Irritation is Multidimensional Severe irritation is easy to detect. Visual signs such as erthythema and edema are obvious.
Subjects report burning, stinging and pain.
Objective electronic measures of irritation such as conductance, temperature and local blood flow show clear differentiation between irritated and non-irritated sites. Simply stated, as the intensity of irritation increases, irritation can be detected easily by any number of measures. The problem lies with irritation of lesser intensity. Very mild irritation can be reported subjectively, but most objective measures are unable to clearly reflect the experience. Erythema is absent, so any measures which reflect changes in blood flow won't correspond with the subjective experience of very mild irritation.