HOW COME? Why we get nosebleeds

Why do we sometimes get nosebleeds? asks reader Nicki Baran.Nosebleeds can be embarrassing (the marching-band nosebleed), irritating (the white-shirt nosebleed) and even scary (the middle-of-the-night nosebleed). But thankfully, most nosebleeds are more annoying than serious.

What's leaking in a nosebleed is one or more tiny blood vessels, the capillaries, lying just under the surface. As we breathe in air, it passes over these vessels, and is warmed and humidified. But because the capillaries are so tiny and so unprotected, they're very easy to break. Blood suddenly trickling from your nose usually means that an injured vessel has sprung a small leak.

Most of the time, the leaky capillary is part of a network of blood vessels on the septum, the hard wall of cartilage dividing the nose in two. And more than 90 percent of the time, the blood is coming from a capillary in the front (or "anterior") of the nose.

Nosebleeds happen most in kids aged 2 to 10, but they also occur in adults, especially those over 50. That annoying trickle of blood emerging from a nostril is most likely to happen in winter, when room air is warm and dry. But in summer, air-conditioning can create an extra-dry room, too. When air is very dry, the nose becomes parched, like your throat in the desert. As the lining dries out, it shrinks from plump to thin -- leaving blood vessels extra-vulnerable.

Besides dry air, the laundry list of nosebleed triggers includes a bump to the nose or face; an allergy or cold with lots of sneezing, coughing and nose-blowing; antihistamine nasal sprays; and anti-clotting drugs like aspirin. But one of the main culprits -- in fact, it's probably number one on the list -- is nose-picking.

While most bleeding comes from the front, some nosebleeds start in the back ("posterior") of the nose, and can indicate a more serious cause. If you get hit in the nose by, say, a soccer ball, your nose may bleed from both the front and the back, with blood trickling down your throat. Any kind of serious injury to the head or face should send you to the nearest emergency room. In fact, any nosebleed that just won't stop requires a doctor's attention.

Once an ordinary nosebleed starts, blood vessels usually form clots and close off, and the bleeding ends on its own. If a nosebleed doesn't stop quickly, you can help by keeping your head upright, leaning forward a bit, and gently pinching your nostrils shut for up to 10 minutes. Then treat your nose like a fragile flower for 24 hours -- no scratching, picking, or blowing -- so that vessels can heal.