Methylchloroisothiazolinone/methylisothiazolinone and methylisothiazolinone hypersensitivity in 1122 patients: A national multicenter study organized by the Hungarian Contact Dermatitis Group

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The preservative Kathon CG, containing chloromethylisothiazolinone (MCI) and methylisothiazolinone (MI) in a 3:1 ratio, has been widely used because of its antimicrobial effectiveness. Its sensitizing effect in cosmetics is documented since 1985,1 later confirmed by European studies finding average sensitization prevalences of 3%.2-4 MI alone was introduced as a preservative at the beginning of the 21st century for industrial and later for cosmetic use. An epidemic of MI sensitization in Europe, the USA, and Asia with various clinical symptoms has been reported. Among the products causing MI hypersensitivity, cosmetics are most important, including hair care products.5-15 Because MI constitutes only 25% of the total MCI/MI test material, the earlier prevalence of hypersensitivity to MI cannot be determined exactly by MCI/MI routinely tested in the baseline patch series: for instance, MCI/MI did not detect 27.3% of MI allergy in a previous study.8 For this reason, inclusion of MI in the baseline patch test series was recommended, using MI 2000 ppm (0.2%) aq.16, 17 The Hungarian Contact Dermatitis Group patch tested MI 0.2% aq. (allergEAZE, Brial allergen, Germany) between January 2015 and January 2016 along the standard environmental allergen series (allergEAZE), thus simultaneously with MCI/MI 0.01% aq. In six dermatological centers in Hungary, 1122 patients were tested prospectively. The haptens were applied on the back and occluded for 48 h. Evaluation of the test was performed 1 h after ending occlusion, and on day (D) 2, and on D3, D4, and D7. Reactions were regarded as positive if + or stronger. Exclusion criteria for the patch tests were medication with local steroids 1 week prior to the examination, taking antihistamines 1 week prior to and during the examination, or undergoing systemic steroid treatment, received ultraviolet radiation 6 weeks prior to the examination, or presence of acute or active skin symptoms, active rhinitis, pregnancy, and lactation. The mean age of the tested patients was 47 years (13-92 years). There were 268 men (mean age: 48.5 years, age range: 14-84 years) and 854 women (mean age: 46.5 years, age range: 13-92 years). Overall, 28/1122 (2.5%) patients were sensitized only to MI with a mean age of 42.4 years (17-76 years), including five males (mean age: 48.6 years, age range: 40-58 years) and 23 females (mean age: 41.1 years; age range: 17-76 years). In comparison, 18 patients were sensitized solely to MCI/MI (1.6%) with a mean age of 51.7 years (22-75 years), including two men (51 and 53 years respectively) and 16 women (mean age: 51.7 years, age range: 22-75 years). Finally, concomitant MI and MCI/MI sensitization was found in 36 patients (3.2%) with a mean age of 49.8 years (22-77 years): seven men (mean age: 51.3 years, age range: 32-75 years) and 29 women (average: 49.8 years, age range: 21-77 years). Thus, in total, there were 82 (7.3%) patients sensitized to MI and/or MCI/MI and the frequency of MI sensitization was 5.7% (64 patients). An immediate reaction appeared after 60 min only in one patient 1 h after ending occlusion. Irritant reactions were seen for both MI alone and MCI/MI in five patients each (0.4%). Among the sensitized patients, allergic contact dermatitis was found most frequently (Table 1). In a few cases sensitization was not clinically relevant, and atopic dermatitis and stasis dermatitis were diagnosed. Skin symptoms were localized typically on the hands, face and eyelids, and the trunk. Generalized symptoms were observed only in MI-sensitized patients (6.2%; Figure S1). According to the MOAHLFA index, hand and face dermatitis was common (Table S1). Among the sensitizing products, shower gels and liquid soaps, hair shampoos, moist cleaning wipes, and household products were the most common (Table 2). Concomitant sensitization to fragrance mix I and II, wood tar mix, and Myroxylon pereirae (balsam of Peru) was seen, possibly explained by fragrances used in the same products (Table S2). Concerning occupational allergens, we detected MI sensitization in two patients, and concomitant MCI/MI and MI sensitization in four of these patients. The sources of allergens in these patients were mostly liquid soaps used at their workplace (Table S3). The Hungarian Contact Dermatitis Group evaluated the test results of 1122 patients from six dermatological centers obtained during 1 year. A clinical study in Hungary,18 performed at the Department of Dermatology, Venerology and Dermato-Oncology of Semmelweis University, showed a prevalence of MI hypersensitivity of 4.8%. Our present national result of MI sensitization (5.7%) fits to the European data,19-30 albeit on the lower end. Our patients are predominantly female and affected mostly in their 40s. The clinical symptoms appeared mainly on the patients' hands and face. The most frequent provoking products were liquid shower gels and soaps, shampoos, and household products. According to our data, MI sensitization is associated typically with multiple contact hypersensitivities, mostly with fragrances. This confirms the former experience that MI allergy is a risk factor in the development of polysensitization. This observation and the possibility of cross-reactions between MI, MCI, and other isothiazolinones render this topic important also in the future.31-35 The authors declare no conflict of interests. Figure S1 Localization of skin symptoms by patients sensitized to MI and/or MCI/MI Table S1. Distribution of MI- and/or MCI/MI-sensitive patients (+n = 82) according to the MOAHLFA index (percent of positive reactions) Table S2. Associated hypersensitivities by each patients sensitised to MI and/or MCI/MI Table S3. Occupational dermatitis in patients sensitized to MI and/or MCI/MI (n = 12, M: male, F: female) Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

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