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Background: p-Phenylenediamine (PPD) is a potent contact allergen found in many hair colour products. However, not all individuals develop allergic contact dermatitis (ACD) although they are regularly exposed to PPD. It is unclear whether these asymptomatic individuals are true non-responders to PPD or whether they mount a response to PPD without showing any symptoms. Methods: Skin biopsies were collected from 11 asymptomatic hairdressers regularly exposed to PPD and from 10 individuals with known ACD on day 4 after patch testing with 1% PPD in petrolatum and petrolatum exclusively as control. RNA sequencing and confocal microscopy were performed. Results: T cell activation, inflammation and apoptosis pathways were up-regulated by PPD in both asymptomatic and allergic individuals. Compared to asymptomatic individuals with a negative patch test, individuals with a strong reaction to PPD strongly up-regulated both pro- and anti-inflammatory cytokines genes. Interestingly, PPD treatment induced significant up-regulation of several genes for chemokines, classical type 2 dendritic cell markers and regulatory T cell markers in both asymptomatic and allergic individuals. In addition, apoptosis signalling pathway was activated in both non-responders and allergic individuals. Conclusion: This study demonstrates that there are no true non-responders to PPD but that the immune response elicited by PPD differs between individuals and can lead to either tolerance, subclinical inflammation or allergy.

Background Occupational contact dermatitis (OCD) is a common occupational disease. Atopic dermatitis (AD) is a known risk factor for OCD. Objectives To determine the prevalence of previously diagnosed AD among young workers with recognized OCD and assess its impact on OCD prognosis. Methods A retrospective cohort study. A questionnaire was sent to 6251 workers with recognized OCD who were under 35 years at notification (response rate: 47%). Of the respondents, 2392 answered a question about previous doctor-diagnosed AD and were included in the study. Eczema severity, occupational consequences and quality of life were examined using statistical analyses comparing workers with and without previously diagnosed AD. Results The prevalence of previously diagnosed AD was 41.8% (95% CI: 39.8–43.8). Women had a higher AD prevalence, and workers with AD reported OCD at a younger age. Workers with AD reported more frequent and severe eczema symptoms and had a higher risk of OCD negatively affecting job and occupation choices. Health-related quality of life was more adversely affected in workers with AD. Conclusions AD significantly impacts severity and has long-term consequences for young people with OCD. Targeted prevention strategies need to be developed., Background: Occupational contact dermatitis (OCD) is a common occupational disease. Atopic dermatitis (AD) is a known risk factor for OCD. Objectives: To determine the prevalence of previously diagnosed AD among young workers with recognized OCD and assess its impact on OCD prognosis. Methods: A retrospective cohort study. A questionnaire was sent to 6251 workers with recognized OCD who were under 35 years at notification (response rate: 47%). Of the respondents, 2392 answered a question about previous doctor-diagnosed AD and were included in the study. Eczema severity, occupational consequences and quality of life were examined using statistical analyses comparing workers with and without previously diagnosed AD. Results: The prevalence of previously diagnosed AD was 41.8% (95% CI: 39.8–43.8). Women had a higher AD prevalence, and workers with AD reported OCD at a younger age. Workers with AD reported more frequent and severe eczema symptoms and had a higher risk of OCD negatively affecting job and occupation choices. Health-related quality of life was more adversely affected in workers with AD. Conclusions: AD significantly impacts severity and has long-term consequences for young people with OCD. Targeted prevention strategies need to be developed.

Background: Rubber accelerators are used in the production of rubber gloves and may cause contact allergy. Objectives: To estimate long-term trend and prevalence of contact allergy to rubber accelerators for a 30-year period in Denmark, high-risk occupations, and exposures. Methods: Data from all patients with contact dermatitis consecutively patch tested at the department of Skin and Allergy Gentofte hospital with the rubber accelerators from the European baseline series (EBS) from 1990 to 2019, were analysed. Further, patients under suspicion of rubber accelerator contact allergy were additionally patch-tested with rubber accelerators from the specialised rubber series from 2005 to 2019 and these were additional extracted. Results: The overall prevalence of contact allergy to one or more of the rubber accelerators from the EBS series was 2.7% with a significant decline in the first 12-years, followed by a stable frequency in the past 18-years. Associations with occupational contact dermatitis, hand dermatitis, and leg/foot dermatitis were found. Wet-work occupations were most often affected and gloves the most frequent exposure. Conclusions: Contact allergy to one or more of the rubber accelerators from the EBS is frequent and has been unchanged for several decades, which calls for prevention.

This systematic review, conducted according to the PRISMA guidelines, focuses on genotoxicity of oxidative hair dye precursors. The search for original papers published from 2000 to 2021 was performed in Medline, Web of Science, Cochrane registry, Scientific Committee on Consumer Safety of the European Commission and German MAK Commission opinions. Nine publications on genotoxicity of p-phenylenediamine (PPD) and toluene-2,5-diamine (p-toluylenediamine; PTD) were included, reporting results of 17 assays covering main genotoxicity endpoints. PPD and PTD were positive in bacterial mutation in vitro assay, and PPD tested positive also for somatic cell mutations in the Rodent Pig-a assay in vivo. Clastogenicity of PPD and PTD was revealed by in vitro chromosomal aberration assay. The alkaline comet assay in vitro showed DNA damage after PPD exposure, which was not confirmed in vivo, where PTD exhibited positive results. PPD induced micronucleus formation in vitro, and increased micronucleus frequencies in mice erythrocytes following high dose oral exposure in vivo. Based on the results of a limited number of data from the classical genotoxicity assay battery, this systematic review indicates genotoxic potential of hair dye precursors PPD and PTD, which may present an important health concern for consumers and in particular for professional hairdressers.

The European baseline series was last updated in 2019. This article discusses the reasoning behind a further iteration of the series for 2023., The European baseline series was last updated in 2019. This article discusses the reasoning behind a further iteration of the series for 2023.

Introduction: Hairdressers are exposed to wet work and manifold allergens at work, rendering exposure complex and the aetiology of occupational hand eczema (OHE) often multifactorial in this occupational group. Objectives: To identify exposure patterns associated with increased risk of hand eczema in hairdressers. Methods: All hairdressers graduating from 2004 to 2007 and 2015 to 2018 received a questionnaire in 2009 and 2020, respectively. Current exposures (with or without regular glove use) and OHE were self-reported, and their association examined. Patterns of exposure were identified by latent class analysis (LCA). Results: A total response of 39.9% (668/1675) was obtained. Six exposure profiles (#1–6) were identified by LCA across 11 tasks performed with or without gloves as well as deep conditioning, that is, 23 task items. Compared to profile #1 with the lowest OHE risk (reference) an increased risk of current OHE were seen in profile #4 [adjusted odds ratio [aOR] 6.5, 95% confidence interval [CI] 1.5–44.8 and #6 (aOR 39.4, 95%CI 6.1–362.8)] in logistic regression analysis. Profile #1 and #6 had performed the same tasks, but in profile #6 regular glove use was performed in 9.1% (1/ 11) of tasks compared to 72.7% (8/11) of tasks in profile #1 (p = 0.002). Conclusion: Although occupational exposures in hairdressing are complex, meaningful patterns associated with a wide range of OHE risk can be identified by LCA. The increase of OHE risk seems predominantly to be due to poor compliance with protective gloves. LCA could be applied to further fields of complex (skin) exposures.

Background: The burden of occupational hand eczema in hairdressers is high, and (partly strong) allergens abound in the hair cosmetic products they use. Objectives: To systematically review published evidence concerning contact allergy to an indicative list of active ingredients of hair cosmetics, namely, p-phenylenediamine (PPD), toluene-2,5-diamine (PTD), persulfates, mostly ammonium persulfate (APS), glyceryl thioglycolate (GMTG), and ammonium thioglycolate (ATG), concerning the prevalence of sensitization, particularly in terms of a comparison (relative risk; RR) between hairdressers and non-hairdressers. Methods: Following a PROSPERO-registered and published protocol, eligible literature published from 2000 to February 2021 was identified, yielding 322 publications, and extracted in standardized publication record forms, also considering risk of bias. Results: Based on 141 publications, the contact allergy prevalence to PPD was 4.3% (95% CI: 3.8–4.9%) in consecutively patch tested patients. Other ingredients were mostly tested in an aimed fashion, yielding variable, and partly high contact allergy prevalences. Where possible, the RR was calculated, yielding an average increased sensitization risk in hairdressers of between 5.4 (PPD) and 3.4 (ATG). Additional evidence related to immediate-type hypersensitivity, experimental results, exposures, and information from case reports was qualitatively synthesized. Conclusions: An excess risk of contact allergy is clearly evident from the pooled published evidence from the last 20 years. This should prompt an improvement in working conditions and product safety.

Occupational hand eczema is frequent in metalworkers. The contribution of metal allergies is poorly elucidated even though such exposures are common at the workplace. To estimate the prevalence of metal allergy to cobalt (Co), chromium (Cr) and nickel (Ni) in metalworkers and compare these to estimates from the European Surveillance System on Contact Allergies (ESSCA). Two authors independently searched PubMed for studies reporting on the prevalence of metal allergy in metalworkers. Proportion meta-analyses were performed to calculate the pooled proportions of metal allergy in metalworkers. In total, 29 studies (22 from Europe) were included yielding 5691 subjects for quantitative analysis. The pooled proportion (95% confidence interval) of Co, Cr and Ni in European metalworkers with dermatitis referred to patch test clinics was 8.2% (5.3%–11.7%), 8.0% (5.1%–11.4%), and 11.0% (7.3%–15.4%), respectively. The corresponding estimates for unselected metalworkers from workplace studies were 4.9% (2.4%–8.1%), 5.2% (1.0%–12.6%), and 7.6% (3.8%–12.6%), respectively. In comparison, the prevalence of metal allergy in 13 382 consecutive European males with dermatitis was 3.9% (3.6%–4.2%), 4.4% (4.1%–4.8%) and 6.7% (6.3%–7.0%) for Co, Cr and Ni, respectively. Data on sex, age, body piercings and atopic dermatitis in metalworkers with metal allergy was mostly lacking. Metal allergy to all three metals was significantly more common in European metalworkers with dermatitis attending patch test clinics as compared to ESSCA data, indicating a relationship to occupational exposures, however, confounders could not be accounted for.

Artificial nail modelling systems (ANMS), encompassing artificial nails and long-lasting nail polish, are sources of acrylate exposure in beauticians and users of ANMS. Hairdressers’ exposure to ANMS from self-use and occupational exposure is currently unknown. In 2020 a questionnaire was sent to all hairdressers graduating during 2008 to 2018 in Denmark (n = 4,830). Self-use of ANMS was reported by 87.6% of respondents (1,251/1,428), and application of ANMS to others was reported by 22.1% (316/1,428). Of these, application to others was performed in a salon by 37.1% (109/294), privately by 51.0% (150/294) and in both settings by 11.9% (35/294). Compliance with glove use was seen in 23.0% (67/291) among those applying ANMS to others. Among hairdressers exposed to ANMS, 4.3% (52/1,218) reported ANMS-related hand eczema. Be-ing a trained beautician (adjusted odds ratio 3.26, 95% confidence interval 1.06–9.99) and having had a positive patch-test to acrylates (adjusted odds ratio 7.70, 95% confidence interval 1.44–41.13) were associated with ANMS-related hand dermatitis. In conclu-sion, hairdressers have a high prevalence of exposure to ANMS and ANMS-related hand dermatitis. Compliance with glove use when applying ANMS to others is poor. Patch-testing with acrylates is valuable in the diagnostic work-up of hand eczema in hairdressers.

Background: Parents report that children with aluminium contact allergy and vaccination granulomas may react to aluminium-containing sunscreen following application. Objectives: To evaluate whether contact dermatitis develops following repeated application of aluminium-containing sunscreens in children with aluminium sensitization and vaccination granulomas. Methods: Sixteen children aged 2-9 years (mean age 5 years) with vaccination granulomas and a positive patch test reaction to aluminium chloride hexahydrate 2%/10% petrolatum completed a blinded repeated open application test (ROAT) with two daily applications of two sunscreens for 14 days. One cream contained aluminium and the other did not. The children served as their own controls. Results: Sixteen children completed the study. Only one child (6%) had a positive skin reaction during ROAT on day 2 to the sunscreen with aluminium. None reacted to the sunscreen without aluminium. Conclusions: Use of aluminium-containing sunscreens may on a case basis lead to allergic contact dermatitis in aluminium allergic children.

OBJECTIVES: To review recent epidemiological studies investigating carcinogenic or reprotoxic effects among hairdressers who seem to be at greater risk for systemic adverse effects of chemicals released from hair care products than consumers. METHODS: A systematic review according to the PRISMA-P guidelines was performed and included studies published from 2000 to August 2021, in which cancer or adverse reproductive effects were diagnosed in 1995 and onward. Data were synthetized qualitatively due to the small number of studies, heterogeneity of study designs, outcomes, and methods. RESULTS: Four studies investigating cancer frequencies and six studies investigating effects on reproduction among hairdressers were identified. All were of good quality and with low risk of bias. Only one of the four studies found an increased risk of cancer reporting nine times higher odds for bladder cancer in hairdressers than the population-based controls. Three other studies investigating bladder and lung cancer, and non-Hodgins lymphoma did not find an increased risk in hairdressers. Regarding reprotoxic effects, numerous outcomes were investigated including menstrual disorders, congenital malformations, fetal loss, small-for-gestational age newborns, preterm delivery, and infertility. Increased risk was found for ventricular septal defect in newborns of fathers working as hairdressers. Furthermore, several indices of poor neonatal or maternal health were significantly associated with mothers working as hairdresser. CONCLUSIONS: Despite the scarce evidence that hairdressers are at increased risk of carcinogenic or reprotoxic effects related to their trade, such health risks cannot be ruled out. Therefore, preventive efforts to diminish occupational exposures to hairdressing chemicals should be targeted.

Background Compliance with glove use and safe work practices are important factors in primary prevention of occupational hand eczema (OHE) in hairdressers. Objective To assess the risk OHE and compliance with skin protective measures in hairdressers trained before and after implementation of a nationwide skin protection program in Danish hairdressing vocational schools in 2011. Methods A repeated cross-sectional study was performed. A questionnaire was sent in 2009 and 2020. The Danish Labour Market Supplementary Pension Scheme provided information on yearly payments from the hairdressing profession. Results A response rate of 66.6% (305/460) was obtained in the 2009 survey and of 29.9% (363/1215) in the 2020 survey. The career time prevalence of OHE decreased from 42.8% to 29.0% (adjusted odds ratio 0.55 95% confidence interval [CI] 0.40-0.77) and the incidence rate of OHE decreased from 57.5 (95%CI 48.4-68.4) to 42.0 (95%CI 34.6-50.9) per 1000 person years (incidence rate ratio 0.73 [95%CI 0.56-0.95] between the two surveys). A statistically significant (P < .05) increase in glove use when doing wet-work and when handling hair dyes, permanent wave solutions and bleaching products was observed in the 2020 compared to the 2009 survey. Conclusion Our data suggest that skin protection training during apprenticeship reduces the risk of OHE in hairdressers. The lack of primary prevention of OHE in hairdressing vocational schools may be a missed opportunity in the prevention of the disease.

Background: Studies on the causes and consequences of occupational contact dermatitis (OCD) among young workers are non-existent. Objectives: Determine causes and consequences of OCD among workers younger than 35 years of age. Methods: A questionnaire was sent to 6251 workers younger than 35 years at notification with recognized OCD (response rate 47%). Results: The most prevalent occupations were health care workers, kitchen workers, nursery teachers, and hairdressers and beauticians. Seventy-six percent still had eczema, and 77% of these had eczema half to all the time over the last 3 months, with 61% evaluating their eczema as moderate to very severe. Fifty-three percent had changed their occupation since notification, and 42.5% had lost their job because of OCD. Allergic OCD increased the odds ratio (OR) for facial or foot eczema, job loss, change in work tasks, difficulties finding work, decrease in income, and sick leave. Age at notification of 25 years of age or younger increased the risk of job loss and feeling restricted in choice of job. Workers in the food industry had a higher OR for job loss, whereas hairdressers and beauticians had a higher risk of job loss and a decrease in income. Conclusions: The severe, long-term consequences of OCD notification signify the need for further preventive strategies among young workers.

Objective: To review the literature on respiratory effects of persulfate salts (PS) or hair bleaches in hairdressers and animal models exploring mechanisms behind PS-induced asthma. Methods: A systematic review according to the PRISMA guidelines was performed. Studies published from 2000 to July 2021 that fulfilled predefined eligibility criteria were retrieved. Data were not quantitatively synthesized due to the heterogeneity of study designs, outcomes and methods. Results: Forty-two articles were included. PS are indicated as the main cause of occupational rhinitis and asthma in hairdressers, and one of the leading causes of occupational asthma in some European countries. Bleaching products are indicated as the most important factor for development of respiratory symptoms, lung function decline, and leaving the hairdressing profession. Risk estimates from a good quality prospective study showed up to 3.9 times higher risk for wheezing and breathlessness in hairdressers aged ≥ 40 years than in matched controls, and 20 times higher risk in hairdressers to develop respiratory symptoms from exposure to bleaching powder than controls. Pathophysiological mechanisms of the respiratory response to PS are not yet fully elucidated, but may include non-specific and specific immune responses. Conclusions: Hairdressing is associated with a wide spectrum of respiratory adverse effects, of which bleaching products were indicated as the most hazardous. Preventive measures for reducing inhalatory exposure to PS in hair salons should be re-evaluated, including adopting occupational exposure limits at EU level, and encouraging use of safer bleach formulations. PROSPERO registration number: CRD42021238118.

Introduction: Exposure to hazardous chemicals released during hairdressing activities from hair care products puts hairdressers at risk of adverse health effects. Safety assessments of hair products are mainly focused on consumers, but exposure for professional hairdressers might be substantially higher. Objective: To identify and assess available research data on inhalation exposures of professional hairdressers. Methods: A systematic search of studies between 1 January 2000 and 30 April 2021 was performed in Medline, Embase, Web of Science and in Cochrane registry, toxicological dossiers of the Scientific Committee on Consumer Safety (SCCS) of the European Commission as well as the German MAK Commission. Studies reporting quantitative data on airborne concentrations of chemicals in the hairdresser’s workplace were considered. The outcome was an airborne concentration of chemicals in the working environment, which was compared, when possible, with current occupational exposure limits (OEL) or guidance levels. Results: In total, 23 studies performed in 14 countries were included. The average number of hairdressing salons per study was 22 (range 1–62). Chemicals most frequently measured were formaldehyde (n = 8), ammonia (n = 5), total volatile organic compounds (TVOC) (n = 5), and toluene (n = 4). More than fifty other chemicals were measured in one to three studies, including various aromatic and aliphatic organic solvents, hydrogen peroxide, persulfate, and particulate matter. Most studies reported environmental air concentrations, while personal exposure was measured only in seven studies. The measured air concentrations of formaldehyde, ammonia, and TVOC exceeded OEL or guidance values in some studies. There was large variability in measuring conditions and reported air concentrations differed strongly within and between studies. Conclusion: Hairdressers are exposed to a wide spectrum of hazardous chemicals, often simultaneously. Airborne concentrations of po

In Germany, a stepwise multidisciplinary approach has been established to prevent occupational skin diseases (OSDs), primarily occupational contact dermatitis. This review aims to perform a systematic evaluation of the short- and long-term effects of the German secondary and tertiary individual prevention programmes (SIP and TIP, respectively) for OSDs. Primary outcomes were continuation of employment, severity of hand dermatitis, and quality of life (QoL). The PubMed and Embase databases were searched for studies reporting the effects of the SIP and TIP. A total of 19 studies encompassing 5527 patients with OSDs were included: 11 studies evaluated the SIP and 8 evaluated the TIP. Following the SIP, approximately 70% to 90% and 60% to 70% of patients remained in their occupation after 1 and 5 years, respectively. At 3 years after the TIP, 82.7% of patients remained in their occupation and exhibited a significant decrease in hand dermatitis severity, as well as an increase in QoL. Most of these studies were uncontrolled and the interventions, outcomes, and measurement instruments used were heterogeneous. The SIP and TIP lead to decreased disease severity, improved QoL, and enabled most patients to continue working in their chosen professions. Implementing a similar multidisciplinary approach across Europe may be beneficial.

Background: No biomarkers have been identified that can classify subtypes of hand eczema (HE). Although skin biopsies represent the gold standard for investigations of the skin, the invasive technique is not favorable when investigating skin from sensitive areas. Recent advances in the use of skin-tape strips for molecular investigations enable noninvasive investigations of HE. Objective: By using whole transcriptome sequencing (WTS), the molecular profile of HE according to different localizations on the hands, etiologies, and clinical/morphological subtypes was investigated. Methods: Thirty adult, Danish HE patients, 12 with and 18 without concurrent atopic dermatitis (AD), as well as 16 controls were included. Tape strip samples were collected from lesional, nonlesional, and healthy skin. Total RNA was extracted and WTS was performed. Results: The largest molecular difference of HE patients with and without AD was found in nonlesional skin areas and included a downregulation of CXCL8 for HE patients without AD. Differences between allergic and irritant contact dermatitis included promising epidermal biomarkers such as EPHA1. Conclusion: Skin tape strip samples could be used to assess the gene expression profile of HE on different localizations of the hands. The skin tape strip method identified new molecular markers that showed promising result for the identification of HE subtypes.

Background: Hairdressers are commonly affected by hand eczema (HE) due to skin hazardous exposure such as irritants and allergens in the work environment. Objective: To give an overview of the current prevalence, incidence, and severity, as well as the pattern of debut and the contribution of atopic dermatitis on HE in hairdressers. Methods: A systematic review according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines was performed. Studies published from 2000 to April 2021 that fulfilled predefined eligibility criteria were retrieved. Results: A pooled lifetime prevalence of 38.2% (95% confidence interval [CI] 32.6-43.8), a pooled 1-year prevalence of 20.3% (95% CI 18.0-22.6), and a pooled point prevalence of 7.7% (95% CI 5.8-9.6) of HE was observed in hairdressers. The lifetime prevalence in fully trained hairdressers and hairdressing apprentices was almost identical. The pooled incidence rate of HE was 51.8 cases/1000 person-years (95% CI 42.6-61.0) and the pooled prevalence of atopic dermatitis was 18.1% (95% CI 13.6-22.5). Conclusion: HE is common in hairdressers and most hairdressers have debut during apprenticeship. The prevalence of atopic dermatitis in hairdressers is comparable with estimates in the general population, indicating that occupational exposures are the main factor in the increased prevalence of HE in hairdressers. This warrants a strategic and collective effort to prevent HE in hairdressers.

Current cosmetic regulations primarily focus on protecting consumers, not the professional user who is subjected to a partly different, and certainly more intense exposure to hazardous substances. Against this background, this systematic review aims to compile and appraise evidence regarding skin toxicity of 2-hydroxyethyl methacrylate (HEMA; CAS no. 212-782-2) and ethyl cyanoacrylate (ECA; CAS no. 7085-85-0) contained in cosmetic glues used among hairdressers and beauticians who perform nail treatments and eyelash extension as well as hair extension applications. This systematic review followed the Preferred Reporting Items for Systematic review and Meta-Analysis (PRISMA) 2020 recommendations for reporting systematic reviews and meta-analysis. In total, six publications from six countries were eligible for this systematic review. A meta-analysis revealed that hairdressers and beauticians have a ninefold increased risk of developing contact allergy to HEMA compared with controls who are not hairdressers and beauticians. Results for ECA are lacking. The results of this systematic review clearly show that—regarding contact allergy to acrylates—it is not appropriate to apply risk assessment for consumers to hairdressers and beauticians who occupationally handle cosmetic glues. The regulations in existence do not adequately address occupational risks for hairdressers and beauticians connected with the use of acrylate-containing cosmetic substances and need reconsideration.

Hairdressers are at high risk of developing occupational hand eczema. Opinions on the health and safety concerns of nonfood consumer products, such as cosmetics and their ingredients, consider the exposure of a “common consumer,” which may not account for occupational exposure of hairdressers. As a result, there is a parlous scenario in which serious safety concerns about occupational exposures are present. The purpose of this review is to compare the frequency of exposure to various types of hair cosmetic products among hairdressers and consumers. Database searches for this review yielded a total of 229 articles; 7 publications were ultimately included. The analysis showed that—dependent on the task—hairdressers were exposed 4 to 78 times more than consumers to a wide spectrum of hair cosmetic products used in their daily working life, ranging from shampoos, conditioners, oxidative and nonoxidative hair colors, to bleaching agents. The highest frequency was found for coloring hair with oxidative hair color. Consumer use frequency does not appear to be appropriate for representing hairdresser exposure. The current standards do not effectively address the occupational risks associated with hairdressers' use of cosmetics. The findings of this study should cause current risk-assessment procedures to be reconsidered.

Background: Allergic contact dermatitis (ACD) is classically described as a delayed-type hypersensitivity reaction. However, patients often experience flare-ups characterized by itching erythema, edema, and often vesicles occurring within hours after re-exposure of previously sensitized skin to the specific contact allergen. Recent studies have indicated that skin-resident memory T (TRM) cells play a central role in ACD. However, the pathogenic role of TRM cells in allergen-induced flare-ups is not known. Methods: By the use of various mouse models and cell depletion protocols, we investigated the role of epidermal TRM cells in flare-up reactions to the experimental contact allergen 1-fluoro-2,4-dinitrobenzene. The inflammatory response was measured by changes in ear thickness, and the cellular composition in epidermis was determined by flow cytometry and confocal microscopy. Finally, adaptive transfer and inhibitors were used to determine the role of TRM cells, neutrophils, and CXCL1/CXCL2 in the response. Results: We show that CD8+ TRM cells initiate massive infiltration of neutrophils in the epidermis within 12 h after re-exposure to the contact allergen. Depletion of neutrophils before re-exposure to the allergen abrogated the flare-up reactions. Furthermore, we demonstrate that CD8+ TRM cells mediate neutrophil recruitment by inducing CXCL1 and CXCL2 production in the skin, and that blockage of the C-X-C chemokine receptor type 1 and 2 inhibits flare-up reactions and neutrophil infiltration. Conclusion: As the first, we show that epidermal CD8+ TRM cells cause ACD flare-ups by rapid recruitment of neutrophils to the epidermis.