Internal heat and external cold after a cold is often referred to as “cold fire”, which is caused by the external wind and cold evil, the body’s righteousness is insufficient to resist the evil, and the exterior of the body is not solid and a series of wind and cold symptoms appear, such as light fever, heavy cold, fear of wind, nasal congestion and runny nose. If the symptoms are mismanaged, the superficial evil is not relieved, heat is turned into heat in the lung, the lung meridian is depressed with heat, the elevation of qi is out of order, and the lung qi is rebellious, then coughing, coughing yellow sputum, and wheezing cannot lie down. The lung and the large intestine are in close proximity to each other. If the lung heat is not purged, the intestines will become dry and the fluids will be dried up, resulting in bad breath, constipation and other symptoms of internal heat.