Old phlegm in the throat can be related to lung diseases, and may also be related to other respiratory diseases, cardiovascular diseases and so on. 1. Lung diseases: such as tuberculosis, pneumonia, lung abscess, etc., can trigger the symptoms of phlegm. 2. Other respiratory diseases: acute and chronic pharyngitis, tonsillitis and sinusitis, rhinitis, etc., can also trigger symptoms of phlegm. 3. Cardiovascular diseases, such as acute pulmonary edema, pulmonary hemorrhage and pulmonary embolism, are also common causes of phlegm. 4. Other factors: such as long-term in the dust environment, can stimulate the mucous membrane in the throat area, resulting in increased secretion of the glands, and then phlegm performance. The phenomenon of frequent phlegm has many causes. Be sure to consult a doctor to confirm the cause of the disease, and combined with the cause of the disease, follow the doctor’s arrangements for treatment.