Yin and Yang are the two platforms for identifying disease categories. Under normal conditions, the body maintains a relative balance between Yin and Yang. Yin deficiency is called Yin deficiency, and Yin deficiency is associated with heat. Generally speaking, Yin deficiency and internal heat are mostly seen as generalized signs of deficiency heat. In the case of Yin deficiency, the clinical symptoms of Yin deficiency and internal heat are mostly concentrated in one part of the body, such as dry mouth, dry lips, hot flashes, toothache, epistaxis, sore throat, red cheek, dry stool, short red urine, etc. The patient’s tongue is red with little or no moss. Lung yin deficiency is usually caused by weakness due to prolonged illness, or evil heat that lingers in the lungs for a long time and damages lung yin. Or due to excessive sweating that injures lung yin and fails to moisten the lung. If Yin deficiency cannot control Yang, then Yin deficiency and fire can be seen. The symptoms are dry cough without sputum, or sputum with little stickiness, coughing with blood and dry throat, or hoarseness, afternoon hot flashes, night sweats, emaciation, redness of the cheekbones, and thin pulse. Liver Yin deficiency, because it cannot nourish the head and eyes, causes dizziness and tinnitus, and dryness of the eyes; Yin deficiency produces internal heat, so hot flashes and night sweats, and dryness of the throat. A red tongue with little fluid and a thin pulse is a sign of Yin deficiency. Yin deficiency and fire are mostly manifested as a chronic process. The more Yin is deficient, the more fire is likely to flourish, and the more fire flourishes, the more Yin is injured, forming a vicious circle, and the condition becomes increasingly aggravated.