They are able to expel exterior pathogens(Evil Qi) such as Wind, Cold, Dampness, Summer Heat. The Chinese wearing it for prevention of seasonal flu, common cold and child indigestion and so on. The aromatic odor emitted by the herbs can stimulate human nasal mucosa to increase the secretion of antibody- immunoglobulin A(IgA) on the nasal mucosa which can kill virus and thus reducing the chance of catching a cold or a flu.