This is beneficial sufferers, because the HEPA filter traps the fine particles which trigger allergy and asthma symptoms. For a HEPA filter in a vacuum cleaner to be effective, the vacuum cleaner must be designed so that all the air drawn into the machine therapure air purifier is expelled through the filter, with none of the air leaking past it. This is often referred to as “Sealed HEPA” or sometimes the more vague “True HEPA”. Vacuum cleaners simply labeled “HEPA” may have a HEPA filter, but not all air necessarily passes through it. Finally, vacuum cleaner filters marketed as “HEPA-like” will typically use a filter of a similar construction to HEPA.