The completely sealed system in the Miele S140 to S168 Little Giant, Universal Uprights and S194 & H1 Quickstep or Tactical, when equipped with a Certified HEPA Filter, will retain 99.97% of pollens, household dust, dust mite droppings and other allergens as small as 0.3 ?m in size. This filter is highly recommended for those who have dust related allergies or asthma.