I have a nose bleed, what could be wrong?

Some thoughts...: Nosebleeds can be due to many things that cause one of the little veins on the inside of a nose (usually the middle septum) to crack and leak temporarily. Heavy breathing in sports, hot or cold air, allergies, nose-picking, colds, constipation straining, etc..., are some causes of nosebleeds. She who bleeds "too often" or "too long" can have her blood checked to see if her blood clots too slowly.