Thanks for the question Gloria!
If you suffer from allergies or asthma, you should take a look at your HVAC system. Most people don't realize that indoor air pollution levels are actually greater than those outdoors. Without proper maintenance, dust mites, pet dander, pollen, and mold will collect in your air filter and duct work.
The first line of defense against these tiny particles are your air filters. They should be replaced every month or so, but even more during allergy season. There are different types of air filters to chose from. High-efficiency and HEPA filters remove the most particles, but have been found to put more stress on your HVAC system. Medium-efficiency filters are reasonably effective at removing small to large particle and can do the job for most people.
Particles that do happen to get past your filter will collect inside your unit and duct work. When combined with moisture, it makes the perfect breeding ground for mold and bacteria. UV lights can be installed in your HVAC system to combat many types of fungi, bacteria, germs, viruses and pathogens. While is hasn't been proven that clean ducts benefit your health, it only makes sense.
In the end, the best defense against allergies and asthma is proper installation and regular maintenance of your HVAC system. Not only will you have better air quality, but it will also save you money in the long run.