n air-filter with HEPA certification means it can be either Near HEPA or True HEPA. Near HEPA filters are usually those that can trap particles of 0.3 micron diameter with between 90% and 99.97% efficiency. However, a True HEPA must be at least 99.97% effective at removing all 0.3 micron particles from the air. Though most HEPA air-purifiers maintain industry standards, not all brands deliver the high standards of efficiency they claim. Some have been known to remove only 10% of allergens from the air. Some others are known to generate ozone while air-purifying. Therefore, you are advised to do some careful research before buying a HEPA air-purifier.
Some HEPA air purifiers are fitted with an additional UV light to kill airborne viruses and bacteria. This helps mitigate spreading of flu, TB (tuberculosis) and measles.
Some leading brands of HEPA air-purifiers are: Honeywell, Ionic Breeze, Hunter, IQAir, Austin Air, Friedrich, Oreck, Air-O-Swiss, Biozone, Calutech, Delonghi, Care, Allerair, Holmes, Blueair, Healthmate and Hamilton Beach. For controlling humidity (which also can cause allergic reactions), you can consider Danby Dehumidifier. If you wish to eliminate dust and improve indoor air quality, a high quality allergy relief vacuum cleaner from Miele or Dyson is a great investment.