Kathon biocide: manifestation of delayed contact dermatitis in guinea pigs is dependent on the concentration for induction and challenge

Persistence of Isothiazolinones in Clothes After Machine Washing

BACKGROUND

Sensitization to methylchloroisothiazolinone (MCI) and methylisothiazolinone (MI) is a worldwide problem. Washing machine detergents are suspected to cause cutaneous symptoms in highly sensitized patients. Little is known about the persistence of isothiazolinones in clothes that have been washed.

OBJECTIVE

The aim of the study was to analyze the possible persistence of MI, MCI, benzisothiazolinone, and octylisothiazolinone in common fabrics after machine washing.

METHODS

Different clothes (cotton, polyester, linen, and wool) were collected, and 4 types of wash were done (control, standard, standard + conditioner, and standard + double rinse). The samples were analyzed using ultrahigh-performance liquid chromatography.

RESULTS

The results showed that the concentrations of isothiazolinones were very low, independent of the type of material or wash. The highest levels were found in the control wash (hand wash), reaching a maximum of 0.4 ppm in the linen.

CONCLUSIONS

Our findings suggest that it is not necessary to recommend that patients sensitized to MI avoid isothiazolinones in machine detergents or fabric conditioners or to double rinse. However, after using the detergent for hand washing (the control in our study), there may remain sufficient concentrations of isothiazolinones in clothes to produce symptoms in highly sensitized patients.

Devising a Tier-based Skin Sensitisation Screening Strategy for Personal Care and Cosmetic Products

Concerns regarding the use of potential skin sensitisers in personal care and cosmetic products continue to grow. The goal of this study was to develop a proof-of-concept tier-based screening strategy for the assessment of skin sensitisation potential by using non-animal methodologies. As a case example, this screening framework was applied to three WEN® by Chaz Dean cleansing conditioners. The first tier of testing utilised the Organisation for Economic Co-operation and Development (OECD) Quantitative Structure Activity Relationship Toolbox profiler to evaluate the skin sensitisation potential of individual ingredients within the formulation; a literature review was performed on the substances that generated in silico alerts. Tier 2 testing utilised the OECD in chemico Test Guideline (TG) 442C to evaluate these substances. Tier 3 testing adapted OECD TG442C to evaluate the formulated product. The literature review on the four substances that generated in silico alerts revealed that they were not sensitising at the concentrations reported in the formulated products. Tier 2 testing demonstrated that these substances were not sensitising at the concentrations tested. Finally, Tier 3 testing revealed that the evaluated cleansing conditioners had low mean percentage peptide depletion at the concentrations tested. Together, the results obtained suggest that the products tested are unlikely to induce skin sensitisation under the given experimental conditions. These findings are in agreement with other in vitro and clinical studies. The proposed tier-based testing approach may be used as a conceptual framework for the prospective safety screening of other personal care and cosmetic products. However, to establish the validity of the proposed testing strategy, further studies must be performed, including comparisons with established models.

6 Final Report on the Safety Assessment of Methylisothiazolinone and Methylchloroisothiazolinone

Methylisothiazolinone and Methylchloroisothiazolinone (MI/MCI) are heterocyclic organic compounds that are used in cosmetics as a broad spectrum preservative system.

MI/MCI was absorbed after oral administration and then was excreted in the urine or feces; storage in the tissues was minimal. Up to 62% of a single percutaneous dose was bound to the site of application 24 hours after exposure. The MI/MCI-CG bound to the skin had a 13.1-day half-life.

MI/MCI was moderately to highly toxic to rats, and highly toxic to rabbits when administered orally, and moderately toxic when applied dermally. MI/MCI was not a cumulative ocular irritant when tested at 55 ppm. The dermal irritation of MI/MCI was concentration dependent but nonirritating to rabbit skin at 560 ppm concentrations; this nonirritating concentration is well above the maximum recommended use concentration.

No treatment-related effects were observed in rats which received MI/MCI in oral doses up to 24.4 mg/kg/day for 2 weeks. Doses of MI/MCI up to 2.8 mg/kg/day applied dermally to rabbits, 5 days per week for 3 weeks, produced moderate irritation at the application site but no systemic toxicity. Dermal application of MI/MCI at doses up to 0.4 mg/kg/day for 3 months produced no systemic toxicity in rabbits. No toxicologically significant treatment-related effects were observed in rats or dogs at doses up to 30 and 28 mg/kg/day, respectively. The result of genotoxic testing of MI/MCI varied with the assay used. Dermal application of 400 ppm MI/MCI-CG, 3 times per week for 30 months, had no local or systemic tumorigenic effect in male mice.

MI/MCI administered by gavage to pregnant rabbits and rats at doses up to 13.3 mg/kg/day was toxic to the dam, embryo, and fetus; the compound was not teratogenic.

MI/MCI is a sensitizer however, the concentration of MI/MCI in cosmetic products which produced sensitization varies. The available human sensitization test data at concentrations of 50 ppm and above are not in agreement. MI/MCI-CG was not a sensitizer or photosensitizer at a concentration of 15 ppm.

It is concluded that Methylisothiazolinone/Methylchloroisothiazolinone may be safely used in “rinse-off” products at a concentration not to exceed 15 ppm and in “leave-on” cosmetic products at a concentration not to exceed 7.5 ppm. The stated safe use concentration refers to a mixture containing 23.3% Methylisothiazolinone and 76.7% Methylchloroisothiazolinone.

Dose-Response Relationships and Threshold Levels in Skin and Respiratory Allergy

A literature study was performed to evaluate dose-response relationships and no-effect levels for sensitization and elicitation in skin- and respiratory allergy. With respect to the skin, dose-response relationships and no-effect levels were found for both intradermal and topical induction, as well as for intradermal and topical elicitation of allergenic responses in epidemiological, clinical, and animal studies. Skin damage or irritation may result in a significant reduction of the no-effect level for a specific compound. With respect to the respiratory tract, dose-response relationships and no-effect levels for induction were found in several human as well as animal studies. Although dose-response relationships for elicitation were found in some epidemiological studies, concentration-response relationships were present only in a limited number of animal studies. Reported results suggest that especially relatively high peak concentrations can induce sensitization, and that prevention of such concentrations will prevent workers from developing respiratory allergy. Moreover, induction of skin sensitization may result in subsequent heightened respiratory responsiveness following inhalation exposure. The threshold concentration for the elicitation of allergic airway reactions in sensitized subjects is generally lower than the threshold to induce sensitization. Therefore, it is important to consider the low threshold levels for elicitation for recommendation of health-based occupational exposure limits, and to avoid high peak concentrations. Notwithstanding the observation of dose-response relationships and no-effect levels, due to a number of uncertainties, no definite conclusions can be drawn about absolute threshold values for allergens with respect to sensitization of and elicitation reactions in the skin and respiratory tract. Most predictive tests are generally meant to detect the potential of a chemical to induce skin and/or respiratory allergy at relatively high doses. Consequently, these tests do not provide information of dose-response relationships at lower doses such as found in, for example, occupational situations. In addition, the observed dose-response relationships and threshold values have been obtained by a wide variety of test methods using different techniques, such as intradermal exposure versus topical or inhalation exposure at the workplace, or using different endpoints, which all appear important for the outcome of the test. Therefore, especially with regard to respiratory allergy, standardized and validated dose-response test methods are urgently required in order to be able to recommend safe exposure levels for allergens at the workplace.

Skin sensitization: strategies for the assessment and management of risk

Allergic contact dermatitis (ACD) is to a considerable extent a preventable disease. Limitation can be achieved by correct identification of skin sensitizers, characterization of their potency, understanding human skin exposure and application of good risk assessment/management strategies. Various methods exist which are accurate for the predictive identification of chemicals that possess skin-sensitizing properties. These are enshrined in regulations that aim to provide a harmonized approach to hazard identification. One of the methods, the local lymph node assay, also delivers information on the relative potency of sensitizers. Efforts are continuing in the European Union and at the Organization for Economic Cooperation and Development to use elements of this information for regulatory categorization of skin sensitizers. However, greater use can be made of this potency information in the application of quantitative risk assessments. Such assessments depend also on the availability of accurate data on human skin exposure, one aspect where legislation has little role to play. Management of risks by restriction of skin exposure is, in contrast, a key point where legislation can play an important role, helping to establish a level playing field for industry and setting good standards based on the legislator's ability to access all data. Ultimately, the combination of accurate hazard identification, potency measurement, risk assessment and management, underpinned by enabling legislation, will lead to reduction of ACD. For individuals who do still develop contact allergy, avoidance of ACD should continue to be a goal, based on raising awareness of skin protection, allergen labelling and other skincare strategies.

Contact allergy epidemics and their controls

Contact dermatitis can be severe and lead to sick leave as well as significant healthcare expenses. The aim of this review is to present the published knowledge on 6 historical epidemics of contact allergy to apply this knowledge on the prevention and control of future contact allergy epidemics. A historical review is performed on nickel, chromium, methyl-chloro-iso-thiazolinone/methyl-iso-thiazolinone, methyl-di-bromo glucaro-nitrile, formaldehyde, and para-phenylenediamine. The first cases of contact dermatitis are mostly occupational, whereas consumer cases appear later. There is often a latency period from the first cases are observed until an epidemic occurs, and the problem is recognized. Finally, no one seems to take responsibility of dealing with the situation, and there are no attempts of regulation until an epidemic is consolidated among consumers for many years. Steps should be taken to prevent contact allergy epidemics. It is essential that dermatologist, scientists, administrators, and consumers organize and structure known methods to accelerate the control of emerging contact allergens.

Guinea pigs in hypersensitivity testing

The aim of the present paper is to mention steps of development of predictive guinea pig animal models for contact sensitization evaluation in parallel with the development of understanding the mechanism of contact sensitization. The guinea pigs methods are reviewed and the presently accepted methods (Buehler test, Maximization test) are discussed in details. Influences on the outcome of guinea pig sensitization assays are mentioned too. The predictability of the guinea pig methods is compared with predictive methods in mice, with human tests (human repeated insult patch test, HRIPT) and epidemiological data. In the last part, a testing strategy and steps for risk assessment of contact sensitizing potential is proposed.

Contact dermatitis from methylisothiazolinone in a paint factory

Introduction of new potential contact-sensitizing chemicals have in the past led to epidemics of contact dermatitis. A new preservative containing only methylisothiazolinone (MI) and not methylchloroisothiazolinone (MCI) has recently been introduced in the European Union for use in products, such as paint, glue and cosmetics. The objective of this article is to describe a factory outbreak of contact allergy to MI and MCI preservatives. This factory outbreak describes allergic contact dermatitis towards MI in 4 patients of 14 persons working at a paint manufacturer. Patch test results from all patients showed positive reactions for MI and MCI/MI. The reactions were stronger for MI than MCI/MI indicating a primary sensitization to MI. The combination of MCI/MI remains widely used, and therefore various patterns of exposure and sensitization could be seen in the future. Our data show that MI holds a potential for eliciting and propably inducing contact allergy in humans. Whether this preservative is safe to use in cosmetics where billions of consumers are exposed needs a care full monitoring.

Quantitative patch and repeated open application testing in methyldibromo glutaronitrile-sensitive patients

Contact allergy to methyldibromo glutaronitrile (MDBGN), often combined with phenoxyethanol (PE) (e.g., Euxyl K 400), increased throughout the 1990s in Europe. Consequently, in 2003, the European Commission banned its use in leave-on products, where its use concentration was considered too high and the non-sensitizing use concentration as yet unknown. The 2 objectives of the study are (a) to find a maximum non-eliciting concentration in a leave-on product in MDBGN/PE-sensitized patients, which could possibly also be considered safe regarding induction and (b) to find the best patch test concentration for MDBGN. We, therefore, performed a use-related test (ROAT) in patients sensitized to MDBGN/PE (n = 39) with 3 concentrations of MDBGN/PE (50, 100 and 250 p.p.m. MDBGN, respectively). A subset of these patients (n = 24) was later patch-tested with various concentrations (0.1, 0.2, 0.3 and 0.5% MDBGN, respectively). 15 patients (38%, 95% confidence interval (CI) = 23-55%) had a negative and 24 (62%; 95% CI = 45-77%) a positive overall repeated open application test (ROAT) result. 13 reacted to the lowest (50 p.p.m.), 8 to the middle (100 p.p.m.) and 3 to the highest concentration (250 p.p.m.) only. In those 13 reacting to the lowest ROAT concentration, dermatitis developed within a few days (1-7). The strength of the initial and the confirmatory patch test result, respectively, and the outcome of the ROAT were positively associated. Of the 24 patients with a use and confirmatory patch test, 15 reacted to 0.1% MDBGN, 16 to 0.2%, 17 to 0.3% and 22 to 0.5%. With the patch test concentration of 0.5%, the number of ROAT-negative patients but patch-test-positive patients increases considerably, particularly due to + reactions. A maximum sensitivity of 94% (95% CI = 70-100%) is reached with a patch test concentration of 0.2%, and is not further improved by increasing the concentration. However, the specificity decreases dramatically from 88 (95% CI = 47-100%) with 0.2% to a mere 12.5% (95% CI = 0-53%) with 0.5%. It can be concluded (a) that for MDBGN 0.2% is very likely the best patch test concentration and (b) that 50 p.p.m. in a leave-on product can elicit contact dermatitis in sensitized persons. We were, therefore, unable to find a safe, still microbicidal, concentration for leave-on products. By contrast, with other contact allergens, dose-response use tests may be able to identify a non-eliciting concentration, which could give valuable clues to a non-inducing (i.e., safe) concentration in products.

Evaluation of the skin sensitizing potency of chemicals by using the existing methods and considerations of relevance for elicitation

The Technical Committee of Classification and Labelling dealing with harmonized classification of substances and classification criteria under Directive 67/548/EEC on behalf of the European Commission nominated an expert group on skin sensitization in order to investigate further the possibility for potency consideration of skin sensitizers for future development of the classification criteria. All substances and preparations should be classified on the basis of their intrinsic properties and should be labelled accordingly with the rules set up in the Directive 67/548/EEC. The classification should be the same under their full life cycle and in the case that there is no harmonized classification the substance or preparation should be self-classified by the manufacturer in accordance with the same criteria. The Directive does not apply to certain preparations in the finished state, such as medical products, cosmetics, food and feeding stuffs, which are subject to specific community legislation. The main questions that are answered in this report are whether it would be possible to give detailed guidance on how to grade allergen potency based on the existing methods, whether such grading could be translated into practical thresholds and whether these could be set for both induction and elicitation. Examples are given for substances falling into various potency groups for skin sensitization relating to results from the local lymph node assay, the guinea pig maximization test, the Buehler method and human experience.

Thresholds of elicitation depend on induction conditions. Could low level exposure induce sub-clinical allergic states that are only elicited under the severe conditions of clinical diagnosis?

While numerous studies have examined dose/response relationships occurring in the experimental induction of contact allergic dermatitis, fewer have examined the effects of varying the doses of both induction and challenge. Recently published studies have however done this and they all show the same remarkable observation: the threshold of elicitation decreases as the doses used to induce the allergy increase. This has important implications. One is that it may be more complicated to determine clear threshold doses below which allergic responses are not seen. It is also proposed that normal exposure to weak allergens such as some fragrance materials may induce "sub-clinical" allergic states which will not be elicited under these same exposure conditions but which may become apparent under the more severe conditions of clinical diagnosis. This may explain why the prevalence of Patch test reactions to some fragrance materials is apparently increasing in the absence of any clearly documented "epidemic" of consumer complaints.

Insights into the quantitative relationship between sensitization and challenge for allergic contact dermatitis reactions

The ability of chemical or pharmaceutical agents to induce allergic contact dermatitis (ACD) is of major health and regulatory concern. As such, tests to identify their sensitizing capacity, such as the guinea pig maximization test and the more recently developed local lymph node assay, are broadly used. Ideally, for risk assessment it is useful to translate results from animal data into establishing safe or no-effect levels for occupational or environmental agents. This, of course, would require consideration of the quantitative relationships between sensitizing and challenge doses as well as other exposure conditions. In the present studies, we modeled two sensitizers, 2,4-dinitrochlorobenzene and squaric acid dibutyl ester, over a large range of concentrations using the LLNA and more traditional tests that measure both sensitization and elicitation responses. Both the sensitization and challenge phases provided similar dose-response curves, demonstrating a threshold followed by a shallow linear increase and eventual plateau at increasing doses. Extending earlier studies by P. S. Friedmann (1994, Immunotoxicology and Immunopharmacology, pp. 589-616, Raven Press, New York) in humans, we observed that the minimum dose required to elicit sensitization or challenge was not static, but rather reflected a "sliding-scale." That is, as the sensitization dose was increased, the concentration required to elicit a challenge response was decreased. Correspondingly, as the challenge dose was increased, the dose required for sensitization was lessened. Taken together, these findings indicate that there is a need to consider dose-response relationships for sensitization and challenge in establishing minimum exposure levels for chemicals that cause ACD.

Labelling of skin sensitizers: the new European Dangerous Preparations Directive

The new Dangerous Preparations Directive (DPD, 1999/45/EC) introduces a special labelling requirement for skin sensitizers in products that are regulated under this Directive. The packaging of products containing 0.1% of a sensitizer must bear the inscription "Contains 'name of sensitizer'. May produce an allergic reaction." The aim is to protect individuals already sensitized by providing information which enables them to avoid products containing ingredients which may elicit their allergy. However, this is only of benefit where such sensitized individuals do exist in the population. Moreover, this labelling requirement does not take into account the potency of the skin sensitizer. For each sensitizer and type of skin exposure, there will be levels below which it will not elicit allergic contact dermatitis reactions in individuals who are sensitized to that chemical. We therefore propose that within the new DPD, it should be possible to override this labelling requirement with well-documented data, to ensure that information provided to the consumer on the product label is not misleading. The current implementation in the DPD of what is in principle a good idea means that further action (legislative changes; scope for derogation) is needed if the potential benefits are not to be lost.

Dose-response studies of contact allergens using 3 guinea pigs models

A multi-dose-response induction protocol for the guinea pig maximization test (GPMT), including a statistical computer program, has earlier been developed to improve the power of predictive tests for identification of contact allergens. This dose-response protocol, with 2 modifications (i.e., increased number of animals in each group and increased number of challenge concentrations) was evaluated in the GPMT, the cumulative contact enhancement test (CCET) and the Freund's complete adjuvant test (FCAT), using potassium dichromate and hydroxycitronellal as model contact allergens. Application of the dose-response protocol on the CCET and the FCAT resulted in either monotone or non-monotone curves with significant dose-response. However, application of the dose-response protocol on the GPMT gave curves with no significant dose-response. The protocol makes it possible to obtain an EC50 value, thus improving the possibility of ranking contact allergens, which is of substantial use for risk assessments. The dose-response protocol could benefit from a few adjustments: a wider span in the induction doses; change to simultaneous increase in intradermal and topical induction doses to obtain a proper dose-response for the GPMT; the addition of further challenge concentrations. In addition the computer program should allow calculation of threshold concentration for sensitization and EC50 value for a non-monotone curve.

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.

Thresholds in contact sensitization: theoretical and practical considerations

The existence of thresholds for both the induction and the elicitation of contact sensitization is an important issue for hazard assessment in this area of toxicology. In this paper, the evidence for such thresholds has been reviewed from both theoretical and practical perspectives. When the mechanisms of skin sensitization are considered, the existence of thresholds can be shown to occur at several stages. They are both quantitative, for example in terms of the degree of protein haptenation and in the sufficiency of the signals for Langerhans cell migration and maturation, as well as qualitative, in terms of the type of immune response that is engaged. Such considerations are evidenced by a substantial body of practical observation. In humans and in animal models of skin sensitization there is abundant evidence for the existence of thresholds for both the induction and the elicitation of reactions. In addition to, and in distinction from, the experimental situation, in the general human population there is extensive evidence for threshold effects. This evidence arises directly from the observation that only a proportion of those who are exposed become sensitized (i.e. are patch test positive), and of that latter group only a proportion develop allergic contact dermatitis.

Skin sensitization thresholds: determination in predictive models

For many years, test methods for the prospective identification of skin sensitizing chemicals have been widely available. However, although these techniques have permitted the identification of the great majority of skin sensitizers, their use in assessing the relative potency of a particular chemical as a human contact allergen has not been well described. A primary reason for this is the inherent difficulty of such an exercise. A complex phenomenon involving interactions between the vehicle, the allergen, the skin and its inflammatory responses takes place during the induction and elicitation of sensitization. All these factors can have a profound effect on the threshold values determined for a skin sensitizer. Consequently, whether the assessment is conducted in humans or in animal models, a threshold concentration is always a function of the method of measurement as much as the potency of the allergen. Although an exhaustive review has not been carried out, this paper considers the attempts that have been made to assess relative potency by the measurement of dose-response relationships and the determination of induction and elicitation thresholds in both animal models and in humans. The latter has special relevance for regulatory toxicology and this matter is given particular attention in this article. Finally, recommendations are made: (a) that threshold concentrations for skin sensitizers should be determined on a case by case basis in relation to the likely mode of skin contact; (b) where the data are used in comparisons of skin sensitization potency, then there should be standardization of the method used for the determinations.

An interlaboratory evaluation of the Buehler test for the identification and classification of skin sensitizers

The correct identification of potential skin sensitizers is an essential first step in enabling a proper risk assessment to be made and to permit the implementation of appropriate risk management practices designed to avoid the induction of sensitization. Consequently, regulatory guidelines around the world demand that new substances are evaluated to assess their skin sensitization potential. There are two guinea pig test methods which are generally recognised, the guinea pig maximisation test (GPMT) and the occluded patch test described by Buehler. In different countries, one procedure seems to be more prevalent and acceptable to regulatory authorities than the other. Notably, in the European Union, the latest revision of the Annex V (Directive 92/32/EC) Test Method for skin sensitization asks that justification should be given in the situation where the notifier does not use the GPMT, which is the preferred method. Thus in this paper, the validity of the Buehler protocol in the context of European legislation is critically examined. Results from two laboratories are collated, showing that the method can identify significant contact allergens, particularly those which would be registered formally as such according to European legislation. It is demonstrated that minor methodological variations can be tolerated without compromising test sensitivity, but it is recommended that suitable positive control testing is the best way to ensure proper test conduct.

Formulation effect on the dermal bioavailability of isothiazolone biocide

A central tenet of the science of toxicology is that the toxic effect of any material monotonically increases with the amount of the material delivered to the target tissue. This is the so-called dose-response relationship. Previous work is discussed in which a dose-response relationship is established for the induction and elicitation of cutaneous contact allergy from the isothiazolone biocide which is a 3 to 1 mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one. The commercial product name for this mixture is Kathon LX biocide. Given a tissue dose-response, this current work determines and demonstrates a difference in risk from aqueous formulations with and without polymer. A lower delivered dose of biocide goes into the skin from an aqueous-based polymeric emulsion or paint than from an aqueous solution or oil-in-water emulsions without polymer. Thus, the estimate of risk, as a direct result of dose, and the determination of a safe use level of a biocide in any particular formulation matrix need to incorporate this reality.

Classification of chemicals as sensitisers based on new test methods

For the last decade, classification schemes worldwide have recognised that certain chemicals may need to be categorised as skin or respiratory sensitisers. Although differing in detail, the schemes use similar criteria for designating materials as sensitisers, based on either direct evidence from exposed humans or the results of predictive guinea pig tests. In the case of respiratory sensitisation, however, there are currently no acceptable animal test methods. With an increasing understanding of cellular immunology in general, and of immune responses in skin and respiratory sensitisation in particular, several laboratories have recently been developing more objective, immunologically-based tests. For skin sensitisation, the two most promising methods are the murine local lymph node assay (LLNA) and the mouse ear swelling test (MEST). Both assays have undergone inter-laboratory validation and it has been shown that they are able to detect reliably moderate to strong sensitisers. The 1992 update of the OECD test guideline for skin sensitisation suggests the use of the LLNA or MEST as a first stage of testing; if a positive result is seen in either assay, a chemical may then be designated (and classified) as a potential sensitiser and it may not be necessary to conduct a guinea pig test. However, if a negative result is obtained, a guinea pig test must be performed. For respiratory sensitisation, although certain guinea pig models of asthma appear to be predictive of the known human response to sensitisers such as diisocyanates and acid anhydrides, the measurement of changes in serum IgE antibodies in mice treated topically with chemicals may represent a simpler and more accurate method of designating chemicals as respiratory sensitisers.

Assessment of the relative skin sensitizing potency of 3 biocides using the murine local lymph node assay

The relative skin-sensitizing potency of 3 biocides, 5-chloro-2-methyl-4-isothiazolin-3-one (the major active ingredient in Kathon CG), 1,2-benzisothiazolin-3-one and 2-methyl-4,5-trimethylene-4-isothiazolin-3-one, was assessed using the murine local lymph node assay. Potency was ranked according to the lowest dose of material which, following epicutaneous exposure, induced a significant proliferation of T lymphocytes in the draining lymph nodes. The results showed that 5-chloro-2-methyl-4-isothiazolin-3-one was able to induce proliferative activity at significantly lower dose levels than the other 2 biocides and that it may therefore be a more potent skin sensitizer.

Contact sensitization to 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one (MCI/MI). A European multicentre study

The frequency of positive reactions to 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one (MCI/MI) were studied at 22 European contact dermatitis clinics over a period of 1 year. A total of 4713 patients participated. All the patients were patch tested with nickel sulphate, formaldehyde, paraben-mix, and MCI/MI. 19.4% of the patients had positive patch tests to nickel, making this the most common allergen. 3% of the patients reacted to 100 ppm MCI/MI, while 2.6% reacted to formaldehyde and 1.1% to parabens. There was great variation in the frequency of MCI/MI sensitivity among the 22 centres. MCI/MI contact allergy was most common among women and in patients with facial dermatitis, while it was rarely seen in patients with dermatitis on the lower legs. There were no fluctuations in the number of positive patch tests to MCI/MI on a monthly basis when the results from all centres were combined. 117 of the 141 MCI/MI sensitized patients included in the study were retested. 88% had positive patch tests when retested. 101 of the MCI/MI-sensitive patients participated in a double-blind, placebo-controlled product use test. This test showed that 31% of the MCI/MI-sensitive patients had a positive reaction to a MCI/MI-preserved product. Only a few patients reacted to a control product. It is concluded that the preservative MCI/MI is an important new contact allergen.

Skin sensitization--a critical review of predictive test methods in animals and man

With the exception of the Draize Test, the guinea-pig test methods currently accepted by regulatory authorities worldwide are well able to predict the potential of a material to cause skin sensitization. Nevertheless, (a) some methods are more sensitive than others (e.g. adjuvant tests are generally more sensitive than non-adjuvant tests); (b) methods cannot be sufficiently standardized to give full reproducibility of results between laboratories; and (c) most methods are based on subjective visual grading of skin reactions--difficulties thus arise when testing coloured or irritant materials. Laboratories must be able to show the sensitivity of the method(s) they use by demonstrating that positive reactions occur with mild/moderate contact allergens rather than the strong/extreme sensitizers currently recommended in certain guidelines, specifically in the EEC Test Method. The sensitivity of the adjuvant tests is such that it is possible to halve the minimum number of animals required by present regulatory guidelines without compromising the capacity of the tests to detect weak/mild sensitizers. A similar review has not yet been made for non-adjuvant tests. Alternative test methods, including some recently developed mouse models, offer several advantages, including more objective endpoints. These tests have not been extensively validated and this precludes their use at present for regulatory purposes other than to confirm the sensitization potential of a material. Two new test methods using mice, the Mouse Ear-swelling Test and the Local Lymph Node Assay, appear promising. They should undergo rigorous interlaboratory testing to determine their sensitivity and specificity. In vitro methods do not represent a viable alternative in the foreseeable future. An approach using quantitative structure-activity relationships is the most likely route to a non-animal model, but this will require considerable research, development and validation. Human sensitization tests have generally not been used for the classification of substances as non-sensitizers. This is because of an absence of internationally agreed test protocols, the lack of positive controls and because the methods for establishing the sensitivity of human tests are less developed than for animal tests. Nevertheless, for products for which direct human contact is intended, predictive tests in human volunteers can be considered. The EEC Directive for the Classification, Packaging and Labelling of Dangerous Substances provides a reasonable approach to the evaluation of skin sensitizers.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

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.

Sensitivity to Kathon CG: findings in 365 consecutive patients

In the period from 1983 through 1986, 365 consecutive patients suspected as having allergic contact dermatitis were tested for reaction to Kathon CG. This test was positive in 20 of these patients: irritant responses in 7 and allergic sensitivity in 13. Provocative use testing was positive in 1 of the 3 allergic patients tested. The characteristics of this group of patients include having a mean age older than that of the general population or of our population of dermatologic patients, having histories of long-standing dermatitis, and reporting exposure to various leave-on formulations. Our rate of positive tests, 3.6%, is similar to that reported by other investigators, although sensitivity testing results differ from center to center. It is recommended that, in certain clinical situations, caution be exercised in the unsupervised use of leave-on products containing Kathon CG.

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

In 1396 consecutively patch tested patients 18 (1.3%) reacted to Kathon CG. Relevance was established in 4 of the 18 patients. The frequency of positive reactions to Kathon CG in eczema patients seems to have been stable in Denmark during the period 1983 to 1988.

Kathon CG: a review

Kathon CG, a cosmetics preservative containing, as active ingredients, 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one, appears to be a frequent cause of contact dermatitis in Europe. In the United States, where Kathon CG was introduced some 5 years later, the use of this preservative system for cosmetics and toiletries is rapidly increasing. Undoubtedly cases of contact sensitization will soon emerge in this country. Most cases of contact allergy are caused by the use of moisturizing creams on (slightly) damaged skin. Sensitization by the use of cosmetic products on previously healthy skin, especially the face, does occur but appears to be less frequent. Rinse-off products do not seem to have a substantial potential for the induction and elicitation of contact allergic reactions to Kathon CG because of dilution of the product and the allergen with water as well as a short contact time with the skin. This review provides a synopsis of current knowledge on the preservative system Kathon CG, with emphasis on the risk of sensitization and diagnostic procedures.

Human safety study of body lotion containing Kathon CG

The safety of Kathon CG biocide as a preservative in leave-on body lotions was assessed by 2 double-blind studies, using similar protocols. A total of 209 healthy male and female subjects aged 18 to 65 years, 100 in California (72 test subjects, 28 controls) and 109 in Florida (88 test subjects, 21 controls) completed the studies which included pre- and post-use phase diagnostic patch testing with Kathon CG 100 ppm active ingredient, and 13 weeks daily applications of either a test lotion containing Kathon CG 15 ppm active ingredient or a control lotion without Kathon CG. No evidence of irritation or sensitization attributable to use of the biocide was found during regular dermatological examinations during the use phase. Post-use phase patch testing produced negative results in all subjects with the exception of 1 control subject in Florida who had positive readings at the 2- and 4-week post-use phase patch testing. Overall, these studies show there is minimal, if any, risk of adverse effects associated with the use of Kathon CG 15 ppm active ingredient in a leave-on application.

Rapid increase in contact allergy to Kathon CG in Finland

In unselected eczema patients subjected to routine patch testing, the number with positive reactions to Kathon CG 100 ppm increased from none in 1983 to 0.7% in January-August 1985, and to 4.6% in September 1985 to March 1986. Repeated open application tests (ROAT) with creams containing 7-15 ppm of the isothiazolinones were positive in 12 of 24 patients tested. 2 of the ROAT-positive cases had negative patch tests to 100 ppm Kathon CG, but 1 was positive with 200 ppm. Atopic dermatitis, chronic hand dermatitis and lower leg dermatitis were the most common disorders in the positive patients. The cause of the rapid increase of Kathon CG allergy in Finland during the winter of 1985-1986 was the use of a popular moisturizing cream containing first 19 ppm, then 7 ppm of a mixture of 2 isothiazolinones (Euxyl K 100).

Dose-response assessments of Kathon biocide. (II). Threshold prophetic patch testing

Biocidal preservative agents are important in preventing the growth of pathogenic and nonpathogenic organisms in a variety of personal care, household and industrial products. Nearly all effective, commonly used preservative materials possess skin sensitization potential. In a series of 13 prophetic human repeat insult patch tests involving a total of 1450 subjects, no skin sensitization was induced at concentrations of 10 ppm, 6 ppm or 5 ppm (1121 subjects) or at 15 ppm (200 subjects) of a new isothiazolinone preservative mixture (Kathon CG). Delayed contact hypersensitivity was induced in 1 of 84 subjects at 12.5 ppm and in 2 of 45 subjects at 20 ppm. These results add further support to the previously reported conclusion that use of this new biocide at the very low concentrations required for effective preservation of rinse-off products involves an extremely low risk of clinical dermatoses.