A poorly maintained air-conditioning system can occasionally promote the growth and spread of microorganisms, such as Legionella pneumophila, the infectious agent responsible for Legionnaires' disease, or thermophilic actinomycetes,[10] but as long as the air conditioner is kept clean these health hazards can be avoided. Conversely, air conditioning, including filtration, humidification, cooling, disinfection, etc., can be used to provide a clean, safe, hypoallergenic atmosphere in hospital operating rooms and other environments where an appropriate atmosphere is critical to patient safety and well-being. Air conditioning can have a positive effect on sufferers of allergies and asthma.
In serious heat waves, air conditioning can save the lives of the elderly. Some local authorities even set up public cooling centers for the benefit of those without air conditioning at home.
Poorly operating air conditioning systems can generate sound levels that contribute to hearing loss, if exposures are endured over a long term[citation needed]. These levels are similar to the exposure of living near a busy highway or airport for a considerable length of time.[citation needed] Properly functioning air conditioners are much quieter.
In many people, the air flow (draught) caused by an otherwise clean air conditioning system of a car may cause acute sinusitis.
Source: http://en.wikipedia.org/wiki/Air_conditioning#History
