According to various studies, the indoor air is sometimes up to 5 times worse than the outside air from a pollution standpoint. Even if you have disposable filters you will see that those don’t really remove more than 10% of the pollutants, with the remaining 90% being there to roam free. Stuff like animal dander, mold spores, pollen and dust can accumulate and cause damage to your personal health. This type of materials will collect in the duct surfaces, air conditioner or any other similar place. Sure, the floor and furniture might be cleaned regularly but the other places might require professional equipment. If you don’t address them often then you will have to deal with plenty of health issues. Pollutants like these need to be removed fast and you can do that with the proper duct cleaning equipment. If you have a humidifier and air conditioner, then you have to address their air systems too as they can be filled with pollutants as well.