Breath testing is used to diagnose a range of conditions from lactose and fructose intolerance to overgrowth of bacteria in the bowel. It is useful in people with symptoms attributed to food intolerance or IBS. It works by detecting hydrogen on the breath which is broken down by bacteria in the gut. In people who do not metabolise lactose and other test sugars, bacteria in the colon break it down to hydrogen which is detected by the analyser. To detect bacterial overgrowth in the gut a sugar absorbed by no one is used called lactulose. Bacterial overgrowth which can be treated with courses of non-absorbed antibiotics, is associated with symptoms of bloating, cramping and diarrhoea.