[Contact hypersensitivity to Kathon CG. Apropos of 35 cases among 977 tested subjects].

Kathon CG (Rohm and Haas) is a mixture of two isothiazolinones: chloromethylisothiazolinone and methylisothiazolinone. It is widely used in aqueous solution as antimicrobial agent in cosmetics (CG means cosmetic grade) instead of parabens. Routine testing is effected with Kathon CG in aqueous solution at 100 ppm (Trolab) in finn chamber tests on scanpor (ICDRG directives). Between September 1987 and September 1989, 977 patients (538 women, 439 men) referred for suspected contact allergy were tested. Thirty-five patients (77 p. 100 of whom were young women) with a history of allergy to cosmetics were found to be positive. Face, hands or both were involved in 15, 7 and 9 cases respectively, and a lupus-like reaction was observed in one patient. Our results (frequency: 3.6 p. 100) were compared with previously published results ranging from 0.67 p. 100 to 16.1 p. 100 (tables IV and V). Such wide variations can be explained by different selections of patients, different uses of cosmetics and lack of standardization in testing. Patch tests were strongly positive (quoted + +) in all cases. None of the irritant effects previously reported (3, 8, 28) was detected. In a control study carried out two months later, diluted patch tests (100, 50, 25, 15 and 7.5 ppm) were performed in 15 patients and were positive in 11 of them: 5 at 25 ppm, 1 at 15 ppm and 5 only at 100 ppm. Contrary to previous suggestions (7, 28, 36), there was no correlation between allergenic potential and minimal concentration, so that the "no response concentration" concept could not be confirmed.(ABSTRACT TRUNCATED AT 250 WORDS)