Between October 1986 and June 1987 we patch tested 420 patients with Kathon CG at 100 ppm and obtained 23 positive reactions (5.5%). The other 5 Swiss university clinics joined our study between January and June 1987 and obtained sensitization rates ranging from 0.7 to 7.5%. The total mean value including Geneva was 3.6%. We did threshold patch testing in 12 patients with the following Kathon CG dilutions: 100, 50, 25, 15 and 7 ppm. We observed progressively diminishing skin reactions, especially below 25 ppm, but we still obtained slight positive reactions in 2 patients with Kathon CG at 7 ppm. Those reactions were relevant because the dermatitis disappeared when the use of Kathon-containing creams was discontinued.

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The rate of sensitization to isothiazolinones (Kathon® CG) detected in Switzerland rose from 3.5% (out of 2,491 patients) in 1987 to 6.3% (out of 982 patients) in 1988 and 5.6% (out of 2,295 patients) in 1989–90. This rate of sensitization appears to be related to the more and more widespread use of isothiazolinone biocide in cosmetics, domestic products and in industry.

PRECÍSSources of nickel allergy can be missed, as in our unusual case of contact dermatitis to nickel. DISCUSSIONA 31-year-old physicist presented to our clinic with an 8-week history of erythematous and itchy plaques on his wedding ring finger and on his belly, behind his belt buckle. He was in good health with a history of atopic dermatitis and allergic rhinitis.Patch tests were performed with the European standard series (Hermal; Reinbek, Germany) and preservatives series. The readings were done on days 2 and 4. On days 2 and 4, the reading was positive (+++) to nickel(II) sulfate. The test confirmed contact dermatitis to nickel.The patient changed his belts, and improvement was noted on his aforementioned abdominal skin. This was not the case for his finger. Later it was discovered that his ring was made out of a type of meteorite iron called Gibeon, which was bought from a specialized boutique in Paris, France.Dimethylglyoxime test (Chemotechnique Diagnostics, Vellinge, Sweden) was done to identify the presence of nickel in his ring, and the result was positive.The dermatitis resolved once he stopped wearing his ring and avoided contact with objects containing nickel.

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