I think that the primary cause of aerotoxic syndrome is not to do with fumes from outside, but burnt oil that gets into the air conditioning giving the "sweaty sock" smell familiar to many who have operated the types notorious for it.
Having flown such a type for over twenty years and experienced the smell briefly on very many occasions and had "fume events" a few times I now have many of the symptoms described in aerotoxic syndrome.
The symptoms are often the same as those experienced by farming organophosphate exposure, which is unsurprising as the oils contain the same chemicals.
The problem is that all this is very difficult to scientifically prove, though I do remember some measurements being taken many years ago in affected aircraft which must have proved the presence of fumes but which nothing was ever heard of.