Is inhaling dust very harmful to your health? Such as, if I am
cleaning out an old box and a puff of dust comes out into the air, and
I continue working (probably inhaling the dust as well) then is this
very, very harmful/dangerous to me? Or, just exactly how harmful IS it
to me and my body? And will it get into my eyes and do something to
that as well?

Thanks!

Humans have been around for 1000's and 1000's of years.  Humans now
live longer than at any time.  So I think inhaling handfuls of dust
will not hurt you - let alone the small amount you have done by
opening an old box.

Think of it this way, you'd have to smoke cig. for 20 to 30 years in
order to get cancer.  Try working in a coal mine, steel mill, cement
plant - now those are dirty - dusty jobs.  Doing a little spring
cleaning does not measure up to the carp those people inhale.

So breath deep - and enjoy the treasues you might find in those old boxes!