Molecular Diagnosis of Allergic Contact Dermatitis (SMECA).

Inclusion Criteria: * Patient, male or female, over 18 years of age. * Patient with at least one positive/doubtful patch test reaction for nickel, limonene hydroperoxide and/or linalool hydroperoxide * Patient agreeing to undergo skin biopsies and blood sampling * Patient agreeing to non-identifying pictures being taken of lesions * Patient available to carry out skin tests and their interpretation * Patient affiliated to or benefiting from a social security regime * Patient having been informed and having signed a written, free and informed consent. Exclusion Criteria: * Patient with active dermatitis lesions on the forearm * Patient with a history of allergic reaction to a local anesthetic product * Patient with wound healing disorders (hypertrophic or keloids scars) * Patient with hematological disorders * Patient having topical treatments with corticosteroids or immunomodulators on the forearms during the 21 days prior to the start of the study * Patient having had excessive exposure to ultraviolet during the 21 days prior to the start of the study. * Patient on systemic corticosteroid therapy, immunosuppressants or biological therapy. * Patient whose follow-up is impossible for reasons psychological or geographical. * Patient taking part in another clinical study * Protected patient: adult under guardianship, curatorship or other legal protection, deprived of liberty by judicial or administrative decision * Pregnant, breast-feeding or parturient woman