HEPA filters need to be cleaned regularly. Both HEPA room air purifiers and HEPA vacuum cleaners need to have their filters changed (or cleaned on some types) when they are dirty to continue to function properly. How often they need to be changed depends on several different factors, such as:

• How often the filter is used. Filters that are used frequently will need to be changed (or cleaned) more often than those that are used only occasionally.
  
  
• Whether a prefilter is used. A prefilter is available on some models and works to stop many of the larger particles from reaching the main HEPA filter. The prefilters can often be cleaned and should allow the main HEPA filter to last longer.
  
  
• The kind of environment in which the filter is being used. Environments with molds, pets or tobacco smokers will usually require filter changes more often.

Individuals with allergies or asthma who use a HEPA vacuum cleaner should take care when cleaning the filter. It is a good idea to change the bag when it is about one-half full, and to change the bag outdoors, if possible. This keeps the dust that inevitably escapes from the bag during changing out of the house. Individuals who are highly allergic should wear a mask during the changing procedure.

In addition, studies have shown that vacuuming with a HEPA vacuum cleaner can temporarily increase the amount of allergens in the air as the cleaning process stirs up particles. It is a good idea for allergic individuals to wear a mask when cleaning or, if possible, have someone else clean for them.