Contact allergy to Kathon® CG. 35 cases out of 977 patients studied

Abstract

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. Repeated open application tests (ROAT) using a 15 ppm cream applied onto the forearm versus excipient alone were performed in 15 patients and gave good correlations in 10. HPL chromatography was used to detect Kathon® CG in various suspicious cosmetics. Kathon® CG was found in a cosmetic for eyelids where it should not have been according to the EEC directives. The relationship between positive patch test and use of Kathon® CG-containing cosmetics was certain in 8 cases, probable in 10 cases, doubtful in 8 cases and uncontrolled in 9 cases. Cosmetics (especially those of the leave on type) were most frequently involved, a rinse off product (shampoo) was incriminated in one case (20). Derivatives of Kathon® CG used in industrial products with various trade-names are recognized as being allergenic. Our case No. 16 was positive to benzisothiazolinone (BIT) 0.05 p. 100 in alcohol and cross-reacted to Kathon® CO; the product incriminated was a glue containing BIT, and only the hands were involved. We conclude that Kathon® CG cannot be recommended as antimicrobial agent not only in leave on but also in rinse off cosmetics because of its allergenic frequency (3.6 p. 100 in our study).