Causes of nosebleeds include trauma to the outside or inside of the nose and irritation from a cold, according to WebMD. Dry air and diseases such as acute sinusitis also cause nosebleeds. Other less likely causes include inability of the blood to clot, liver diseases and cancers in the nose.
Trauma to the outside of the nose may include a blow to the face, a fall or a car accident, explains Healthline. In these instances, nosebleeds may indicate a skull fracture, a broken nose or internal bleeding. Trauma inside the nose includes nose picking, which may damage the nasal membranes and cause nosebleeds.
Dry air causes the nasal membranes to dry out, which results in crusting inside the nose, Healthline advises. The crusting may become irritated and itchy, and if a person scratches his nose, it may bleed. Diseases and conditions that may cause nosebleeds include acute sinusitis, chronic sinusitis and a deviated septum, states Mayo Clinic.
Medications such as aspirin and blood thinners may lead to nosebleeds, Mayo Clinic explains. Antihistamines and decongestants may dry out the nasal membranes and cause nosebleeds. Allergies, cocaine use and chemical irritants such as ammonia may also cause the nose to bleed.
Less common causes of nosebleeds include leukemia, hereditary hemorrhagic telangiectasia, alcohol use and second trimester pregnancy, according to Mayo Clinic.