Epistaxis (ep-ih-STAK-sis), or nosebleed, occurs when small blood vessels (known as capillaries) break within the tissue lining of the nose.
The more common "anterior" nosebleed starts from the front of the nose and is caused by irritation and lack of moisture in the nasal membranes. Dry air or heated indoor air irritates and dries out nasal membranes, causing crusts that may itch and then bleed when scratched or picked.
Colds and allergies also can cause nosebleeds by aggravating the lining, and repeated nose blowing and medications like antihistamines and decongestants can dry out and irritate the nasal passages.
"Posterior" nosebleeds occur less frequently, but can be more serious since they are mostly associated with nose or face injuries. Bleeding starts in the deepest part of the nose and flows down the back of the throat.
Nosebleeds can seem frightening, but are rarely cause for alarm. Most can be easily treated at home. Frequent nosebleeds might indicate a more serious problem, however. If nosebleeds happen often or bleed for a long time, contact your doctor. If a nosebleed is the result of a head injury, is accompanied by dizziness or weakness, or doesn't stop after two attempts of applying pressure for 10-15 minutes each, go to the emergency room immediately.
All A to Z dictionary entries are regularly reviewed by KidsHealth medical experts.
