When an adult has a nosebleed for no apparent reason, it could be related to medications, health conditions, or simply dry air. intranasal tumors. Any of these conditions can cause the surface blood vessels in the nose to bleed. Sudden and inexplicable nosebleeds may seem scary, but typically they're not. To put you at ease in case you have one, we've put together a . The lining of your nose contains many tiny blood vessels that lie close to the surface and are easily damaged. The two most common causes of nosebleeds are: Dry air — when your nasal membranes dry out, they're more susceptible to bleeding and infections. Pinch your nose. Use your thumb and index finger to pinch both nostrils shut, even if only one side is bleeding. Breathe through your mouth. Continue to pinch for 10 to 15 minutes by the clock. This maneuver puts pressure on the bleeding point on the nasal septum and often stops the flow of blood. If the bleeding is coming from higher up, the.