Usefulness of Patch Testing With Patient's Own Products in the Diagnosis of Allergic Contact Dermatitis

BACKGROUND: The usefulness of using patient's own products in patch tests for the diagnosis of allergic contact eczema is well known. However, most of the literature is based on case series published decades ago, and they are focused on cosmetics and fragrances. OBJECTIVE: The aim of the study was to evaluate the usefulness of using patient's own products in patch tests for the diagnosis of contact eczema in a contact dermatitis unit, describing the most frequently positive own products, as well as the most frequently responsible allergens. METHODS: In a 17-year period, 3514 patients were patch tested in our department. In 2429 patients, patch testing with the patients' own products was performed. RESULTS: We found that 363 patients (10.33%) reacted to their own products. In 131 cases (3.81%), reacting to their own product was the only clue for detecting the responsible allergen for allergic contact eczema. Most reactions were found for topical medications, moisturizers, and adhesives. Fragrance mix I, methylchloroisothiazolinone/methylisothiazolinone, ketoprofen, and colophony were found to be the allergens most often responsible. CONCLUSIONS: It is essential to include patient's own products in the study of allergic contact eczema to make a correct diagnosis. In our series, 3.81% of the patients would not have been correctly diagnosed if their own products had not been included in patch tests.