Having a central air conditioning and heating system means that there is a system of ducts inside of the walls of your home. Even though the system is sealed as well as possible, there can still develop a buildup of dust and debris inside the ducts over time. This can lead to poor air quality, and possibly even cause health problems such as asthma or worsened allergies. The problem is that there is no easy way for a homeowner to access these ducts.
There are however many professional duct cleaning companies that can take care of the problem for you. They have tools that will first dislodge the dirt and debris, and then they use high powered vacuums to clean it up. If necessary, they also use chemicals to kill microbes in your system to lessen the chance of anything harmful growing inside the ducts.
Do your research, find a company that gets good ratings and reviews, and soon you will be breathing fresher air.