Leung HY, Leong PK, Chen J, Ko KM 
 Division of Life Science, Hong Kong University of Science and Technology, Clear water bay, Hong Kong SAR.
Research on allergy has recently uncovered an apparent co-occurrence of allergies in skin and the lungs, a phenomenon that has been coined "atopic march". A positive correlation has been found between gut microbiota at birth and the development of asthma and skin eczema later in life. Chinese medicine has long described a functional relationship between the large intestine and the lungs, and between the lungs and skin. In this short article, we examined the evidence in support of these inter-organ physiological/pathological relationships. In addition to the clinical observation of the relationship between the composition of gut microbiota at birth and the development of asthma later in childhood, gut microorganisms have also been shown to exert a protective effect on bacteria-induced pneumonia in experimental animals. Genetic predisposition was also found to play an important role in the co-existence of certain diseases of lung and skin. Despite the fact that the mechanism(s) underlying the connection of immune systems between two organs (such as the large intestine and the lungs) is still not clearly understood, it is the first time to correlate the relationship among gut, lung and skin based on recent clinical studies in relation to the Zang-Fu Theory in Chinese medicine. Future investigation of the gut-lung and lung-skin axes in terms of physiological/pathological relationships may help to provide a greater understanding of the pathogenesis of allergies, possibly establishing relevance to the Zang-Fu Theory in Chinese medicine.