The smallest of pollen grains (~0.6 microns) and other allergens should be trapped by a HEPA filter, however what happens when these decay / break apart? Is the allergen the whole pollen grain or are the allergens really the proteins that make up the grain (which by themselves would be too small for the filter to hold)?

Just wondering because the measures I implemented a couple of months ago (air purifier + a window screen made of polypropylene) seem to have been effective at first, but now it seems to be worse in the "controlled environment" than elsewhere. It's difficult to say for sure, but I was wondering if this theory holds any weight. Could it be that the various allergens trapped in the screen and air purifier are now breaking down and passing through the filtration?

The closest thing to an answer I could find is this:


  • Immunisation treatment of allergies introduces allergen components into the patient and presumably these are much smaller than the whole pollen grain. – lm713 May 25 '17 at 12:42
  • However, HEPA filters can actually be very effective at trapping particles smaller than 0.3 microns. The 0.3 microns size is actually a weak point for HEPA filtration which is why it is tested for the classification of the filter (source link). What happens to these particles as they decompose and whether components are eventually ejected is still a mystery to me. – lm713 May 25 '17 at 12:51
  • I saw a HEPA air purifier that included a layer to neutralise allergens. I am not sure whether it utilised polyphenols (as in some car cabin air filters) or by some other process. This suggests the manufacturer believed it to be beneficial to neutralise allergens despite HEPA filtration. Unfortunately I cannot find it any more. I do remember it was made by a large global manufacturer, which makes it even more frustrating :-) – lm713 May 25 '17 at 12:56

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