Nosebleeds are very common. Most nosebleeds occur because of minor irritations or colds. The nose has an abundant supply of tiny blood vessels, which makes it easy for the nose to bleed. Air moving through the nose can dry and irritate the membranes lining the inside of the nose. The lining develops crusts that bleed when irritated by rubbing, picking, or blowing the nose.

The lining of the nose is more likley to become dry and irritated from low humidity and dry environment, allergic rhinitis, colds, or sinusitis. A deviated septum, foreign objects in the nose, or other nasal obstruction may cause also cause nosebleeds. A direct impact to the nose can also cause a nosebleed.

Most nosebleeds occur on the tip of the nasal septum, which contains many fragile, easily damaged blood vessels. More rarely, nosebleeds may occur higher on the septum or deeper in the nose. These higher or deeper nosebleeds may be harder to control.

Occasionally, nosebleeds may indicate other disorders such as bleeding disorders, hypertension, or arteriosclerosis. Hereditary hemorrhagic telangiectasia (also called HHT or Osler-Weber-Rendu syndrome, a disorder involving a vascular growth similar to a birthmark in the back of the nose) may be evidenced by nosebleeds.

Sometimes blood thinners such as Coumadin or aspirin may cause or worsen nosebleeds. Most nosebleeds begin on the septum -- the midline, vertical cartilage that separates the nasal chambers and is lined with fragile blood vessels. This form of nosebleed is not serious, and is usually easy to stop.

• Sudden trauma to the nose, very cold or very dry air, fragile blood vessels, nasal sprays, strenuous exercise, or picking the nose cause most nosebleeds.
• Recurrent nosebleeds may be a symptom of an underlying disorder such as high blood pressure, taking large doses of aspirin or blood-thinning medication, allergies, a bleeding disorder, or a tumor of the nose or sinuses.
• Most nosebleeds come from blood vessels in the front of the nose. Some are caused by bleeding from the back of the nose into the throat (posterior bleeding) -- these are more difficult to control and almost always require medical attention.