The preservative Kathon CG is a commercial preparation, consisting of 2 active ingredients and other components. 28 patients with contact allergy to Kathon CG participated in a study in which patch testing was performed with serial dilutions, and with 5 chromatographically separated fractions. All reacted to fraction IV, and 2 patients also to fraction II. Mass spectrometry and nuclear magnetic resonance spectrometry identified fraction II and IV to be the active ingredients; 2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one.

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Of 976 patients routinely patch tested with Kathon CG (Rohm & Haas), 300 ppm, 43 (4.4%) gave a positive reaction. Of 170 patients routinely tested with Kathon CG 250 ppm, 10 (5.9%) gave a positive reaction. Out of 34 patients tested with serial dilutions of Kathon CG, 17 (50%) reacted to 100 ppm, 8 to 30 ppm and 2 to 10 ppm. The concentration of 1000 ppm of Kathon CG was irritant in some cases, but 300 ppm was not irritant. Of the 976 patients tested with Kathon CG 300 ppm, 8 (0.8%) showed a "flare-up" reaction, indicating patch test sensitization. Of the 170 tested with Kathon CG 250 ppm, 2 (1.2%) were sensitized. When the patch-test-sensitized patients were retested with serial dilutions, they showed the same pattern as the other patients. 13 sensitized patients were use tested and 7 (54%) gave responses. In the literature, Kathon CG 100 ppm is recommended as the routine patch test concentration. However, 50% of the sensitive persons may then be overlooked. In our clinics, Kathon CG has become the second most common contact sensitizer, but the sensitivity cannot be traced in all patients with clinically relevant allergy without an unacceptable risk of patch test sensitization.

Atranorin, one of the most common lichen substances, gave positive patch test reactions in eight subjects (1%) in a routine series. These subjects also reacted to fumarprotocetraric acid and some of them to evernic acid. Stictic acid and usnic acid gave negative reactions. The lichen oak moss Evernia prunastri and an oak moss perfume gave positive reactions. Thin-layer chromatography and a spot test indicated that atranorin is present in oak moss perfumes which are made from oak moss and tree moss. Contact with oak moss perfumes and lichens in nature may cause atranorin allergy. None of the eight subjects had a history of light sensitivity or atopy and none had chronic facial eczema.

Six patients developed dermatitis while working with ultraviolet curing inks in four different printing plants. Contact allergy was found to the multifunctional acrylate monomers pentaerythritol triacrylate (PETA) and trimethylol propane triacrylate (TMPTA) and to the epoxy acrylate and polyesteracrylate prepolymers.