Common causes of
bloody noses can include a
sharp blow to the
nose, exposure to
high altitudes, and
cocaine abuse, though many people often experience them
regularly for no particular
reason.
Note: the first of the stories below is a bit unpleasant, and not for the squeamish. Consider yourself warned.
A friend of mine, Ben Emerson, experienced a number of bloody noses in Mexico City when our Spanish class took a trip there in 1998. The high altitude—some 2200 meters—caused this.
His first was in the hotel on our first night in Mexico. The blood flowed in prodigious quantities; Ben used kleenex to soak it up. He placed it in the toilet, which unfortunately clogged. The preëxisting urine mixed with the blood didn't make for a very pretty sight—nor, for that matter, for a pleasant odor. Having the best Spanish skills of the bunch in that room, I wrote a very apologetic note to the cleaning staff, and we left a very large tip for them.
A day or two later, we visited Teotihuacán. While climbing the Pyramid of the Sun, Ben's nose again began to bleed. But a man nearby came to his rescue, applying pressure to certain points on Ben's skull. The bleeding quickly subsided. It's a shame that this technique isn't well-known in the states, considering its (at least anecdotally reported) effectiveness.