Body Facts

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).

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.

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.

You have 2 million tiny hairs in your inner ear.

Unlike hair growing on the surface of your ears, the presence of hairs, or "stereocilia," deep inside your head aren't considered a hygiene lapse. Instead, they're a vitally important part of your ability to hear, responsible for changing physical sound waves into electrical signals that can be understood by your brain, according to the British Hearing Research Trust.