Contact dermatitis and diagnostic techniques.

Proper use of patch testing to identify the causes of contact dermatitis requires that the physician use the test where it will have the highest likelihood of benefit. Identifying endogenous dermatoses by morphologic and historical criteria and distinguishing these from likely cases of exogenous dermatoses prior to testing will enhance the number of people helped by applying the patch test procedure. Knowledge of the technical aspects of patch testing and how to instruct patients with positive and negative tests is an essential part of solving complex contact dermatitis problems.