Humans naturally exhale hundreds of organic compounds that not only represent the physiological condition according to their presence and quantity but are also influenced by diet and potential disease metabolites. Within the entire world of living specimens, the recognition of odors is an essential pathway for transmitting information, which may range from the presence of potential predators to the transmission of information between individual organisms. Taking advantage of the specificity of information from the odors within exhaled breath (EB) dates back to the very beginning of medical practices. Later, during his pioneering analysis elucidating the composition of exhaled air, Pauling particularly emphasized the importance of recognizing selected biomarkers as indicators in clinical/medical diagnostics. Since then, a plethora of reports have aimed at correlating biomarkers present within the EB matrix to physiological conditions, diseases, and/or infections (Fig. 1). Despite the fact that the presence, origin, and physiological relevance of many components in breath are not yet fully understood, the composition of EB - and likewise, exhaled breath condensate (EBC) - reflects the biochemical processes and their "metabolic results" occurring within the body and may ideally be correlated to the physiological status, the progression of a disease, and the therapeutic progress/clinical treatment of patients. Given the noninvasiveness of the sampling procedure and the associated comfort for the patient, it is immediately evident that understanding the molecular profile of EB and its variations resulting from certain types of diseases provides a unique diagnostic window.
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