Most internal diseases in TCM are caused by endogenous pathogenic factors. Emotional damages may cause depressive syndrome, mania-depressive syndrome, wind stroke, vertigo and goiter. Overstrain may cause edema, diabetes, impotence and spermorrhea. Improper diet may cause stomachache, vomiting, belching and hiccup.

Among the causes of internal diseases, there are some endogenous pathogenic factors secondary to the dysfunction of internal organs. These endogenous pathogenic factors may cause disorders with the manifestations similar to those caused by six exogenous pathogenic factors and they are traditionally called five endogenous pathogenic factors, i.e., endogenous wind, endogenous cold, endogenous dampness, endogenous dryness and endogenous fire. For example, endogenous wind may cause syndromes such as vertigo and apoplexy with the manifestations of dizziness, numbness and convulsion of limbs.

Endogenous cold may cause syndromes such as stomachache and abdominal pain with manifestations of cold limbs, pale complexion, vomiting of clear fluid, and abdominal cold pain. Endogenous dryness may bring about the syndromes such as cough and constipation with the manifestations of dry mouth and throat, cough without sputum, dry skin and constipation with dry stools. Endogenous fire may lead to hemorrhagic syndrome, depressive syndrome and wind stroke with manifestations of headache, red eyes, restlessness, irritability, dry and bitter mouth, etc. Endogenous dampness may cause such disorders as diarrhea and epigastric flatulence with manifestations of nausea, vomiting, poor appetite, fullness of abdomen, loose stools, etc.