Pathologic extra-oral halitosis can be subdivided into non-blood-borne halitosis, such as halitosis from respiratory tract or upper alimentary tract, and blood-borne halitosis, including hepatic disease, cystinosis, trimethylaminuria and so on. There are volatile organic compounds in our breath that cause halitosis, and in some circumstances reflects certain diseases. This review mainly focused on different mechanisms of various extra-oral diseases and their relationship with extra-oral halitosis.
