My three-and-a-half-year-old son has been getting nosebleeds three or four times a week. Normally, these last only a few minutes and are easy to stop. However, today he had one that lasted 25 minutes and was very heavy. I have been told not to let him lie down when these nosebleeds occur. Is this good advice and, if so, why? How long should I wait to get him medical attention during these nosebleeds? His father says that they are caused by the weather changing from day to day and also when he does not take a nap. Could either one of these be true? His father does have very bad allergy/sinus problems. Could this be genetic?

J.M.

If he lies down during a nosebleed, the blood will run down the back of his throat. He may choke on this blood. Even if he doesn't choke on the blood, he will at least swallow it; swallowed blood will often cause nausea, vomiting and diarrhea. Finally, if the blood is running down the back of his throat and not out of his nose, how will you know when it has stopped? You may fail to gauge the seriousness of his nosebleed.

How long should you wait before seeking medical attention? You stated that "these last only a few minutes and are easy to stop." You must have some sense, by now, as to what a "typical" nosebleed is like for your son. If a nosebleed lasts much longer than this (e.g., his recent 25-minute gusher), you should take him to a doctor. You should, of course, take a few simple steps to encourage the nosebleed to stop spontaneously:

• First, have him gently blow his nose to clear out any blood clots.
  
• Next, spray an over-the-counter nasal decongestant into the bleeding nostril. (You should ask your son's pediatrician to recommend a spray that is safe for him to use in these circumstances.)
  
• Immediately after spraying his nose with decongestant, apply firm, direct pressure to his nose (a gentle but firm pinch using your thumb and index finger) for no less than five minutes.
  
• After five minutes, release pressure and watch carefully to see whether he is still bleeding. If he is, then spray his nose again, and again hold firm pressure for five minutes. If this fails to relieve his bleeding, you should take him to a doctor. Also, if he bleeds even when you are holding direct pressure (especially if you find that he is coughing and spluttering blood) you should take him at once to a doctor. If you cannot control his nosebleed with direct pressure, it is obviously a fairly serious nosebleed.
  

Incidentally, the persistence of this problem is worrisome. Even if his nosebleeds continue to be "quick ones," he should be taken to his pediatrician for an examination to find out what exactly is causing them.

The "weather change" theory refers to the observation that nosebleeds are more common during a prolonged hot or dry period. Think about chapped lips and imagine the same process happening in your nose. This is not a terribly accurate analogy, but it is true that we can minimize the risk of nosebleeds by taking steps to humidify or moisturize the nose.

Allergies also seem to provoke nosebleeds. There does, indeed, seem to be a hereditary component to the development of allergies. The allergies themselves are not inherited -- only the propensity for developing allergies.

I don't buy the "no nap" theory. Unless your son picks his nose more when he's tired and cranky, I have a hard time understanding why sleepiness would provoke a nosebleed.