Blood in the oral cavity can come from an accidental cut or infection inside the mouth or on the gums. Blood may also be traveling to the mouth from another location, like the sinus cavity or the stomach. Less common causes for blood in the mouth include cancer and head trauma.
The presence of blood in the mouth can indicate several conditions, not all of which are inherently dangerous. Post-operative bleeding from the nose or the throat, severe tonsillitis, dental work, oral surgery and accidental wounds are among the most common causes of blood in the mouth. Less frequently, oral cancer, head trauma and malignancies in the nasal cavity, larynx or esophagus cause blood to collect in the mouth. If in doubt as to the cause of the bleeding, it may be prudent to contact a doctor.