Molecular Diagnosis of Allergic Contact Dermatitis (SMECA).

A blood sample (48 ml) will be collected from each patient before performing the ROAT tests. This sample will be used to perform in vitro lymphocyte proliferation test, and cytokine measurements.

2 skin biopsies will be performed at the inclusion: one from positive/doubtful patch test reaction and one from control patch test. In case of positive ROAT test, 2 additional biopsies will be collected: one from positive ROAT test reaction and one from control area. Molecular analysis will be performed.

ROAT test (repeated open application test) is a use test used to establish the clinical relevance of patch tests. Patients will be exposed to 3 solutions of increasing concentration containing the culprit allergen (nickel, limonene hydroperoxide or linalool hydroperoxide), as well as a solution containing the vehicle alone (control solution), 2 times a day for up to 21 days, in the absence of a reaction.