Evidence or no Evidence
"I think we should look for some hard evidence in this case..." A&C
This is a tricky one. The vested interests always say "there's no evidence..etc" and it is difficult to prove, esp if you rely on hard controlled trial scientific standards.
The same was true for BSE & the "no evidence" get out was used to great effect by the government.
There is a huge amount of anecdotal and other evidence around and several hundred aircrew (cabin & FD) have no doubt they've been affected. As a result, the Aerotoxic Assn (there's loads more info on their website) has been formed to address the issue. This is a big problem, with some types being constant offenders & a/c age seemingly an influence.
Proving it isn't so easy, especially when those responsible for oil emissions into cabin air, are staring huge issues in the face if they do so.
As a retired pilot I'm now only exposed when I fly as a passenger but I know one or two ordinary members of the public who've experienced the classic symptoms after flying but they had no idea what they were linked to. My guess is that there's thousands out there who simply don't realise what they've ingested.