What Causes Left Nose Bleeding? Some information you need to know about Unilateral Nose Bleeding Causes, What to do for Unilateral Nose Bleeding. What Causes Left Nose Bleeding? Unilateral Nose Bleeding Causes The most common nosebleeds are anterior nosebleeds. This group of nosebleeds usually originates from the blood vessels called the kiesselback plexus, where the…