Yin Qiao is a well known formula for treating the early stage of febrile diseases. In our culture, modern pharmaceuticals, especially antibiotics, often fail to deal completely with the various infections transmitted by airborne pathogens or intimate contact between people. Antibiotics can, with repeated use, actually weaken the body\'s defenses against illness, especially for viral syndromes for which they are ineffective. In Chinese medicine, Defensive (wei) qi is responsible for protecting the body from invasion by pathogenic factors such as Wind, Heat, and Cold. Wei qi circulates in the outer layers of the body, between the skin and muscles; its function is to prevent external pathogens from penetrating to deeper levels of the body where they might affect the functioning of the organs. A vacuity of wei qi makes a person prone to catching colds and flus more frequently. The failure of many people to take the "common cold" seriously often results in further weakened immunity and feelings of chronic ill health. When an exterior Wind Heat condition is not treated properly, the pathogen can penetrate to the shao yang level, midway between the interior and exterior, where it might remain entrenched. This usually manifests asa an internal Heat or Damp Heat condition. The leftover Heat or Damp Heat can further damage the Qi and Yin of the body, resulting in vacuity states which leave one open to further invasion by "external evils."