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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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.
Experts don't really know. One thing to consider: Laughing and crying are similar psychological reactions.