Epistaxis, or nosebleed, can be caused by picking the nose, blowing the nose, high blood pressure, bleeding disorders, infections like the common cold, or head injuries. The first aid for a nosebleed involves having the person sit upright and pinch the nostrils while applying cold compresses to the nose and neck area to help constrict blood vessels and stop bleeding. Medical attention should be sought if bleeding does not stop or becomes heavy.