Outside Loop --
You are being a little simplistic (and not a little insensitive) in suggesting that persons with chemical intolerances not pusue aviation, nor indeed engineering careers.
How would you go at answering these questions...
1. At what point in your life do you predict that you will suffer from arthritis, if at all?
2. From heart disease?
3. From mature onset diabetes?
4. Did you personally guarantee to your employer that you would not suffer an injury in a motor vehicle or sporting accident that will limit your ability to operate as a flight crew member?
5. Can you positively state that you have never lived nor worked nor visited a building of any sorth that possibly had asbestos materials?
My point being, that your requirement is ridiculous. Very few people know for sure what it is that will kill them or possibly affect them in later life. None of the people suffering from "146 fumes" would have expected that outcome when they signed on. And no-one can yet say which particular chemical intolerance it is that some 146 personnel are suffering from.
Moreover, most pilots would be hoping to have about a 40 year aviation career. I am 7 years in, so the aeroplane that I will be flying just before I retire is possibly not yet on the drawing board. Who knows what electrical/hydraulic/etc systems it will use? Should I disqualify myself now, just in case I may find that a new HUD system installed 10 years from now may cause mild diahorreah?