External Wind is one of the six adverse influences (Wind, Heat, Dryness, Cold, Dampness, Summer Heat), and was considered by ancient physicians as the preeminent pathogenic force in the development of illness - the provocation of a hundred diseases. External Wind is insidious: like a cold draft enters a house through small cracks in the walls, Wind can invade the body when it is weak or undefended. The concept of External Wind not only includes the movement of air, but any sudden changes in the external environment that disrupt the organism's ability to adapt. The first line of defense is the body's external envelope, the skin and subcutaneous nerves, vessels and muscles. Poor circulation of Blood, Qi, and Wei throughout the surface layer makes the individual vulnerable to attack by External Wind that penetrates through the pores and channels, especially in the regions of the head, neck, upper back, and chest. Attack by External Wind also prepares the way for invasion by other pathogenic entities such as Heat or Dampness as if these other adverse influences ride "piggy-back" on the Wind. Once it penetrates the external regions, External Wind (particularly if it is joined with Heat, Cold, or Dampness) can lodge within the channels (Jing-luo), resulting in the obstruction of Qi, Blood, and Moisture circulation. This obstruction of surface circulation often underlies arthritic and rheumatic complaints as well as recurrent headaches and respiratory allergies. Purge External Wind enables the organism to mobilize its defensive resources at the surface by activating Qi, Blood, and Wei in the channels and blood vessels of the skin and muscles.*