I think Java Dreaming, that some are more susceptible than others to chemicals and fumes. After nearly forty years of flying, I have had no ill effects, and have flown everything from the DC3 to the B747. I don't know any older pilots that have ever been affected by fumes, but that is not to say it happens. Unfortunately some people have systems that seem to develop allergies, and react, when others inhaling the same stuff, have no side effects at all. The whole world seems to suffer allergies now, that were unheard of even twenty years ago, why? Who knows.