? and other trivia

1. What causes goose bumps?
Goose bumps (scientific name: piloerection) pop up when you're cold or
afraid. A tiny muscle at the base of each body hair contracts;
together, they appear as naked bumps on the flesh. They made sense
eons ago, when humans still had a natural "fur coat." Back then,
fluffing your ruff would warm the body by trapping an insulating layer
of air between the hairs. And standing your hair on end was
intimidating to predators or enemies (picture a cat facing off with a
dog). Evolution has since stripped humans of their pelts. Now goose
bumps are, of course, no medical issue. If you're uncomfortable
showing off your vestigial physiognomy, dress warmly, place yourself
in calm environments, and avoid horror flicks.
2. Why does chopping onions make you tear up?
When you cut into an onion, you rupture its cells, releasing enzymes
that produce a gas called propanethial sulfoxide. Once that gas
reaches your eyes, it reacts with tears to produce a mild sulfuric
acid. And that hurts. The brain then signals the eyes' tear glands to
produce more liquid to flush the stuff out. The more you chop, the
more irritating gas you produce and the more tears you shed. "The
onion's chemical reaction is a defense mechanism that evolved to repel
pests," explains University of Wisconsin-Madison horticultural
professor Irwin Goldman, Ph.D. Keep the stinging and crying to a
minimum by chilling an onion in the freezer before cutting it; cold
temperatures slow release of the enzymes. The highest concentration of
enzymes is at the bottom of the onion, so cut it last to postpone the
weeping (and the irritation) for as long as possible.
3. Why do your joints crack?
The most common type of joint in the human body is the diarthrodial
joint—knuckles and shoulders are examples—in which two bones come
together in a capsule. Inside that joint capsule is a lubricant called
synovial fluid, which contains dissolved gases. When you stretch the
joint, you're actually compressing it and the fluid within, forcing
those nitrogen-rich gases to escape the synovial solution. The release
of "air" within the joint capsule is what you hear as a "pop." Once
the gas is released, the joint is a bit more flexible (enabling you to
go a little further in a yoga pose, for example). But you've probably
noticed that you can't immediately crack the same joint again. That's
because the gases released in a pop must first reabsorb into the
fluid, a process that takes 15 to 30 minutes. If you habitually crack
your knuckles to relieve tension, try concentrating on your breath for
30 seconds instead. Knuckle cracking doesn't lead to arthritis, but it
can lead to decreased grip strength.
5. What makes your eyelid twitch?
This annoyingly common condition is known as eyelid myokymia. Not a
lot is known about eye twitches, which are more likely to occur in the
lower eyelid than in the upper, though they're probably caused by the
misfiring of a nerve. But experts know that fatigue, stress, and
caffeine all increase the likelihood of the pesky twitching. So do
eyestrain, poor nutrition, excessive alcohol intake, and allergies.
Fortunately, eye twitching is almost always benign and usually goes
away by itself. To put an end to a bout of the eye flutters, cut down
on coffee and alcohol and give your eyes—and your whole body—a good
night's rest.
7. Is it true that your ears grow throughout life?
Yes, the outer ears do. Starting at birth, the ears are,
proportionally, the body's largest feature, with a Spock-like
prominence. They grow rapidly until about age 10, then slow to the
languid pace of about 0.22 millimeter per year, according to a study
by Britain's Royal College of General Practitioners. Other studies
show that the earlobe itself also lengthens throughout life (men have
longer lobes than women). However, the size of the ear canal, which is
formed by bone and cartilage, does not increase into old age.
8. Is it true that all babies are born without a single freckle?
Babies, of course, can be born with birthmarks and "beauty marks," but
it's true that upon entering the world they have no freckles, which
the skin produces (using excess pigment) in response to sun exposure.
As babies get out in the sun, those with fair complexions and light
eyes will be especially prone to developing freckles (and will have a
higher likelihood of skin cancer and melanoma later in life). "Those
freckles on the redheaded kid's cheeks aren't cute—they're sun
damage," says Robin Ashinoff, M.D., director of dermatologic surgery
at Hackensack University Medical Center. "And freckles probably also
indicate damage to the DNA in your skin cells." Children and adults
alike should have their freckles monitored regularly by a
dermatologist and vigilantly use sunscreen of SPF 30 or higher.
9. What causes the feeling of "pins and needles"?
Called paresthesia, pins and needles are caused by blocked blood flow
to a pressed nerve. If you sit too long in an awkward position—or even
just with your legs crossed—you may press hard enough on a nerve to
interrupt its signaling to the brain, causing your feet, for example,
to "fall asleep," or go numb. This is not the same as a pinched nerve,
a longer-lasting condition that occurs when a part of the body,
swollen because of injury or misalignment, applies steady pressure on
a nerve. Paresthesia is usually felt in the extremities—hands, feet,
and ankles. That crazy-making prickly sensation is the resumption of
pain messages to the brain. Simply changing your position is almost
always enough to allow the nerve to resume communication. But prickly
feelings more rarely can be symptoms of diseases as diverse and
serious as diabetes, lupus, and MS. If your pins and needles don't
resolve quickly with a change of body position, see a doctor.
10. Why are there rings or halos around lights when you drive at night?
This phenomenon falls under the category of "spherical
aberration"—just one of several examples of how the human eye is
optically imperfect. In daylight, the pupil narrows to a very small
opening, allowing light to hit the very center of the lens. At night,
when the pupil dilates dramatically to allow maximum light to enter,
your eye is using a much larger swath of its lens to see. "The farther
out on the lens you go, the less perfect the optics are," says
Duffner. "And as you get off center, those light rays won't be focused
to the center of the eye." You see circles, well, because your lens is
round. Almost everyone sees these rings, and if you've always seen
them, you're probably just fine, he says. But halos can also be caused
by opacities in the lens—a sign of cataracts. So if seeing halos is
new to you, see a doctor for a cataract exam.
11. Can "cankles" actually be good for you?
Maybe. Scientists haven't studied the significance of ankle shape, but
other research on fat distribution may point to an answer. Ankles that
have lost a bit of definition over the years and appear to merge with
the calf (hence the hybrid word) might actually improve your health
profile, as long as you're not seriously overweight. Fat stored in the
intra-abdominal region—in and around the organs—correlates highly with
metabolic disorders, such as type 2 diabetes; fat in the legs is least
linked with these maladies. Wendy Kohrt, Ph.D., professor of medicine
at the University of Colorado Denver, found that postmenopausal women
who had a relatively high level of leg fat (as opposed to abdominal
fat) had lower risks of heart disease, hypertension, and type 2
diabetes. Leg fat, she explains, may protect postmenopausal women by
drawing triglycerides out of the bloodstream, where they constitute a
risk factor, and into fat deposits in the legs and, possibly, cankles.
Her findings suggest that removing lower-body fat cells—by
liposuction, say—may not be a good idea: Women who do may begin to add
weight to fat cells in the more dangerous midriff zone, she suspects.
12. How could chewing sugarless gum and eating cheese prevent cavities?
Every time you eat, bacteria in your mouth react chemically with the
food and introduce an organic acid that can cause tooth decay. By
dislodging food, rinsing teeth, and diluting acid, saliva counters
this process. The key is to keep it flowing, which is where chewing
gum—or at least chewing—comes in. "We showed that the simple
mechanical act of chewing stimulates salivary flow," says James Wefel,
Ph.D., director of the Dows Institute for Dental Research in Iowa
City. As for cheese, its fats may act as a protective barrier for the
teeth; it also contains calcium and phosphate, which may discourage
decay and strengthen teeth. What this all means to you: Limit
between-meal nibbles, thereby reducing the number of acid exposures.
Chew sugarless gum after meals. Or do like the French and finish your
meal with a few pieces of cheese.
13. Why does your side hurt sometimes when you laugh really hard?
Two classic causes of a "side stitch" are running and prolonged
laughter. Those activities have at least one thing in common: exertion
of the diaphragm. "When you laugh really hard, you're sucking in a lot
of air, which fills the lungs and pushes down on the diaphragm while
the abdominal muscles are also contracting and pushing up on the
diaphragm," explains Robert Gotlin, D.O., a sports physician at Beth
Israel Medical Center and former director of orthopedic rehab with the
New York Knicks. All of which, of course, happens scores of times each
minute when you're howling. The repeated compression can produce a
muscle spasm that we all know as a stitch. "Sometimes when you laugh a
lot, you get a pain in your right arm as well as the side stitch.
That's because the nerve that supplies the diaphragm also goes to the
right shoulder," he says. So, in addition to busting your gut, a
hearty laugh can mistakenly make you think you're having a heart
attack. Try breaking the rapid cycle of diaphragm punishment that we
call laughter by slow, deep breathing between fits of hysteria. And
avoid eating big meals, which draw blood to the stomach, before
settling in for an evening of "30 Rock" reruns.