The human body is exposed to a multitude of microbes and infectious organisms throughout life. Many of these organisms colonise the
skin, gastrointestinal tract (GIT) and airway. We now recognise that this colonisation includes the lower airway, previously thought to be
sterile. These colonising organisms play an important role in disease prevention, including an array of chronic inflammatory conditions that
are unrelated to infectious diseases. However, new evidence of immune dysregulation suggests that early colonisation, especially of the GIT
and airway, by pathogenic micro-organisms, has deleterious effects that may contribute to the potential to induce chronic inflammation in
young children, which may only express itself in adult life.