Steinemann AC. Fragranced consumer products and undisclosed ingredients. Environ Impact Asses Rev (2008), doi:10.1016/j.eiar.2008.05.002. http://www.ce.washington.edu/people/faculty/bios/documents/Steinemann2008.pdf
'What the Nose Knows' by Avery Gilbert: An olfactory specialist looks at the smelly side of life
There he examines the syndrome known as Multiple Chemical Sensitivity or Idiopathic Environmental Intolerance.
The verdict: The symptoms are real but psychosomatic. "The psychogenic hypothesis doesn't sit well with some IEI patients ... [T]hey resent any suggestion that ... implies their suffering isn't real. The good news for them, if they will only hear it, is that the psychogenic hypothesis points to a treatment."