‘Sick building syndrome’, a common issue for the occupants or users of school or office buildings, affects individuals in the form of repeated minor illnesses such as colds, flu and allergies. Whilst the causes of Sick Building Syndrome were unknown for a long period of time, it has now been shown to be a direct effect of poorly maintained ventilation systems. Ventilation systems left to harbour dirt and dust can become the home to potentially harmful particulates, meaning that when they are used, they have significant potential to spread dust and airborne microorganisms through a building. The Environmental Protection Agency has published studies showing that the air inside buildings can be as much as 70 times more polluted than the air outside where ventilation is not correctly maintained.