Nosebleeds are at best annoying, and at worst, life-threatening. Usually the site of bleeding is the front part of the septum separating the nostrils. The most common causes of bleeding in this area are minor trauma and dryness of the tissue. Bleeding further back in the nasal cavity is less common and may have a more serious cause.
Common Causes
One of the most common causes of bloody noses is local trauma to the area from blowing or picking the nose. This mechanism injures the superficial blood vessels of the nasal septum, causing them to bleed. More severe trauma, as in a nasal fracture, may also lead to blood loss. Dryness of the tissue overlying these vessels also makes them more prone to bleeding. Low humidity, cold air or heated air from a furnace may lead to drying, which causes thinning of the mucosa of the nose. This scenario makes nosebleeds more common in the winter, according to MedlinePlus.
Less Common Causes
Bloody noses may be caused by localized infections such as the common cold or sinusitis. Allergies may also disrupt the nasal mucosa. If the septum is deviated or perforated, the individual is more prone to nosebleeds. Foreign material in the nose is usually a problem associated with childhood, and may lead to bleeding. Polyps, or small, benign growths in the nasal cavity, increase the risk of bleeding. Exposure to ammonia, cigarette smoke, environmental irritants or nasal spray medication may cause a bloody nose. Oral medications that affect the blood clotting mechanism increase the chances of experiencing a nosebleed. Medicines such as aspirin, ibuprofen or warfarin may be implicated, according to "American Family Physician."
Rare Causes
Liver disease---cirrhosis, for example---may predispose one to nosebleeds due to impaired blood clotting. Alcohol use may cause bloody noses either through liver damage or direct toxic effects on the cells responsible for blood clotting. Diseases that may have the same effect include hemophilia; idiopathic thrombocytopenic purpura, which is a platelet disorder; and leukemia. Lupus, AIDS and sarcoidosis are systemic illnesses that can be causes of nosebleeds, notes MayoClinic.com. Cardiovascular diseases like hypertension and arteriosclerosis are sometimes responsible for nosebleeds, usually in the elderly. According to The Merck Manual for Healthcare Professionals, a rare disorder called Rendu-Osler-Weber syndrome is characterized by abnormal blood vessels of the face, lips, fingers, toes, and oral and nasal mucosa. Similarly, local malformations of the blood vessels of the nasal septum may result in a nosebleed.
