described three mechanisms by
which ambient odors might elicit health symptoms: (1) exposure
to odorous compounds elicits a response in the trigeminal nerve
system referred to as an irritation effect (irritation causes the
health symptoms, whereas odor is the exposure marker); (2) at
nonirritant concentrations exposure elicits an innate, learned aversion;
(3) copollutants (such as endotoxin) elicit a health symptom
response. They note that objective bio-markers of health symptoms
are needed, to determine if and when health complaints constitute
health effects. For these reasons, measurements of volatile
An additional factor that complicates the situation is that odorous compounds, even when individually present below their irritant threshold concentrations, can when present in mixtures collectively exceed an irritant threshold concentration and thus elicit a response in a sensitive receptor