The nose is a part of the body rich in blood vessels (vascular) and is situated in a vulnerable position as it protrudes on the face. As a result, trauma to the face can cause nasal injury and bleeding. The bleeding may be profuse, or simply a minor complication. Nosebleeds can occur spontaneously when the nasal membranes dry out and crack. This is common in dry climates, or during the winter months when the air is dry and warm from household heaters. People are more susceptible to bleeding if they are taking medications which prevent normal blood clotting (warfarin, aspirin, or any anti–inflammatory medication). In this situation, even a minor trauma could result in significant bleeding.

The incidence of nosebleeds is higher during the colder winter months when upper respiratory infections are more frequent, and the temperature and humidity fluctuate more dramatically. In addition, changes from a bitter cold outside environment to a warm, dry, heated home results in drying and changes in the nose which will make it more susceptible to bleeding. Nosebleeds also occur in hot dry climates with low humidity, or when there is a change in the seasons.

The following factors predispose people to nosebleeds

• Infection.
• Trauma, including self–induced by nose picking.
• Allergic and non–allergic rhinitis.
• Hypertension (high blood pressure).
• Use of blood thinning medications.
• Alcohol abuse.
• Less common causes include tumors and inherited bleeding problems.

Source: www.medicinenet.com