What causes blood spot in phlegm?

Blood in phlegm: The most common origin of blood in phlegm is the nasal cavity including the sinuses.Dry, chaffed mucous membranes can bleed and this drips down the back of the throat and comes up with the phlegm.It can also come from bleeding gums or other sources in the mouth.Infrequently, it might arise from the stomach or lungs. If it persists, increases in frequency, duration or severity have it checked out.