[Gibbon1]

I think they can also collect enough organic matter for mold to start growing on the downstream side. I base that on pictures of automotive cabin filters that are revolting.

[sizzle]

Would some generous Lysol spray get rid of the mold?

[AstralStorm]

Yes, but it will ruin dust filtration, so the proper choice is hot water vapor, dry heat, or hydrogen peroxide. Perhaps silver ions too.

HEPA filters use exactly the same meltblown fabrics as respirators, except thicker and in accordion form.

[Gibbon1]

Just flip it around