Wind, heat and toxin are the main causes of epidemic parotitis. In winter and spring, wind, heat and toxin enter the human body through the mouth and nose. They attack Shaoyang meridians along their courses. In this case, meridians will get stagnated, causing the obstruction in qi and blood circulation. As a result, the pathogenic factors stagnate in the parotidean regions below ears. Therefore, disseminated swelling, distension and pain occur subauricularly in the parotidean regions, developing into epidemic parotitis. Deficiency of healthy qi is the endogenous cause of the occurrence and development of the disease. The delicacy of the infantile lung and the weak external defence make infants extremely susceptible to the attack by exogenous pathogenic factors.

When pathogenic factors block Shaoyang meridians, healthy qi and pathogenic factors will struggle with each other. In this case, deficient healthy qi fails to keep pathogenic factor in the outside. Consequently, pathogenic factors will get accumulated retroauricularly, developing into parotidean swelling and distension. Besides, Shaoyang meridians and Jueyin meridians are exteriorly-interiorly related. Thus when pathogenic factors sink in Jueyin meridians, swelling and pain of testis or pain of lower abdomen will occur. Finally, excessive pathogenic factors will stir up the liver wind and block the mind, giving rise to unconsciousness and clonic convulsion.