These Ultra filters from Filtrete capture 90% of large allergens like pet dander and mould spores from the air passing through the filter. They're even effective against microscopic allergens such as viruses, bacteria, smog, dust, and smoke. Each filter lasts up to 3 months. This model complies with the American Lung Association Health House Indoor Air Quality Guidelines. Furthermore, this product doesn't contain unnecessary antimicrobial chemicals and prevents the growth of mildew, fungi, bacteria, and mould when used as indicated.