The Odd Body Explained
Experts reveal the truth behind 13 of your body's lesser understood quirks.
Feb. 17, 2009— --
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.
For more health tips, check out the latest issue of Prevention, on shelves now!
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, PhD.
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.
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Experts don't really know. One thing to consider: Laughing and crying are similar psychological reactions.
"Both occur during states of high emotional arousal, involve lingering effects, and don't cleanly turn on and off," says Robert R. Provine, PhD, a psychologist at the University of Maryland, Baltimore County, and author of Laughter: A Scientific Investigation. We associate crying with sadness, but tearing up is an even more complex human response. Tears are triggered by a variety of emotions -- "by pain, sadness, and in some cases even extreme mirth. It's just the way we've evolved," says Lee Duffner, MD, a professor of ophthalmology at the University of Miami's Bascom Palmer Eye Institute.
As it turns out, that's good, because both laughter and crying can ease a stressful experience, probably by counteracting the effects of cortisol and adrenaline. So if you ever find yourself laughing until you cry, count yourself lucky.
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Body temperature is regulated in the brain by the hypothalamus, which signals the body to give off heat in warm conditions and trap heat (or shiver, generating heat in muscles) when it's cold.
Iron plays a role in this process, so people with anemia (commonly caused by iron deficiency) often feel chilly. Poor circulation -- due to high blood pressure or medications, among other culprits -- can leave the extremities deprived of heat. An underactive thyroid gland can also slow a person's metabolism to a point where the body generates insufficient warmth.
A recent study suggested there may even be a genetic predisposition to toward tolerance of cold. If you're the type who needs to wear sweaters and wool socks in the summer, eat iron-rich foods like lean red meats, beans, and dark green leafy vegetables, which can counter anemia. And avoid nicotine, which constricts blood vessels and leads to poor circulation.
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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, MD, 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.
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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.
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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, PhD, director of the Dows Institute for Dental Research.
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.
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