There are two different types of air filters currently available that use the name “HEPA.” Though both are good air filters, only one is truly capable of removing almost all types of allergens from the air. These two filters are:

• True HEPA. To qualify as a true HEPA filter, a filter must be able to remove 99.97 percent of all particles that are 0.3 microns in diameter or larger from the air. This means the filter can remove nearly all types of airborne allergens (e.g., pollen, mold) and many troublesome particles (e.g., tobacco smoke). True HEPA filters generally allow less airflow and cost more than other types of filters.
  
  
• HEPA-type. These filters often use the same kind of technology as a True HEPA, and are generally considered very good filters. However, their actual efficiency may be only 55 percent or less of particles that are 0.3 microns in diameter or larger. These filters are often much cheaper than True HEPA filters, and have a higher airflow.

There are several other types of air filters currently available for sale in the United States. Generally, HEPA filters – a type of mechanical filter – are considered the best. There are five basic types of air filters:

• Mechanical filters. These filters force air through a screen that is able to trap particles such as pollen, dander and dust mites. These filters are divided up into three different types:
  
  
• • Flat filters. Use a flat or panel filter often coated to increase particle adhesion.
    
    
  • Pleated filters. Use a filter that has been folded over to provide greater density.
    
    
  • HEPA filters. Use very fine filters to remove any particles larger than 0.3 microns.
    
    
• Electronic filters. These types of filters use electrical charges to attract and deposit particles. Many types of electronic filters use collecting places to capture the particles within the system.
  
  
• Hybrid filters. These filters use the technology of both mechanical and electronic filters to remove particles from the air.
  
  
• Gas phase filters. These filters are used to remove odors and non-particulate pollution from the air (e.g., cooking gas, gas from paints, perfumes), but do not remove any allergens from the air.
  
  
• Ozone generators. These devices produce ozone to supposedly clean the air. Neither the U.S. Environmental Protection Agency nor the American Lung Association recommends the use of these devices because high concentrations of ozone can be damaging to the lungs.

HEPA vacuum cleaners are also available. These use the HEPA filter technology to pick up particles such as dust, mold and pollen. Unlike conventional vacuum cleaners, HEPA vacuum cleaners are capable of capturing the particles and do not allow them to circulate back into the air.