Kathon CG reactivity in 1396 consecutively patch tested patients in the Copenhagen area

An update of the risk assessment for methylchloroisothiazolinone/methylisothiazolinone (MCI/MI) with focus on rinse-off products

Methylchloroisothiazolinone/methylisothiazolinone (MCI/MI) has been widely used during the last 20 years for the preservation of aqueous systems in cosmetics, toiletries and in various industrial applications. MCI/MI has a broad spectrum of activity against fungi and bacteria at very low concentrations. The allergic contact potential of MCI/MI has been known for many years. This paper provides a review of pre-clinical and clinical experimental studies as well as experience from dermatology clinics worldwide. This forms the basis for an update of the risk assessment for the use of MCI/MI in rinse-off products. The scientific data indicate that the actual sensitization rate observed with a contact allergen is extremely dependent on dose and type of exposure. This review of the data leads to the conclusion that, under normal use conditions, within the current permitted/ recommended use concentrations for MCI/MI of up to 15ppm, the risk of primary sensitization from the use of rinse-off products is negligible, and elicitation of allergic contact dermatitis in MCI/MI-sensitized individuals rare, after exposure to MCI/MI-preserved rinse-off products.

Mutagenicity of cosmetic products containing Kathon

A variety of shampoos, conditioners, skin-care lotions, and other cosmetic products contain the biocide Kathon CG, which is a mixture of two heterocyclic isothiazolinones: methylisothiazolinone and methylchloroisothiazolinone. This mixture and the related biocide, Kathon 886, have been shown to be potent sensitizers and bacterial mutagens. Five cosmetic products that list the components of Kathon on their labels and two that do not were screened for mutagenicity with Salmonella typhimurium TA100 without S-9. Five of these products and Kathon 886 were further evaluated in TA100 without and with S-9. Kathon 886, a cosmetic product that contained Kathon, and thin layer chromatography-separated components of Kathon 886 were identified by GC/MS analysis. Three of the five products that listed Kathon were direct acting mutagens with TA100. The remaining two products were considerably more toxic than the other products and could not be evaluated for mutagenicity. The addition of S-9 reduced toxicity but did not eliminate mutagenicity. The mutagenic evaluation of Kathon 886 resulted in a dose response similar to that seen with some cosmetic products but at a 1,000-fold lower concentration, and activity was also reduced by the addition of S-9 mix. S-9 reduced activity both with and without cofactors present. Thin layer chromatography separation of the components and subsequent identification by GC/MS indicated that methylisothiazolinone was nonmutagenic while methylchloroisothiazolinone was mutagenic. Additionally, a dichlorinated compound was identified which was also mutagenic. In light of these findings and the reported skin sensitization by Kathon CG in various cosmetics, we recommend that additional testing be done to assure the safety of products containing Kathon CG.

Results of routine patch testing of 834 patients in Turin

834 consecutive patients (630 female), aged between 26 and 46 years, who were suspected of having allergic contact dermatitis were patch tested with the GIRDCA standard series during 1989-1990. The most frequent sensitizers observed included nickel sulphate, cobalt, Kathon CG, perfumes, potassium dichromate and balsam of Peru. We have evaluated the influence of individual factors such as sex, age and occupation on the patch test results, and the coexistence of 2 or more unrelated but statistically significant sensitivities.

Lymphocyte transformation test for diagnosis of isothiazolinone allergy in man

The lymphocyte transformation test (LTT) has been used for evaluation of in vitro lymphocyte responses in 18 patients with dermatitis and positive patch tests to 200 ppm of a combination of 5-chloro-2-methylisothiazolinone and 28methylisothiazolinone (MCI) in nine patients with dermatitis unrelated to MCI and in seven subjects without skin diseases. Two workers sensitized by occupational exposure to a formulation containing 1,2-benzisothiazolin-3-one (BIT) were also studied. Lymphocytes from nine patch-test-positive patients proliferated vigorously to MCI in vitro. Lymphocytes from the remaining nine patients were not stimulated. Lymphocytes from two BIT-sensitized workers responded to BIT in vitro. The lymphocyte proliferation to isothiazolinones indicates the presence of memory cells in the patients' blood and confirms immunologic reaction to the inducing agent. To establish clinical relevance of LTT results, 12 MCI patch-test-positive patients underwent "use test" with lotion containing 15 ppm MCI. Four of five LTT-positive patients were use-test-positive, whereas seven of seven LTT-negative patients were use-test-negative. LTT-positive and lotion-positive patients responded to 100 ppm or lower concentrations of MCI on patch testing, whereas seven of eight LTT-negative and lotion-negative patients responded to 200 ppm only. In the case of MCI, proliferation was due to the chlorinated component, indicating that this part contains an allergenic epitope. Finally, MCI-specific lymphocyte proliferation was observed only in patients with MCI-positive skin test, but not in nine patients with dermatitis induced by other agents, or in seven subjects without skin diseases. Thus, the lymphocyte transformation test is able to distinguish between irritant and allergic skin responses. It may also be valuable in establishing the clinically relevant patch-test concentration of allergens with irritative properties.

Methylchloroisothiazolinone-methylisothiazolinone reactions in patients screened for vehicle and preservative hypersensitivity

More than 1100 patients were tested with methylchloroisothiazolinone-methylisothiazolinone, 100 ppm, in aqueous and petrolatum-based patch test materials from 1985 to 1987 by members of the North American Contact Dermatitis Group. Thirteen reactions to the aqueous materials and 10 to the petrolatum-based materials were observed. Irritant reactions were infrequent, and about half the reactions were deemed relevant. From 1984 to 1985, patch tests with this substance at a concentration of 250 ppm in petrolatum were conducted. Thirteen persons were identified as allergic, but three others were sensitized by the patch test procedure. Sensitization as not observed in tests with aqueous or petrolatum-based substance at a concentration of 100 ppm, and this concentration appears to be the best compromise between safety and sensitive detection of allergy. Use tests are helpful but not infallible as a guide in establishing relevance with methylchloroisothiazolinone-methylisothiazolinone. Wash-off products are frequently well tolerated by patients with positive reactions to this substance.

Patch test sensitivity to the preservative Kathon CG in Spain

Kathon CG is a very well studied preservative used in cosmetics and toiletries. It is effective in low concentrations (3 to 15 ppm active ingredients) and exhibits outstanding antimicrobial activity against gram-negative and gram-positive bacteria, yeasts and fungi. Although this biocide is not considered to pose a toxicological hazard at recommended use levels, the sensitizing potential of Kathon CG has been established. From November 1988 to June 1989, we patch tested 626 unselected contact dermatitis patients with Kathon CG solution containing 200 ppm active ingredients and obtained 22 (3.5%) positive reactions. Relevance was established in 7 of the 22 patients. Women were predominantly sensitized, the principal source of sensitization being cosmetics.

Kathon CG and cosmetic products

Kathon CG was determined in 156 of the most commonly used cosmetic products in Denmark. 42% of the cosmetic products were found to contain Kathon CG. Kathon CG was present in 48% of "rinse off" and 31% of "leave on" cosmetic products. The 3:1 ratio of chloromethyl isothiazolinone (CMI): methyl isothiazolinone (MI) in Kathon CG was found to be disturbed in 41% of Kathon CG preserved cosmetic products. The disturbed CMI/MI ratio was shown in 29% "rinse off" and 73% "leave on" cosmetic products. It is suggested that the chemical reaction of the ketone group of the isothizaolinones with other ingredients in cosmetic products may disturb the CMI/MI ratio of Kathon CG. The results of the study have been discussed in relation to the use of Kathon CG in cosmetic products as well as test material for allergic reaction.

Isothiazolinone preservative: cause of a continuing epidemic of cosmetic dermatitis

A preservative system for cosmetics and toiletries containing as active ingredients a mixture of methylisothiazolinone and methylchloroisothiazolinone (1.5%) is an important cause of cosmetic allergy in many European countries. Most cases have been caused by products of the "leave-on" variety, such as moisturising creams. The use of isothiazolinone preservative in such products should be abandoned. More critical evaluation of its sensitising potential before marketing might have prevented the continuing epidemic of allergic cosmetic dermatitis due to this preservative. New chemicals should undergo extensive toxicological evaluation before their use in cosmetics is allowed. Ingredient labelling should be made a legal requirement.