Reading of Patchtest Reactions
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The scrupulous reading of the patch test reactions must be made by using a magnifying glass, carrying out digital palpation, and assessing symptoms. Allergic test reaction is characterized by itching, erythema, papules, and vesicles; generally there is also a reaction outside the area where the test substance has been applied. After making qualitative-quantitative assessment, positive reactions are classified according to well-established criteria. Positive allergic reactions must be differentiated from false-positive results. The possibility of false-negative results and mixed (irritant and allergic) and doubtful reactions must be considered. Patch and photopatch testing can involve some side effects.