Practical Advice to Correctly Perform Patch Test

Abstract

Allergic contact dermatitis corresponds to an inflammatory reaction caused by contact with an external agent. It is a reaction mediated by a type IV hypersensitivity mechanism or delayed, and requires prior sensitization of the individual. Patch testing is the gold standard method for the diagnosis of allergic contact dermatitis. It is the in vivo proof of the effect caused by contact with the allergen, and evokes on a small scale the elicitation phase of a delayed hypersensitivity reaction. The patch test is not a complex procedure; however, its success depends on different factors that include an appropriate assessment of the patient considering the different sources of exposure to possible allergens, the correct technique of placement of the patches, and the necessary knowledge to properly interpret the results and determine their relevance. The objective of this review is to provide a series of general recommendations to adequately perform this test, and so the results are reliable and allow proper management of the patient. Although used for more than 120 years, the patch test procedure is performed with variability around the world. Although the procedure is broadly similar to the original method, it is not uncommon to observe differences in the results reported by the different observers. This may be influenced, among other factors, for differences in the methodology used by the physician who perform it. There are numerous potential points for error that the physician must keep in mind. Although during the last decades great efforts have been devoted to the optimization and standardization of the materials and the methodology, physicians’ knowledge and experience are fundamental for the reliability of the results and the benefits from this test.