Filtering the air with a HEPA filter attached to your ductwork is the best way to help someone with sensitivity to dust and allergens. Most HEPA filters have three layers of filtration. The pre-filter catches larger particles such as hair. The carbon filter is an important part of this process because it acts like a sponge and has lots of holes and burrows for chemicals to sit. The third filter is a certified HEPA filter, which collects 99.97% of particles down to 0.3 microns.