Understanding the viscera-related theory that the lung and large intestine are exterior-interiorly related.

Pairing of the viscera and bowels is an important theory, which provides guidance to traditional Chinese medicine (TCM) clinical practice. Investigating this theory has been the focus of research on the basic theory of TCM. Recently, researchers have performed many studies on the theory that the lung and large intestine are exterior-interiorly related, which is a different point of view to that of previous literature, recent clinical studies and experimental studies, and these recent studies have enforced the theoretical connotation of the statement. However, there are problems in some of these studies including recent clinical studies and experimental studies. In the current article, literature on the viscera-related theory of the lung and large intestine are exterior-interiorly related is reviewed from physiological, pathological, and clinical views, and some opinions on the current research status are discussed.