Heating and air conditioning ducts which are dark, damp and rich in "nutrients" provide an excellent breeding ground for mold, fungi and dust mites. These allergens can spread rapidly since the air ducts are used to heat and cool the house. Poor ventilation allowing fresh outside air indoors and dirty filters are also major contributors to unhealthy contaminates in the home. Mold and fungi can cause "discomfort", infections and commonly trigger allergic reactions.
While it is true that air duct cleaning alone does not cure health conditions like Asthma, allergies and other respiratory related conditions, vent cleaning does however, play an important role in prevention and treatment. By cleaning your HVAC system you will remove allergens like dust and mold from the duct work as well as residue from cigarette smoke.