Recommendation to include methylisothiazolinone in the European baseline patch test series - on behalf of the European Society of Contact Dermatitis and the European Environmental and Contact Dermatitis Research Group

Cosmetovigilance for infrequent allergens in Spain using a national online registry: The example of allergic contact dermatitis caused by phenylethyl resorcinol

BACKGROUND

Monitoring of adverse events induced by cosmetics performed by health authorities, known as cosmetovigilance, has been relied on the collection of case notifications.

OBJECTIVES

We aimed to show how a contact dermatitis registry can contribute to the cosmetovigilance of emerging allergens. We used the example of phenylethyl resorcinol, an infrequent allergen with only 6 previous cases reported in Europe and Japan since 2013.

METHODS

A systematic search in the Spanish Registry of Contact Dermatitis and Cutaneous Allergy (REIDAC) database was performed to identify patients with positive patch test to phenylethyl resorcinol or cosmetics that contains it between June 2018 and January 2023. We collected the main clinical features of these patients and compared them with those of patients recorded in the registry with similar epidemiological features.

RESULTS

Thirteen patients with positive patch test to phenylethyl resorcinol were identified. All the patients were women with a mean age of 42 years (range 32-59) and their lesions were mainly in the face.

CONCLUSION

Assessing the importance of infrequent allergens based solely on a case series is difficult. Multicentre registries facilitate the collection of cases and provide appropriate background information for new allergens.

Effects of aluminium chloride added to common patch test substances

BACKGROUND

A modulating effect of aluminium regarding type IV reactions might exist but has not been further investigated.

OBJECTIVES

The aim of this study was to investigate the effect on patch test reactions when adding aluminium chloride hexahydrate (Al-Cl) to common test preparations.

MATERIALS AND METHODS

Al-Cl in different concentrations was added to nickel sulphate 15.0% aqua (Ni), methylisothiazolinone 0.2% aqua (MI) and fragrance mix I 10.0% aqua/ethanol (FM I). The Ni preparations were tested in 120 consecutive patients. MI and FM I were tested in participants known to have contact allergy to the respective allergen. McNemar's test was used to decide which Ni preparation had the highest sensitivity. Wilcoxon signed-rank test was used to calculate pairwise comparison in summarized test score for the preparations with MI and FM I.

RESULTS

Adding Al-Cl 20.0%/30.0% to Ni identified twice as many patients with contact allergy to nickel compared to Ni without Al-Cl. Adding Al-Cl 20.0%/10.0% to MI, decreased the patch test reactivity compared to MI without Al-Cl. No differences in patch reactivity were noticed when adding Al-Cl to FM I.

CONCLUSION

Al-Cl 20.0% or 30.0% seems to enhance the patch test reactivity to Ni 15.0% aqua.

Patch test results in a Dutch paediatric population with suspected contact allergy: A retrospective cohort study

BACKGROUND

Allergic contact dermatitis (ACD) in paediatric patients is on the rise. Continuous identification of emerging allergens is of great importance to ensure accurate patch testing.

OBJECTIVES

To assess the frequency and relevance of contact sensitivity in children and adolescents and evaluate changes in sensitization rates in the last decade.

METHODS

All patients with suspected ACD who underwent patch testing at the Amsterdam University Medical Centers between 2015 and 2021 were included.

RESULTS

Of 439 patients tested with the European Baseline Series (EBS) and additional series, 334 (76%) patients had at least 1 positive reaction and 172 patients (39%) had 1 or more relevant positive reactions. If additional series would have been omitted, 20% of patients would have been underdiagnosed. Compared to patients tested between 1996 and 2013, reactions to metal allergens, isothiazolinones, methyldibromo glutaronitrile, carba mix, amerchol L-101, and benzophenone-4 were more frequently observed.

CONCLUSIONS

This study confirms the need for patch testing in paediatric patients suspected of having ACD. For accurate patch testing, it is advised to include additional series.

Demographic and clinical profile of occupational cases of sensitization to methylisothiazolinone and Kathon CG: a cross-sectional study

Abstract Introduction: methylisothiazolinone alone or associated with methylchloroisothiazolinone (Kathon CG) is a preservative related to occupational allergic contact dermatitis. Objectives: to evaluate the demographic and clinical profile of occupational cases of sensitization to isothiazolinones in the city of Rio de Janeiro and to describe the presence of these preservatives in national paints. Methods: cross-sectional study based on information from medical records of workers who underwent patch testing between 2013-2017. The prevalence of clinical, demographic and occupational characteristics was described and an unadjusted model was used to investigate the association between variables. We sought the presence and concentration of isothiazolinones in the chemical composition sheets of national paints. Results: among the 768 workers submitted to the tests, 68 had occupational dermatosis with a positive result for sensitization to methylisothiazolinone/Kathon CG. The most affected occupations were those related to domestic activities and cleaning. There was a greater likelihood of sensitization to isothiazolinones in women and in those with involvement of the hands and legs. Among the 61 paints evaluated, 26 had some isothiazolinone, with methylchloroisothiazolinone being the most common. Conclusions: sensitization to isothiazolinones can impact workers’ health and demands greater vigilance on cleaning materials and cosmetics, as well as discussing the composition regulation of the paints sold in Brazil.

Perfil demográfico e clínico de casos ocupacionais de sensibilização a metilisotiazolinona e Kathon CG: estudo seccional

Resumo Introdução: a metilisotiazolinona isolada ou associada à metilcloroisotiazolinona (Kathon CG) é um conservante relacionado à dermatite de contato alérgica ocupacional. Objetivos: avaliar o perfil demográfico e clínico dos casos ocupacionais de sensibilização a isotiazolinonas no município do Rio de Janeiro e descrever a presença desses preservativos em tintas nacionais. Métodos: estudo transversal baseado em informações de prontuários de trabalhadores submetidos a testes de contato entre 2013-2017. Descreveu-se a prevalência de características clínicas, demográficas e ocupacionais e utilizou-se um modelo não-ajustado para investigar a associação entre variáveis. Buscou-se a presença e a concentração de isotiazolinonas nas fichas de composição química de tintas nacionais. Resultados: dentre os 768 trabalhadores submetidos aos testes, 68 apresentavam dermatose ocupacional com resultado positivo para sensibilização à metilisotiazolinona/Kathon CG. As profissões mais acometidas foram as relacionadas a atividades domésticas e limpeza. Houve maior chance de sensibilização às isotiazolinonas nas mulheres e naqueles com acometimento das mãos e das pernas. Entre as 61 tintas avaliadas, 26 possuíam alguma isotiazolinona, sendo a metilcloroisotiazolinona a mais comum. Conclusões: a sensibilização às isotiazolinonas pode impactar a saúde do trabalhador e demanda maior vigilância com materiais de limpeza e cosméticos, assim como a discussão da regulação da composição de tintas comercializadas no país.

Evolution of methylisothiazolinone sensitization: a Belgian multicentric study from 2014 to 2019

BACKGROUND

In the 2010s an epidemic of allergic contact dermatitis to methylisothiazolinone occurred in Europe. European authorities banned the use of methylisothiazolinone in leave-on cosmetics in 2017 and limited its use in rinse-off products in 2018.

OBJECTIVES

To investigate the sensitization rate to methylisothiazolinone in Belgium between January 2014 and December 2019, and to assess co-sensitizations to octylisothiazolinone and benzisothiazolinone in methylisothiazolinone -sensitized patients.

METHODS

A retrospective study of patch test results with methylisothiazolinone, octylisothiazolinone and benzisothiazolinone observed in patients attending five Belgian hospitals.

RESULTS

Overall, 560 of 10.029 patients (5.58%) had a positive patch test reaction to methylisothiazolinone, and its sensitization rate decreased from 7.9% in 2014 to 3.1% in 2019. Rinse-off cosmetics, paints and detergents were the most prevalent sensitization sources in recent years. Simultaneous reactions readily occurred to octylisothiazolinone, and, surprisingly, and increasingly, also to benzisothiazolinone.

CONCLUSIONS

Contact allergy to methylisothiazolinone in Belgium has reached a pre-epidemic level, reflecting the impact of recent regulatory measures. Leave-on cosmetics, in contrast to rinse-off products, have almost disappeared as sensitization sources in Europe. Paints and detergents also remain problematic. The remarkably high number of patients (co-) sensitized to benzisothiazolinone should be a focus of future research. This article is protected by copyright. All rights reserved.

Further Evidence of Allergic Contact Dermatitis Caused by 2,2'-Methylenebis(6-tert-Butyl-4-Methylphenol) Monoacrylate, a New Sensitizer in the Dexcom G6 Glucose Sensor

BACKGROUND

Since the spring of 2020, we have seen several patients experiencing severe allergic contact dermatitis (ACD) from the Dexcom G6 glucose sensor after the composition of the sensor's adhesive patch had been changed. We have previously reported the finding of a new sensitizer, 2,2'-methylenebis(6-tert-butyl-4-methylphenol) monoacrylate, in the Dexcom G6 adhesive patch. Three patients with ACD from Dexcom G6 tested positive to this sensitizer. They were also allergic to isobornyl acrylate, a sensitizer present both in Dexcom G6 and in other medical devices previously used by these patients.

OBJECTIVE

The aim of the study was to report the first 4 cases sensitized to 2,2'-methylenebis(6-tert-butyl-4-methylphenol) monoacrylate without a simultaneous allergy to isobornyl acrylate.

METHODS

The cases were patch tested their own materials, a medical device series, and 2,2'-methylenebis(6-tert-butyl-4-methylphenol) monoacrylate in several concentrations.

RESULTS

All 4 cases tested positive to 2,2'-methylenebis(6-tert-butyl-4-methylphenol) monoacrylate at either 1.0% or 1.5% in petrolatum, whereas 20 controls tested negative to both concentrations.

CONCLUSIONS

The cases reported here provide further evidence of 2,2'-methylenebis(6-tert-butyl-4-methylphenol) monoacrylate as a relevant culprit sensitizer in patients with ACD from Dexcom G6. However, the initially used patch test concentration (0.3%) did not suffice to elicit positive reactions in these cases, which is why patch testing at 1.5% is recommended.

Patch Testing With Methylchloroisothiazolinone/Methylisothiazolinone Using a New Diagnostic Mix-A Multicenter Study From the International Contact Dermatitis Research Group

BACKGROUND

In the early 1980s, a preservative containing a mixture of methylchloroisothiazolinone (MCI) and methylisothiazolinone (MI) in a ratio of 3:1 was introduced. This mixture (mix) has been patch tested at 100 ppm (0.01%) worldwide and at 200 ppm (0.02%) in Sweden since 1986 and also in the European baseline series since 2014.

OBJECTIVE

A new aqueous mix of MCI 0.015% and MI 0.2% was compared with patch testing with the 2 aqueous baseline preparations of MCI/MI 0.02% and MI 0.2%.

METHODS

Four thousand three hundred ninety-seven patients with dermatitis in 12 International Contact Dermatitis Research Group dermatology departments from 3 continents were patch tested simultaneously with the 3 preparations.

RESULTS

The frequency of positive patch tests to the allergens varied between 0% and 26.7% in the 12 test centers. The new mixture MCI/MI 0.215% in aqua (aq) detected significantly more patients with MCI/MI allergy than both MCI/MI 0.02% aq (P < 0.001) and MI 0.2% aq (P < 0.001) alone and combined.

CONCLUSIONS

The results favor replacing the preparations MCI/MI 0.02% aq and MI 0.2% aq with the mixture MCI/MI 0.215% aq in the International Contact Dermatitis Research Group baseline series.

Methylchloroisothiazolinone/methylisothiazolinone and methylisothiazolinone contact allergy: A 24-year, single-center, retrospective cohort study from Turkey

BACKGROUND

Methylchloroisothiazolinone/methylisothiazolinone (MCI/MI) and MI allergy caused a global epidemic during the period 2010 to 2015, reaching its peak in 2013/14.

OBJECTIVE

To investigate the characteristics of MCI/MI and MI allergy in Turkey over 24 years.

METHODS

A total of 2310 patients patch tested between 1996 and 2019 with MCI/MI 0.01% aq. or MCI/MI 0.02% aq., with or without MI 0.2% aq., were analyzed.

RESULTS

The overall prevalence of contact sensitization was 3.3% (n = 77) with a peak level of 16.4% in 2015. The prevalence gradually decreased thereafter, but was still high (6.5%) in 2019. Seventy-three patients had clinically relevant sensitizations. MI could detect clinically relevant sensitizations in all seven patients with a negative patch test reaction to MCI/MI 0.02%. Non-occupational allergic contact dermatitis (ACD) was most frequently seen, mainly in women, with hand/face eczema from rinse-off or leave-on cosmetics, such as wet wipes. Occupational ACD was mainly seen among men with airborne eczema from wall paints in house painters, or with hand eczema from hair gel/wax in men's barbers.

CONCLUSIONS

The prevalence of MCI/MI and MI sensitization in Turkey following the peak in 2015 is still high. This is probably due to the currently allowed level of 100 ppm for MI in rinse-off cosmetics. This needs to be urgently reduced.

Methylchloroisothiazolinone and/or Methylisothiazolinone Contact Allergies in Thailand

BACKGROUND

Methylchloroisothiazolinone, in combination with methylisothiazolinone (MCI/MI), and MI alone are common preservatives. The incidences of MCI/MI and MI-alone contact allergies have risen markedly worldwide, leading to changes in their use in products.

OBJECTIVES

The aim of the study was to determine the incidences of positive patch test reactions and factors associated with MCI and/or MI contact allergies during the recent decade in Thailand.

METHODS

Medical records of patients who underwent patch testing at Siriraj Hospital from 2009 to 2018 were retrospectively reviewed. The incidences of positive reactions, histories, and clinical data of MCI/MI and MI-alone contact allergy patients were analyzed.

RESULTS

Of 2789 patients undergoing patch testing, most were female (76.1%). The mean ± SD age was 42.7 ± 15.7 years. Positive reactions to MCI/MI increased from 2009 to 2016 before declining. The MCI/MI contact allergy was most common in females, middle-aged patients, and those with metal allergy histories, with the hands and arms being the predominant sites. However, MI-alone contact allergy was more common in males and mainly at the trunk. Its incidence significantly declined for the last 5 years.

CONCLUSIONS

The incidences of MCI/MI and MI-alone contact allergies began to decline because the Food and Drug Administration Thailand regulations restricted their use. The risk factors for the allergies reported in this study provide important information for patient care.

Amended Safety Assessment of Methylisothiazolinone as Used in Cosmetics

The Cosmetic Ingredient Review Expert Panel (Panel) reviewed the safety of methylisothiazolinone (MI), which functions as a preservative. The Panel reviewed relevant animal and human data provided in this safety assessment and in a previously published safety assessment of MI and concluded that MI is safe for use in rinse-off cosmetic products at concentrations up to 100 ppm and safe in leave-on cosmetic products when they are formulated to be nonsensitizing, which may be determined based on a quantitative risk assessment.

European Surveillance System on Contact Allergies (ESSCA): Contact allergies in relation to body sites in patients with allergic contact dermatitis

Background

Analyses of the European Surveillance System on Contact Allergies (ESSCA) database have focused primarily on the prevalence of contact allergies to the European baseline series, both overall and in subgroups of patients. However, affected body sites have hitherto not been addressed.

Objective

To determine the prevalence of contact allergies for distinct body sites in patients with allergic contact dermatitis (ACD).

Methods

Analysis of data collected by the ESSCA (www.essca‐dc.org) in consecutively patch tested patients, from 2009 to 2014, in eight European countries was performed. Cases were selected on the basis of the presence of minimally one positive patch test reaction to the baseline series, and a final diagnosis of ACD attributed to only one body site.

Results

Six thousand two hundred and fifty‐five cases were analysed. The head and hand were the most common single sites that ACD was attributed to. Differences between countries were seen for several body sites. Nickel, fragrance mix I, cobalt and methylchloroisothiazolinone/methylisothiazolinone were the most frequent allergens reported for various body sites.

Conclusions

Distinct allergen patterns per body site were observed. However, contact allergies were probably not always relevant for the dermatitis that patients presented with. The possibility of linking positive patch test reactions to relevance, along with affected body sites, should be a useful addition to patch test documentation systems.

Isothiazolinone derivatives and allergic contact dermatitis: a review and update

Allergic contact dermatitis (ACD) from isothiazolinones has frequently been described in the literature. Following an epidemic of sensitization to methylchloroisothiazolinone/methylisothiazolinone (MCI/MI) in the 1980s, and more recently to MI, the Scientific Committee on Consumer Safety of the European Commission banned their use in leave-on products, while restricting that in rinse-off cosmetics. Despite a decreasing prevalence of ACD from MCI/MI and MI, cases caused by occupational exposure and non-cosmetic isothiazolinone sources are on the rise. Moreover, sensitization to newer and lesser known isothiazolinones has been reported. This paper reviews the epidemiology of contact allergy to different isothiazolinones, clinical presentation of isothiazolinone-induced ACD, most relevant sensitization sources and potential cross-reactions between isothiazolinone derivatives. It also provides an update on recent legislative measures.

Methylisothiazolinone may induce cell death and inflammatory response through DNA damage in human liver epithelium cells

Methylisothiazolinone (MIT) is a powerful biocide and preservative, which is widely used alone or in a 1:3 ratio with methylchloroisothiazolinone (MCIT) under the trade name of Kathons in the manufacture of numerous personal and household products. Considering that Kathons injected intravenously is distributed in the blood and then in the liver, we explored the toxic mechanism of MIT on human liver epithelium cells. At 24 h after exposure, MIT bound to the plasma membrane and the inner wall of vacuoles in the cells, and rupture of the cell membrane and nuclear envelop, autophagosome-like vacuoles formation and mitochondrial damage were observed. Cell viability dose-dependently decreased accompanying an increase of apoptotic cells, and the level of LDH, NO, IFN-gamma, IL-10 and IL-8, but not IL-1β, significantly increased in the culture media of cells exposed to MIT. Additionally, expression of autophagy-, membrane damage- and apoptosis-related proteins was notably enhanced, and the produced ATP level dose-dependently decreased with the reduced mitochondrial activity. Furthermore, the increased DNA damage and the decreased transcription activity were observed in MIT-treated cells. Meanwhile, the intracellular ROS level did not show dose-dependent change at the same time-point. Then we explored the role of autophagy in MIT-induced cytotoxicity by inhibiting or inducing the autophagic signal. Intriguingly, no additional cell death induced by autophagic modulation occurred when MIT was treated. Taken together, we suggest that MIT may induce multiple pathways of cell death and inflammatory response through DNA damage caused by rupture of the nuclear envelope.

Methylisothiazolinone Contact Allergy Prevalence in Western Canada: Increased Detection With 2000 ppm Patch Test Allergen

Background:

Contact allergy to methylisothiazolinone (MI) or to the combination of methylchloroisothiazolinone and MI (MCI/MI) is an important and increasing cause of allergic contact dermatitis, with prevalence rates higher than 10% in some centers.

Objectives:

The objective of this retrospective chart review is to provide a western Canadian perspective on whether the positive patch testing rate to MCI/MI or MI increased during the testing period of 2008 to 2015 and whether the addition of MI at 2000 ppm resulted in increased detection.

Methods:

We conducted a retrospective chart review of patients who tested positive (n = 104) of 2177 total patients who were patch tested for MCI/MI or MI at a community dermatology clinic in Vancouver, British Columbia, Canada, from January 2008 through April 2015.

Results:

One hundred and four patients had positive patch testing results for MCI/MI, MI, or both. Positive results increased over the study period, with the highest prevalence in 2015 at 9.41% for MCI/MI, 12.94% for MI, and 15.29% for either. When testing for MI at 2000 ppm was introduced in 2013, the initial positive patch testing prevalence was 6.6%, followed by 10.1% in 2014, and 12.9% in 2015.

Conclusions:

We demonstrate an increasing prevalence of MCI/MI and MI allergy between 2008 and 2015, with the highest prevalence of 15.29% in 2015 for MCI/MI and/or MI allergy. The addition of MI 2000 ppm greatly increased the positive patch testing yield for MI. Our results support the importance of continued efforts to monitor and regulate these preservatives.

The Spanish standard patch test series: 2016 update by the Spanish Contact Dermatitis and Skin Allergy Research Group (GEIDAC)

The Spanish standard patch test series, as recommended by the Spanish Contact Dermatitis and Skin Allergy Research Group (GEIDAC), has been updated for 2016. The new series replaces the 2012 version and contains the minimum set of allergens recommended for routine investigation of contact allergy in Spain from 2016 onwards. Four haptens -clioquinol, thimerosal, mercury, and primin- have been eliminated owing to a low frequency of relevant allergic reactions, while 3 new allergens -methylisothiazolinone, diazolidinyl urea, and imidazolidinyl urea- have been added. GEIDAC has also modified the recommended aqueous solution concentrations for the 2 classic, major haptens methylchloroisothiazolinone and methylisothiazolinone, which are now to be tested at 200ppm in aqueous solution, and formaldehyde, which is now to be tested in a 2% aqueous solution. Updating the Spanish standard series is one of the functions of GEIDAC, which is responsible for ensuring that the standard series is suited to the country's epidemiological profile and pattern of contact sensitization.

In situ chemical behaviour of methylisothiazolinone (MI) and methylchloroisothiazolinone (MCI) in reconstructed human epidermis: a new approach to the cross-reactivity issue

BACKGROUND

Methylisothiazolinone (MI) [with methylchloroisothiazolinone (MCI) in a ratio of 1:3, a well-recognized allergenic preservative] was released as an individual preservative in the 2000s for industrial products and in 2005 for cosmetics. The high level of exposure to MI since then has provoked an epidemic of contact allergy to MI, and an increase in MI/MCI allergy. There are questions concerning the MI/MCI cross-reaction pattern.

OBJECTIVES

To bring a new perspective on the MI/MCI cross-reactivity issue by studying their in situ chemical behaviour in 3D reconstructed human epidermis (RHE).

METHODS

MI and MCI were synthesized with (13) C substitution at positions C-4/C-5 and C-5, respectively. Their in situ chemical behaviours in an RHE model were followed by use of the high-resolution magic angle spinning nuclear magnetic resonance technique.

RESULTS

MI was found to react exclusively with cysteine thiol residues, whereas MCI reacted with histidines and lysines. The reaction mechanisms were found to be different for MI and MCI, and the adducts formed had different molecular structures.

CONCLUSION

In RHE, different MI/MCI reactions towards different nucleophilic amino acids were observed, making it difficult to explain cross-reactivity between MI and MCI.

Patch test results in children and adolescents across Europe. Analysis of the ESSCA Network 2002-2010

BACKGROUND

Contact sensitization in children is more frequent than previously thought.

METHODS

The ESSCA collected patch test data from 11 European countries aggregated to 4 European regions.

RESULTS

Six thousand and eight patients aged 1-16 years old with suspected allergic contact dermatitis were analyzed during a period of 8 years (2002-2010). The overall prevalence of at least one positive reaction to a hapten was 36.9%. The 10 most frequent haptens were as follows: nickel sulfate, cobalt chloride and potassium dichromate, neomycin sulfate, Myroxylon pereirae resin (balsam of Peru), para-phenylenediamine, chloromethylisothiazolinone/methylisothiazolinone 3:1, fragrance mix, lanolin alcohols, and colophony. No difference was found in the prevalence of at least one positive reaction to at least one hapten between boys and girls and between children with atopic dermatitis and children without. Children without atopic dermatitis, when compared with those with, had a significantly higher prevalence of contact sensitization for nickel sulfate (20.91% vs 16.87%, respectively), 4-tert. butylphenol formaldehyde resin (1.61% vs. 0.7%), and para-phenylenediamine (2.49% vs. 1.3%).

LIMITATIONS OF THE STUDY

Chamber loading is not an exact science and variation may occur between staff and departments. Interinstitution variations in readings can occur. A possible geographic confounder is that the southern regions tested more children in the younger age group. Relevance was not addressed due to difficulties in the application of a set of uniform definitions.

CONCLUSIONS

Our study adds information on the most common contact allergens detected in children which could help to define a Standard European Pediatric Baseline Series.

Methylisothiazolinone: dermal and respiratory immune responses in mice

Methylisothiazolinone (MI), a widely used chemical preservative in industrial and household products, and cosmetics, has been associated with allergic contact dermatitis. However, the asthmogenic capacity of MI is currently unknown. In this study, we investigated the capacity of MI to elicit asthma-like responses in a validated mouse model. On days 1 and 8, mice (C57Bl/6 and BALB/c) were dermally treated with MI or vehicle on each ear. On day 15, mice received a single intranasal challenge with MI or vehicle. Immediately after the challenge, the early ventilatory response was measured using a double chamber plethysmograph. One day later, airway hyperreactivity, pulmonary inflammation and immune-related parameters were assessed. Dermal treatment with MI in both C57Bl/6 and BALB/c mice induced increased T- and B-cell proliferation in the auricular lymph nodes, along with IFN-γ production and limited increases in total serum IgE, confirming dermal sensitization. An airway challenge with MI led to an early ventilatory response (decreased breathing frequency), indicative for acute sensory irritation. However, 24h later no allergic respiratory response (no airway hyperreactivity (AHR) nor pulmonary inflammation) was found in either mouse strains. Our study indicates that MI can be classified as a strong dermal sensitizer and irritant, but not an asthmogen after initial dermal sensitization, followed by an airway challenge.