Occasionally, our breath reveals more about us than we'd perhaps like – that we indulged in a late-night kebab, for example, or our penchant for garlic-laden French cooking.
But even the sweetest of breath contains a lot more than just carbon dioxide and water. An immensely complex array of chemicals – including nitrous oxide, ammonia and a vast number of volatile organic compounds (VOCs) – is excreted from the body via our breath. Those chemicals are generated within the body by our normal metabolic processes, and when those go wrong, as they do when we are ill, our breath profile – or "breathprint" – changes.
Jim Reynolds of Loughborough University analyses and interprets breath VOC profiles. The idea is that breath profiling will one day allow non-invasive diagnosis for a wide range of illnesses. "We're looking for the chemical signatures of diseases such as lung cancer, chronic obstructive pulmonary disease and childhood asthma," says Reynolds.
His team uses a technique called gas chromatography, which takes complex mixtures of chemicals and separates them by their different boiling points. These are then fed into a mass spectrometer or ion mobility spectrometer, which show the structure of each separated chemical. In this way, the breathprint can be visualised and studied.
With these techniques, scientists are, in a way, trying to replicate the ability of dogs to discern unique human odours. A dog's nose can distinguish breath samples from cancer patients from carefully matched control samples, as reported this week by Japanese researchers: a labrador retriever correctly identified 33 of 36 people with bowel cancer after sniffing their breath.
But, brilliant as the idea of Dr Dog may be, how far are we from using breath profiling in the GP's surgery? Cristina Guallar-Hoyas, a research student at Loughborough specialising in breath profiling, points out that for some diseases, diagnosis is not as simple as monitoring a single compound – it is often a more subtle change in the overall breath profile that is significant. And her colleague Matthew Turner adds that, although we can identify many of the compounds in our breath, we don't always know – yet – which of our bodily organs has produced those compounds, and hence where any illness may be lurking.
