The constitution of yin deficiency is mostly caused by prolonged illness, sexual immorality, overeating warm and fragrant things, or emotional internal injuries, which leads to the loss of body fluid and the loss of the functions of nourishing viscera and skin of meridians, resulting in emaciation, haggard face, dry mouth and throat, sore throat, cold drinks, dry stool, short and red urine, even night sweats, or low fever in the afternoon and at night.