Skin sensitization quantitative risk assessment: A review of underlying assumptions

Risk assessment-based verification of the CertiPURTM limit values for toluene diamine and methylene dianiline in flexible polyurethane foam

Flexible polyurethane foams (PUF) are used in many consumer products. PUF may contain trace levels of aromatic diamine impurities that could represent a potential health risk. The risk associated with sleeping on a PUF mattress was evaluated. Toxicity benchmarks for sensitization and non-cancer endpoints were derived from the respective points-of-departure using standard assessment factors. For the cancer endpoints, toxicity benchmarks were derived from the 25th-percentile values of animal studies. Recently published emission and migration data allowed to link exposure with the CertiPURTM voluntary quality limits of ≤5 mg.kg-1 for 2,4-toluene diamine and 4,4'-methylene dianiline in PUF. Using conservative exposure scenarios, lifetime-average daily internal doses from the combined inhalation and dermal exposures were calculated. Margins of safety for non-cancer and sensitization endpoints were >104. The theoretical excess cancer risk was ≤1.5 × 10-7. It is concluded that sleeping on a mattress that satisfies the CertiPUR limit value does not pose undue risk to consumers.

PACEMweb: a tool for aggregate consumer exposure assessment

BACKGROUND

To ascertain the safe use of chemicals that are used in multiple consumer products, the aggregate human exposure, arising from combined use of multiple consumer products needs to be assessed.

OBJECTIVE

In this work the Probabilistic Aggregate Consumer Exposure Model (PACEM) is presented and discussed. PACEM is implemented in the publicly available web tool, PACEMweb, for aggregate consumer exposure assessment.

METHODS

PACEM uses a person-oriented simulation method that is based on realistic product usage information obtained in surveys from several European countries. PACEM evaluates aggregate exposure in a population considering individual use and co-use patterns as well as variation in product composition. Product usage data is included on personal care products (PCPs) and household cleaning products (HCPs).

RESULTS

PACEM has been implemented in a web tool that supports broad use in research as well as regulatory risk assessment. PACEM has been evaluated in a number of applications, testing and illustrating the advantage of the person-oriented modeling method. Also, PACEM assessments have been evaluated by comparing its results with biomonitoring information.

SIGNIFICANCE

PACEM enables the assessment of realistic aggregate exposure to chemicals in consumer products. It provides detailed insight into the distribution of exposure in a population as well as products that contribute the most to exposure. This allows for better informed decision making in the risk management of chemicals.

IMPACT

Realistic assessment of the total, aggregate exposure of consumers to chemicals in consumer products is necessary to guarantee the safe use of chemicals in these products. PACEMweb provides, for the first time, a publicly available tool to assist in realistic aggregate exposure assessment of consumers to chemicals in consumer products.

Quantitative risk assessment of skin sensitising pesticides: Clinical and toxicological considerations

Like many other consumer and occupational products, pesticide formulations may contain active ingredients or co-formulants which have the potential to cause skin sensitisation. Currently, there is little evidence they do, but that could just reflect lack of clinical investigation. Consequently, it is necessary to carry out a safety evaluation process, quantifying risks so that they can be properly managed. A workshop on this topic in 2022 discussed how best to undertake quantitative risk assessment (QRA) for pesticide products, including learning from the experience of industries, notably cosmetics, that already undertake such a process routinely. It also addressed ways to remedy the matter of clinical investigation, even if only to demonstrate the absence of a problem. Workshop participants concluded that QRA for skin sensitisers in pesticide formulations was possible, but required careful justification of any safety factors applied, as well as improvements to the estimation of skin exposure. The need for regulations to stay abreast of the science was also noted. Ultimately, the success of any risk assessment/management for skin sensitisers must be judged by the clinical picture. Accordingly, the workshop participants encouraged the development of more active skin health monitoring amongst groups most exposed to the products.

Assessing the risk of induction of skin sensitization to plant protection products: A quantitative approach

Exposure to skin sensitizers is common and regulated in many industry sectors. For cosmetics, a risk-based approach has been implemented, focused on preventing the induction of sensitization. First, a No Expected Sensitization Induction Level (NESIL) is derived, then modified by Sensitization Assessment Factors (SAFs) to derive an Acceptable Exposure Level (AEL). The AEL is used in risk assessment, being compared with an estimated exposure dose, specific to the exposure scenario. Since in Europe there is increased concern regarding exposure towards potentially sensitizing pesticides via spray drift, we explore how existing practice can be modified to allow Quantitative Risk Assessment (QRA) of pesticides for bystanders and residents. NESIL derivation by the Local Lymph Node Assay (LLNA), the globally required in vivo assay for this endpoint, is reviewed alongside consideration of appropriate SAFs. Using a case study, the principle that the NESIL in μg/cm² can be derived by multiplying LLNA EC3% figure by a factor of 250 is adopted. The NESIL is then reduced by an overall SAF of 25 to establish an exposure level below which there is minimal bystander and resident risk. Whilst this paper focuses on European risk assessment and management, the approach is generic and universally applicable.

Risk management of skin sensitisers: A commentary

Historically, allergic contact dermatitis (ACD) to chemicals encouraged hazard identification improvements, more sophisticated risk assessment and implementation of regulatory strategies, including banning of specific sensitising substances. The validation process applied to hazard identification methods demonstrates their accuracy; their use to characterise sensitiser potency facilitates quantitative and transparent risk assessment. Diagnostic patch testing at dermatology clinics worldwide delivers feedback showing where risk assessment/management has been insufficient or did not target the exposure of concern, thereby facilitating improvements. When urgent action to protect human health was required, regulations limited/banned, specific skin sensitisers. This can be seen in practice with the fragrance industry, a known source of ACD, thus requiring risk management, usually restrictions to limit allergy induction, and very rarely specific bans on ingredients. Experience and development of more sophisticated tools, e.g. to assess aggregate exposure from multitude of consumer product types, has led to repeated adaptation of risk assessment and promulgation of updated fragrance use limits. Although targeted control may not always lead to rapid change in the overall clinical picture, it is preferable to a blanket undifferentiated regulatory control of all sensitisers, resulting in unwarranted restrictions for many uses of no health concern, with consequent substantial socio-economic impacts.

Retrospective quantitative risk assessment of skin sensitization caused by an antimicrobial agent used in a consumer product: 2,3,5,6-Tetrachloro-4-(methylsulfonyl) pyridine

BACKGROUND

Serious cases of allergic contact dermatitis (ACD) caused by exposure to 3,5,6-tetrachloro-4-(methylsulfonyl)pyridine (TCMSP; CAS no. 13108-52-6) used as an antimicrobial agent for desk mats have been reported in Japan.

OBJECTIVE

A quantitative risk assessment (QRA) of TCMSP contained in desk mats was performed retrospectively.

MATERIALS AND METHODS

A local lymph node assay (LLNA): BrdU-ELISA was conducted to determine a reliable EC1.6 value for TCMSP. The acceptable exposure level (AEL) for TCMSP was derived from the EC1.6 value by applying sensitization assessment factors (SAFs). The exposure level was estimated based on the assumption referring to the use conditions of thiabendazole in the same purpose. Then, the estimated exposure level was compared with the AEL to evaluate the skin sensitization risk.

RESULTS

The AEL was calculated as 0.00458 μg/cm² based on the EC1.6 value (0.011%, 2.75 μg/cm² ) by applying a composite SAF of 600. The estimated TCMSP exposure level from the desk mat was 500 times greater than the AEL, indicating a serious skin sensitization risk.

CONCLUSIONS

Assessments of skin sensitization potencies of chemicals to be used in consumer products are strongly recommended, and QRAs should be performed at the pre-marketing stage to avoid the skin sensitization risk in consumers.

Semiquantitative sensitization safety assessment of extractable and leachables associated with parenteral pharmaceutical products

Extractable and leachables (E&Ls) associated with parenteral pharmaceutical products should be assessed for patient safety. One essential safety endpoint is local or systemic sensitization. However, there are no regulatory guidelines for quantitative sensitization safety assessment of E&Ls. A semiquantitative sensitization safety assessment workflow is developed to refine the sensitization safety assessment of E&Ls associated with parenteral pharmaceutical products. The workflow is composed of two sequential steps: local skin sensitization and systemic sensitization safety assessment. The local skin sensitization step has four tiers. The output from this step is the acceptable exposure level for local sensitization (AEL_ls) and this safety threshold can be used for local sensitization safety assessment. From the derived AEL_ls, the systemic sensitization safety assessment at step 2 proceeds in 2 tiers. The output from this workflow is the derivation of acceptable exposure level for systemic sensitization (AEL_ss). When the estimated human daily exposure (HDE) is compared with the AEL_ss, the margin of exposure is calculated to determine the sensitization safety of E&Ls following parenteral administration. The current work represents an initial effort to develop a scientifically robust process for sensitization safety assessment of E&Ls associated with parenteral pharmaceutical products.

Comparison of the acceptable surface limits derived from the skin sensitization potency for workers and swab residue limits determined from the permitted daily exposure derived from the systemic effects

Allergic contact dermatitis is a common occupational and environmental health problem and setting of health-based exposure limits (HBELs) to prevent induction of skin sensitization is strongly desired. When manufacturing pharmaceuticals in a shared facility, cleaning validation using surface residue levels (SRLs) derived from permitted daily exposures (PDEs) is conducted to avoid cross-contamination from the perspective of protecting patients; however, it is unclear whether the SRLs are sufficient to prevent induction of skin sensitization for workers as well. In this study, we compared acceptable surface limits (ASLs) derived from acceptable exposure levels (AELs) based on EC1.6 obtained from local lymph node assay (LLNA): BrdU-ELISA for occupational risk management of skin sensitizers with PDE-based SRLs. ASLs for 1,4-phenylenediamine (GHS skin sensitization sub-category 1A), isoeugenol (sub-category 1A), and methyl methacrylate (sub-category 1B) were compared with SRLs based on the PDEs derived from their systemic effects. The results yielded an SRL for 1,4-phenylenediamine (PDE: 0.8 mg/day) of 30 mg/100 cm2, almost 1,000 times higher than ASL (0.031 mg/100 cm2) derived from its skin sensitization potency. SRL for isoeugenol (PDE: 3.1 mg/day) was 130 mg/100 cm2, over 500 times higher than ASL (0.18 mg/100 cm2). For methyl methacrylate (PDE: 5 mg/day) as well, SRL (200 mg/100 cm2) was higher, but it was within 20 times the ASL (10 mg/100 cm2). These results showed that ASL-based risk management is extremely important especially for strong sensitizers classified as GHS sub-category 1A for occupational skin sensitization risk management.

Quantitative risk assessment of allergens leaching from menstrual hygiene products

Allergic contact dermatitis (ACD) often associated with the topical use of perfumed products, remains one of the most common chronic skin disorders in Western countries. Since labelling of scented menstrual hygiene products (MHPs) is not mandatory, women might be unknowingly exposed to allergens. Given that vaginal mucosae lack the vital barrier function of the skin, skin allergens can easily penetrate and become systemically available and hence women may experience adverse effects in the anogenital region. The aim of this study was therefore to investigate whether women using scented MHPs are at risk of sensitization and hence developing ACD. Hereto, a Quantitative Risk Assessment (QRA) is performed on four well-known skin sensitizing chemicals (α-isomethyl ionone, benzyl salicylate, hexyl cinnamaldehyde and heliotropine) that were previously found leaching from five different scented MHPs including tampons and sanitary pads. The amounts of heliotropine, leached by one of the investigated tampons, exceeded acceptable exposure levels determined with the QRA and could induce sensitization. In addition, although no sensitization is expected for the other three compounds, an allergenic reaction might be provoked in women who are already sensitized. Labelling of allergens on scented MHPs would therefore help consumers to prevent adverse effects linked to ACD.

Decision making in next generation risk assessment for skin allergy: Using historical clinical experience to benchmark risk

Our aim is to develop and apply next generation approaches to skin allergy risk assessment that do not require new animal test data and better quantify uncertainties. Quantitative risk assessment for skin sensitisation uses safety assessment factors to extrapolate from the point-of-departure to an acceptable human exposure level. It is currently unclear whether these safety assessment factors are appropriate when using non-animal test data to derive a point-of departure. Our skin allergy risk assessment model Defined Approach uses Bayesian statistics to infer a human-relevant metric of sensitiser potency with explicit quantification of uncertainty, using any combination of human repeat insult patch test, local lymph node assay, direct peptide reactivity assay, KeratinoSens™, h-CLAT or U-SENS™ data. Here we describe the incorporation of benchmark exposures pertaining to use of consumer products with clinical data supporting a high/low risk categorisation for skin sensitisation. Margins-of-exposure (potency estimate to consumer exposure level ratio) are regressed against the benchmark risk classifications, enabling derivation of a risk metric defined as the probability that an exposure is low risk. This approach circumvents the use of safety assessment factors and provides a simple and transparent mechanism whereby clinical experience can directly feed-back into risk assessment decisions.

The 2-Methoxymethyl Modification of p-Phenylenediamine Reduces the Sensitization Risk for Hairdressers to Hair Dyes-An Occupational Hand Exposure-Based Risk Assessment

BACKGROUND

Allergic contact dermatitis involving the hands is a common occupational skin disease for hairdressers and the potent sensitizers p-phenylenediamine (PPD) and toluene-2,5-diamine (PTD) are associated with the development of occupational allergic contact dermatitis.

OBJECTIVE

The aim of the study was to analyze whether the use of the moderate sensitizer 2-methoxymethyl-PPD (ME-PPD) in professional hair dyes is a suitable tool to reduce the occupational contact allergy risk for hairdressers.

METHODS

Hand exposure of hairdressers (N = 11) to ME-PPD was analyzed under routine hair coloring conditions in commercial salons. By accounting for wet work and uneven hand exposure, the daily hand exposure was derived and compared with the occupational acceptable exposure level (AEL), that is, the sensitization induction threshold of ME-PPD adjusted for interindividual variability among workers.

RESULTS

The daily hand exposure to ME-PPD was 1.6 μg/cm2, and the occupational AEL was 215 μg/cm2. The ratio of hand exposure to AEL was calculated as the margin of safety (MOS) against occupational sensitization. For ME-PPD, the MOS of 134 indicates a low likelihood of sensitization versus PPD and PTD with MOS values of 2.7 and 5.9, respectively.

CONCLUSIONS

Our data predict that the use of ME-PPD in professional hair color products improves the protection of hairdressers against hair dye-related contact allergy versus the use of PPD and PTD.

Framework for sensitization assessment of extractables and leachables in pharmaceuticals

During the toxicological assessment of extractables and leachables in drug products, localized hazards such as irritation or sensitization may be identified. Typically, because of the low concentration at which leachables occur in pharmaceuticals, irritation is of minimal concern; therefore, this manuscript focuses on sensitization potential. The primary objective of performing a leachable sensitization assessment is protection against Type IV induction of sensitization, rather than prevention of an elicitation response, as it is not possible to account for the immunological state of every individual. Sensitizers have a wide range of potencies and those which induce sensitization upon exposure at a low concentration (i.e. strong, or extreme sensitizers) pose the highest risk to patients and should be the focus of the risk assessment. The Extractables and Leachables Safety Information Exchange (ELSIE) consortium has reviewed the status of dermal, respiratory, and systemic risk assessment in cosmetic and pharmaceutical industries, and proposes a framework to evaluate the safety of known or potential dermal sensitizers in pharmaceuticals. Due to the lack of specific regulatory guidance on this topic, the science-driven risk-based approach proposed by ELSIE encourages consistency in the toxicological assessment of extractables and leachables to maintain high product quality and ensure patient safety.

Acceptable Surface Limits (ASLs) of skin sensitizers derived from the local lymph node assay (LLNA): BrdU-ELISA EC1.6 values and their relationships to known sensitization potency information

Skin sensitization is an extremely important risk factor for occupational health and safety and it would be desirable to set Health-Based Exposure Limits (HBELs) for the Quantitative Risk Assessment (QRA) based on the skin sensitizing potencies of chemical. We attempted to set Acceptable Surface Limits (ASLs) as HBELs for skin sensitizers in the workplace based on the local lymph node assay (LLNA): BrdU-ELISA EC1.6 values. To calculate the ASLs, a Safety Assessment Factor (SAF)_interspecies value of 6, based on the EC1.6 values/Human Repeat Insult Patch Test (HRIPT) NOEL ratios, a SAF_{inter-individual} value of 10, and a SAF_{frequency/duration} value of 3 were applied, referring to previous literatures on SAFs for skin sensitization QRA, and the composite SAF was calculated as 180. The ASLs (mg/100 cm² ) derived thus for 33 chemicals ranged from 0.001 to 10.417. Comparison of the ranges with known human sensitization potency classes and GHS subcategories revealed that use of GHS Category 1A chemicals needs to be controlled to ensure surface residue levels of less than 1 mg/100 cm² . To minimize sensitization risks, a quantitative sensitization risk assessment method for chemicals and appropriate risk management are necessary. This report provides a potentially useful ASL-based method of managing sensitization risk derived from LLNA: BrdU-ELISA EC1.6 values, comparison of the ASLs and known human sensitization potency data showed that GHS subcategorization results would be a primary information notifying ASL ranges to be required for minimizing the sensitization risk.

Implementation of a dermal sensitization threshold (DST) concept for risk assessment: structure-based DST and in vitro data-based DST

Skin sensitization resulting in allergic contact dermatitis represents an important toxicological endpoint as part of safety assessments. When available substance-specific sensitization data are inadequate, the dermal sensitization threshold (DST) concept has been proposed to set a skin exposure threshold to provide no appreciable risk of skin sensitization. Structure-based DSTs, which include non-reactive, reactive, and high potency category (HPC) DSTs, can be applied to substances with an identified chemical structures. An in vitro data-based "mixture DST" can be applied to mixtures based on data from in vitro test methods, such as KeratinoSens™ and the human Cell Line Activation Test. The purpose of this review article is to discuss the practical use of DSTs for conducting sound sensitization risk assessments to assure the safety of consumer products. To this end, several improvements are discussed in this review. For application of structure-based DSTs, an overall structural classification workflow was developed to exclude the possibility that "HPC but non-reactive" chemicals are misclassified as "non-reactive", because such chemicals should be classified as HPC chemicals considering that HPC rules have been based on the chemical structure of high potency sensitizers. Besides that, an extended application of the mixture DST principle to mixtures that either is cytotoxic or evaluated as positive was proposed. On a final note, we also developed workflows that integrate structure-based and in vitro-based mixture DST. The proposed workflows enable the application of the appropriate DST, which serves as a point of departure in the quantitative sensitization risk assessment.

Skin Sensitization Testing: The Ascendancy of Non-Animal Methods

A century ago, toxicology was an empirical science identifying substance hazards in surrogate mammalian models. Over several decades, these models improved, evolved to reduce animal usage, and recently have begun the process of dispensing with animals entirely. However, despite good hazard identification, the translation of hazards into adequately assessed risks to human health often has presented challenges. Unfortunately, many skin sensitizers known to produce contact allergy in humans, despite being readily identified as such in the predictive assays, continue to cause this adverse health effect. Increasing the rigour of hazard identification is inappropriate. Regulatory action has only proven effective via complete bans of individual substances. Since the problem applies to a broad range of substances and industry categories, and since generic banning of skin sensitizers would be an economic catastrophe, the solution is surprisingly simple—they should be subject to rigorous safety assessment, with the risks thereby managed accordingly. The ascendancy of non-animal methods in skin sensitization is giving unparalleled opportunities in which toxicologists, risk assessors, and regulators can work in concert to achieve a better outcome for the protection of human health than has been delivered by the in vivo methods and associated regulations that they are replacing.

A critical review of the kinetic direct peptide reactivity assay (kDPRA) for skin sensitizer potency assessment - taking it forward

It is widely recognized that the ability of chemicals to sensitize, and the potency of those chemicals that are sensitizers, is related to their ability to covalently modify protein in the skin. With the object of putting non-animal-based prediction of skin sensitization on a more quantitative footing, a recent paper describes the development of the kinetic Direct Protein Reactivity Assay (kDPRA), in which a matrix of peptide depletion values for different reaction times and test chemical concentrations is generated and analyzed so as to derive a reactivity parameter, logk_max, which is used to classify chemicals into one of two potency categories. The present paper demonstrates that the reaction chemistry is not always consistent with the mathematical analysis of the data matrix and the kDPRA protocol does not identify such cases. Consequently the derived logk_max value is not always mechanistically meaningful and its application to predict potency can lead to misleading conclusions. It is shown that by adopting a data analysis protocol based on conventional kinetics practice, the kDPRA can be made to provide more reliably meaningful and more extensive information that can be used for purposes such as potency estimation for deriving No Expected Sensitization Induction Level (NESILs) required for quantitative risk assessment (QRA), deriving quality specifications in terms of acceptable impurity levels, and development of structure-activity relationships. Secondly, the paper addresses applicability domain issues, in particular the problem of deciding whether or not the kDPRA is applicable for a given chemical.

Safety Testing of Cosmetic Products: Overview of Established Methods and New Approach Methodologies (NAMs)

Cosmetic products need to have a proven efficacy combined with a comprehensive toxicological assessment. Before the current Cosmetic regulation N°1223/2009, the 7th Amendment to the European Cosmetics Directive has banned animal testing for cosmetic products and for cosmetic ingredients in 2004 and 2009, respectively. An increasing number of alternatives to animal testing has been developed and validated for safety and efficacy testing of cosmetic products and cosmetic ingredients. For example, 2D cell culture models derived from human skin can be used to evaluate anti-inflammatory properties, or to predict skin sensitization potential; 3D human skin equivalent models are used to evaluate skin irritation potential; and excised human skin is used as the gold standard for the evaluation of dermal absorption. The aim of this manuscript is to give an overview of the main in vitro and ex vivo alternative models used in the safety testing of cosmetic products with a focus on regulatory requirements, genotoxicity potential, skin sensitization potential, skin and eye irritation, endocrine properties, and dermal absorption. Advantages and limitations of each model in safety testing of cosmetic products are discussed and novel technologies capable of addressing these limitations are presented.

The clonal structure and dynamics of the human T cell response to an organic chemical hapten

Diphenylcyclopropenone (DPC) is an organic chemical hapten which induces allergic contact dermatitis and is used in the treatment of warts, melanoma, and alopecia areata. This therapeutic setting therefore provided an opportunity to study T cell receptor (TCR) repertoire changes in response to hapten sensitization in humans. Repeated exposure to DPC induced highly dynamic transient expansions of a polyclonal diverse T cell population. The number of TCRs expanded early after sensitization varies between individuals and predicts the magnitude of the allergic reaction. The expanded TCRs show preferential TCR V and J gene usage and consist of clusters of TCRs with similar sequences, two characteristic features of antigen-driven responses. The expanded TCRs share subtle sequence motifs that can be captured using a dynamic Bayesian network. These observations suggest the response to DPC is mediated by a polyclonal population of T cells recognizing a small number of dominant antigens.

Skin Sensitization Tests: The LLNA and the RhE IL-18 Potency Assay

Contact allergy is of considerable importance to the toxicologist, and regulatory authorities worldwide require testing for skin sensitization potential and appropriate hazard labeling to enable management of the risk to human health. Although traditionally the identification of skin-sensitizing chemicals has been carried out using animal models, in Europe legislative changes have promoted, and now require, the use of non-animal methods (i.e., Cosmetic Directive, REACH). Several in vitro alternatives for hazard identification have now been validated, but do not provide information on the potency of a skin sensitizer. Here, we describe an animal model, the local lymph node assay (LLNA), and an in vitro model, the RhE IL-18 potency assay, in the context of the identification and potency classification of skin sensitizers. These two assays have been chosen among the different available tests as representative of an alternative in vivo model (the LLNA) and a promising in vitro method with the potential of both hazard identification and potency classification.

The activity of methacrylate esters in skin sensitisation test methods II. A review of complementary and additional analyses

Allergic contact dermatitis is an important occupational health issue, and there is a need to identify accurately those chemicals that have the potential to induce skin sensitisation. Hazard identification was performed initially using animal (guinea pig and mouse) models. More recently, as a result of the drive towards non-animal methods, alternative in vitro and in silico approaches have been developed. Some of these new in vitro methods have been formally validated and have been assigned OECD Test Guideline status. The performance of some of these recently developed in vitro methods, and of 2 quantitative structure-activity relationships (QSAR) approaches, with a series of methacrylate esters has been reviewed and reported previously. In this article that first review has been extended further with additional data and complementary analyses. Results obtained using in vitro methods (Direct Peptide Reactivity Assay, DPRA; ARE-Nrf2 luciferase test methods, KeratinoSens and LuSens; Epidermal Sensitisation Assay, EpiSensA; human Cell Line Activation Test, h-CLAT, and the myeloid U937 Skin Sensitisation test, U-SENS), and 2 QSAR approaches (DEREK™-nexus and TIMES-SS), with 11 methacrylate esters and methacrylic acid are reported here, and compared with existing data from the guinea pig maximisation test and the local lymph node assay. With this series of chemicals it was found that some in vitro tests (DPRA and ARE-Nrf2 luciferase) performed well in comparison with animal test results and available human skin sensitisation data. Other in vitro tests (EpiSensA and h-CLAT) proved rather more problematic. Results with DEREK™-nexus and TIMES-SS failed to reflect accurately the skin sensitisation potential of the methacrylate esters. The implications for assessment of skin sensitising activity are discussed.

Total dose defines the incidence of percutaneous IgE/IgG1 mediated immediate-type hypersensitivity caused by papain

Assessment of human health risk requires an understanding of antigen dose metrics associated with toxicity. Whereas assessment of the human health risk for delayed-type hypersensitivity is understood, the metrics remain unclear for percutaneous immediate-type hypersensitivity (ITH) mediated by IgE/IgG1. In this work, we aimed to investigate the dose metric for percutaneous ITH mediated by IgE/IgG1 responses. Papain, which causes ITH via percutaneous sensitization in humans, was used to sensitize guinea pigs and mice. The total dose per animal or dose per unit area was adjusted to understand the drivers of sensitization. Passive cutaneous anaphylaxis (PCA) and enzyme-linked immunosorbent assay (ELISA) for papain-specific IgG1 enabled quantification of the response in guinea pigs. In mice, the number of antigen-bearing B cells in the draining lymph nodes (DLN) was calculated using flow cytometry papain-specific IgG1 and IgE levels were quantified by ELISA. PCA positive test rates and the amounts of antigen-specific antibody corresponded with total dose per animal, not dose per unit area. Furthermore, the number of B cells taking up antigen within DLN also correlated with total dose. These findings indicate that the total antigen dose is the important metric for percutaneous IgE/IgG1-mediated ITH.

Updating exposure assessment for skin sensitization quantitative risk assessment for fragrance materials

In 2008, a proposal for assessing the risk of induction of skin sensitization to fragrance materials Quantitative Risk Assessment 1 (QRA1) was published. This was implemented for setting maximum limits for fragrance materials in consumer products. However, there was no formal validation or empirical verification after implementation. Additionally, concerns remained that QRA1 did not incorporate aggregate exposure from multiple product use and included assumptions, e.g. safety assessment factors (SAFs), that had not been critically reviewed. Accordingly, a review was undertaken, including detailed re-evaluation of each SAF together with development of an approach for estimating aggregate exposure of the skin to a potential fragrance allergen. This revision of QRA1, termed QRA2, provides an improved method for establishing safe levels for sensitizing fragrance materials in multiple products to limit the risk of induction of contact allergy. The use of alternative non-animal methods is not within the scope of this paper. Ultimately, only longitudinal clinical studies can verify the utility of QRA2 as a tool for the prevention of contact allergy to fragrance materials.

Application of the dermal sensitization threshold concept to chemicals classified as high potency category for skin sensitization assessment of ingredients for consumer products

Skin sensitization evaluation is a key part of the safety assessment of ingredients in consumer products, which may have skin sensitizing potential. The dermal sensitization threshold (DST) concept, which is based on the concept of the thresholds of toxicological concern, has been proposed for the risk assessment of chemicals to which skin exposure is very low level. There is negligible risk of skin sensitization if a skin exposure level for the substance of interest was below the reactive DST which would protect against 95% of protein-reactive chemicals. For the remaining 5%, the substance with the defined knowledge of chemical structure (i.e., High Potency Category (HPC) rules) needs to be excluded from the application. However, the DST value for HPC chemicals has not yet been proposed. In this study, we calculated the 95th percentile probabilities estimate from distributions of skin sensitization potency data and derived a novel DST for HPC chemicals (HPC DST) of 1.5 μg/cm². This value presents a useful default approach for unidentified substances in ingredients considering, as a worst-case scenario, that the unidentified compound may be a potent skin sensitizer. Finally, we developed a novel risk assessment workflow incorporating the HPC DST along with the previously published DSTs.

Pred-Skin: A Web Portal for Accurate Prediction of Human Skin Sensitizers

Safety assessment is an essential component of the regulatory acceptance of industrial chemicals. Previously, we have developed a model to predict the skin sensitization potential of chemicals for two assays, the human patch test and murine local lymph node assay, and implemented this model in a web portal. Here, we report on the substantially revised and expanded freely available web tool, Pred-Skin version 3.0. This up-to-date version of Pred-Skin incorporates multiple quantitative structure-activity relationship (QSAR) models developed with in vitro, in chemico, and mice and human in vivo data, integrated into a consensus naïve Bayes model that predicts human effects. Individual QSAR models were generated using skin sensitization data derived from human repeat insult patch tests, human maximization tests, and mouse local lymph node assays. In addition, data for three validated alternative methods, the direct peptide reactivity assay, KeratinoSens, and the human cell line activation test, were employed as well. Models were developed using open-source tools and rigorously validated according to the best practices of QSAR modeling. Predictions obtained from these models were then used to build a naïve Bayes model for predicting human skin sensitization with the following external prediction accuracy: correct classification rate (89%), sensitivity (94%), positive predicted value (91%), specificity (84%), and negative predicted value (89%). As an additional assessment of model performance, we identified 11 cosmetic ingredients known to cause skin sensitization but were not included in our training set, and nine of them were accurately predicted as sensitizers by our models. Pred-Skin can be used as a reliable alternative to animal tests for predicting human skin sensitization.

Adjustment of a no expected sensitization induction level derived from Bayesian network integrated testing strategy for skin sensitization risk assessment

Skin sensitization is a key adverse effect to be addressed during hazard identification and risk assessment of chemicals, because it is the first step in the development of allergic contact dermatitis. Multiple non-animal testing strategies incorporating in vitro tests and in silico tools have achieved good predictivities when compared with murine local lymph node assay (LLNA). The binary test battery of KeratinoSens^TM and h-CLAT could be used to classify non-sensitizers as the first part of bottom-up approach. However, the quantitative risk assessment for sensitizing chemicals requires a No Expected Sensitization Induction Level (NESIL), the dose not expected to induce skin sensitization in humans. We used Bayesian network integrated testing strategy (BN ITS-3) for chemical potency classification. BN ITS-3 predictions were performed without a pre-processing step (selecting data from their physic-chemical applicability domains) or post-processing step (Michael acceptor chemistry correction), neither of which necessarily improve prediction accuracy. For chemicals within newly defined applicability domain, all under-predictions fell within one potency class when compared with LLNA results, indicating no chemicals that were incorrectly classified by more than one class. Considering the potential under-prediction by one class, a worst case value to each class from BN ITS-3 was used to derive a NESIL. When in vivo and human data from suitable analogs cannot be used to estimate the uncertainty, adjusting the NESIL derived from BN ITS-3 may help perform skin sensitization risk assessment. The overall workflow for risk assessment was demonstrated by incorporating the binary test battery of KeratinoSens^TM and h-CLAT.

Applying non-animal strategies for assessing skin sensitisation report from an EPAA/cefic-LRI/IFRA Europe cross sector workshop, ECHA helsinki, February 7th and 8th 2019

Four years on since the last cross sector workshop, experience of the practical application and interpretation of several non-animal assays that contribute to the predictive identification of skin sensitisers has begun to accumulate. Non-animal methods used for hazard assessments increasingly are contributing to the potency sub-categorisation for regulatory purposes. However, workshop participants generally supported the view that there remained a pressing need to build confidence in how information from multiple methods can be combined for classification, sub-categorisation and potency assessment. Furthermore, the practical experience gained over the last few years, highlighted the overall high potential value of using the newly validated methods and testing strategies, but also that limitations for certain substance/product classes may become evident with further use as had been the case with other new regulatory methods. As the available information increases, review of the data and collated experience could further determine strengths and limitations leading to more confidence in their use. Finally, the need for a substantial and universally accepted dataset of non-sensitisers and substances of different sensitising potencies, based on combined human and in vivo animal data for validation of methods and test strategies was re-emphasised.

Setting surface wipe limits for skin sensitizers

Guidance for managing potential dermal exposures has historically been qualitative in nature, for example, in the form of a DSEN notation. We propose a method that can provide quantitative guidance on how to establish and use surface wipe limits for skin sensitizers. The murine local lymph node assay (LLNA) is a validated test that not only identifies potential skin sensitizers but also provides an effective concentration (EC3) value. This provides quantitative dose-response information on induction of skin sensitization that permits estimates of sensitization thresholds and potency. Building upon the previously established correlation between LLNA EC3 values and human repeat insult patch testing no-effect levels, we present a quantitative method for setting surface wipe guidelines using the LLNA EC3. These limits can be used to assign compounds to occupational exposure bands and provide handling guidance for skin sensitizers of varying potency, supporting both exposure assessment and control strategies. A table is included that suggests a band of reasonable surface wipe limits (mg/100 cm²) for potentially all chemical sensitizers. When used in conjunction with a comprehensive industrial hygiene program that includes hazard communication, engineering controls, and personal protective equipment, skin exposure and consequent skin sensitization risks in the workplace can be minimized.

Skin Sensitization Induction Potential From Daily Exposure to Fragrances in Personal Care Products

BACKGROUND

Many chemicals used for fragrance purposes in a diversity of products have allergenic potential. Based on such concerns, industry groups developed concentration limits for use of fragrance chemicals in personal care and cosmetic products.

OBJECTIVE

The aim of this study was to use a quantitative risk assessment to evaluate the potential for skin sensitization induction resulting from daily exposure to fragrance chemicals present in personal care and cosmetic products.

METHODS

Product-specific dermal consumer exposure levels were calculated based on product use data in US adult females and benchmarked against acceptable exposure levels based on reported no expected sensitization induction levels to determine a margin of safety for each fragrance under evaluation.

CONCLUSIONS

The results demonstrate an increased risk of skin sensitization induction for several leave-on products (lipstick, solid antiperspirant, eye shadow, face cream) for most of the evaluated fragrance chemicals, particularly under high-use exposure scenarios. In contrast, rinse-off products (shampoo, conditioner, facial cleanser) were not associated with risk of skin sensitization induction. Because the approach was based on maximum use limits for fragrance chemicals with skin sensitization concerns, the results suggest these limits may not be protective, particularly in the United States.

Sensitization to Fragrance mix-1 in Patients with Contact Dermatitis in Nord-East of Italy: 1996–2016 Time Trend and Gender Effect

(1) Background: Fragrance sensitization is common in Italy and their constituents are used in many cosmetics and detergents. The objective of the study was to analyze the temporal trend of sensitivity to fragrance mix-1 in northeastern Italy and to evaluate gender differences; (2) Methods: From 1996 to 2016, 27,381 consecutive patients with suspected allergic contact dermatitis were patch tested. Individual characteristics were collected through a standardized questionnaire in six departments of dermatology or occupational medicine; (3) Results: The overall prevalence of sensitization to fragrance mix-1 was 7.3%; the prevalence was significantly higher in women (7.7%) than in men (6.3%). From 1996 to 2016, we observed an increase of this sensitization, ranging from 6.2% to 7.7% in males and from 7.2% to 9.1% in females; (4) Conclusions: Our study showed that contact allergy to fragrance mix-1 is important in both sexes and prevalence is increasing over time, despite the introduction of new fragrances with lower sensitization potential. There is the need to reduce the use of fragrances mix-1 to stop the increase of sensitization in exposed subjects.

Fragrance inhalation and adverse health effects: The question of causation

The toxicology of fragrance materials is largely well understood. Although most are benign, a minority have the potential to cause adverse health effects, notably allergic contact dermatitis resulting from skin sensitization. As a consequence, industry guidelines have banned certain materials and strictly limited the use of others. Recently, data have been published that have been interpreted to suggest that inhalation of fragrances is associated with the occurrence of a variety of health effects, ranging from headaches to asthma attacks. In this review, the evidence basis for these assertions is examined critically and the biological basis and mechanistic plausibility for causation by fragranced products of these health effects is explored. This review concludes that respiratory effects, including irritation and allergy appear highly unlikely to occur by this route. While some sensory/psychosomatic effects are possible, this does not explain the very high rates of adverse effects reported in the recently published questionnaire studies, which this review concludes are more likely to be attributed to methodological weaknesses. Ultimately, it is concluded that adverse health effects arising from fragrance inhalation are uncommon and remain to be identified and confirmed by methodologically rigorous epidemiological investigations supported by a convincing biological and mechanistic basis.

Skin sensitization: Uncertainties, challenges, and opportunities for improved risk assessment

At the ESCD congress held in Manchester in 2016, a session was organized to encourage more dialogue between clinicians with expertise in skin sensitization and toxicologists seeking to provide effective risk assessment to prevent human health issues. That session focused on the remaining uncertainties regarding the induction and regulation of skin sensitization in humans, and the opportunities and challenges associated with the refinement and improvement of risk assessment methodologies. This short article, prompted by those discussions, debates what the authors regard as being among the most important and most intriguing uncertainties about skin sensitization and allergic contact dermatitis in humans, and the most significant opportunities for improving risk assessment. The aim has been to provide a basis for mapping out the areas that might benefit from a closer alignment between the relevant clinical community and toxicologists charged with the responsibility of ensuring that skin sensitization risks are understood and managed.

The dermal sensitization threshold (DST) approach for mixtures evaluated as negative in in vitro test methods; mixture DST

Cosmetic ingredients often comprise complex mixtures, such as botanical extracts, which may contain skin sensitizing constituents. In our previous study for the sensitivity of the evaluations of skin sensitizing constituents in mixtures using the binary in vitro test battery with KeratinoSens^TM and h-CLAT, some sensitizers showed higher detection limits in in vitro test methods than in murine local lymph node assays (LLNA). Thus, to minimize the uncertainty associated with decreased sensitivity for these sensitizers, a risk assessment strategy was developed for mixtures with negative results from the binary test battery. Assuming that the no expected sensitization induction level of mixtures (mixture NESIL) can be derived for mixtures with negative in vitro test results, we assessed 146 sensitizers with in vitro and LLNA data according to the assumption of indeterminate constituents in mixtures. Finally, we calculated 95th percentile probabilities of mixture NESILs and derived dermal sensitization thresholds for mixtures (mixture DST) with negative in vitro test results of 6010 μg/cm². Feasibility studies indicated that this approach was practical for risk assessments of products in the cosmetic industry. This approach would be a novel risk assessment strategy for incorporating the DST approach and information from in vitro test methods.

Aggregate consumer exposure to isothiazolinones via household care and personal care products: Probabilistic modelling and benzisothiazolinone risk assessment

Consumers regularly use household care and personal care products (HC&PCPs). Isothiazolinones are included in HC&PCPs as preservatives and are being held responsible for an epidemic rise in allergic contact dermatitis (ACD). The objective of this study was to assess the origin and extent of dermal exposure in order to evaluate the risk of ACD from isothiazolinones in HC&PCP. Individual-based aggregate dermal exposure to four isothiazolinones was estimated using the newly proposed Probabilistic Aggregated Consumer Exposure Model-Kinetic, Dermal (PACEM-KD) by combining the reported individual use patterns for HC&PCP in Switzerland (N = 669 (558 adults), ages 0-91) with isothiazolinone concentrations measured in products used by the individual person. PACEM-KD extends the original PACEM by considering exposure duration, product dilution and skin permeability. PACEM-KD-based higher-tier exposure on palms (99th percentile) was 15.4 ng/cm², 1.3 ng/cm², 0.9 ng/cm², and 0.08 ng/cm² for the isothiazolinones 1,2‑Benzisothiazol‑3‑(2H)‑one (BIT), 2‑Octyl‑3(2H)‑isothiazolinone (OIT), 2‑Methylisothiazolin‑3(2H)‑one (MI), and 5‑Chloro‑2‑methyl‑4‑isothiazolin‑3‑one (CMI), respectively. Major sources of exposure to BIT included all-purpose cleaners, dishwashing detergent, and kitchen cleaner, while exposure to OIT mainly stems from a fungicide. For MI, the main contributors were dishwashing detergent and all-purpose wet wipes, and for CMI all-purpose cleaner. A Quantitative Risk Assessment (QRA) for BIT using Sensitization Assessment Factors (SAFs) indicates that around 1% of the Swiss population is at risk to be sensitized by BIT in cosmetics and household chemicals. For isothiazolinones in general the presented higher-tier modelling approach suggests that household cleaners are currently more important sources of exposure than cosmetics.

Health impact assessment of a skin sensitizer: Analysis of potential policy measures aimed at reducing geraniol concentrations in personal care products and household cleaning products

A methodology to assess the health impact of skin sensitizers is introduced, which consists of the comparison of the probabilistic aggregated exposure with a probabilistic (individual) human sensitization or elicitation induction dose. The health impact of potential policy measures aimed at reducing the concentration of a fragrance allergen, geraniol, in consumer products is analysed in a simulated population derived from multiple product use surveys. Our analysis shows that current dermal exposure to geraniol from personal care and household cleaning products lead to new cases of contact allergy and induce clinical symptoms for those already sensitized. We estimate that this exposure results yearly in 34 new cases of geraniol contact allergy per million consumers in Western and Northern Europe, mainly due to exposure to household cleaning products. About twice as many consumers (60 per million) are projected to suffer from clinical symptoms due to re-exposure to geraniol. Policy measures restricting geraniol concentrations to <0.01% will noticeably reduce new cases of sensitization and decrease the number of people with clinical symptoms as well as the frequency of occurrence of these clinical symptoms. The estimated numbers should be interpreted with caution and provide only a rough indication of the health impact.