Intestinal Barrier Healing Is Superior to Endoscopic and Histologic Remission for Predicting Major Adverse Outcomes in Inflammatory Bowel Disease: The Prospective ERIca Trial.

BACKGROUND & AIMS: Endoscopic and histologic remission have emerged as key therapeutic goals in the management of inflammatory bowel diseases (IBD) that are associated with favorable long-term disease outcomes. Here, we prospectively compared the predictive value of barrier healing with endoscopic and histologic remission for predicting long-term disease behavior in a large cohort of patients with IBD in clinical remission. METHODS: At baseline, patients with IBD in clinical remission underwent ileocolonoscopy with assessment of intestinal barrier function by confocal endomicroscopy. Endoscopic and histologic disease activity, as well as barrier healing, was prospectively assessed along established scores. During subsequent follow-up, patients were closely monitored for clinical disease activity and the occurrence of major adverse outcomes (MAOs): disease flares, IBD-related hospitalization or surgery, and initiation or dose escalation of systemic steroids, immunosuppressants, small molecules, or biological therapy. RESULTS: The final analysis included 181 patients, 100 with Crohn's disease [CD] and 81 with ulcerative colitis (UC). During a mean follow-up of 35 (CD) and 25 (UC) months, 73% of patients with CD and 69% of patients with UC experienced at least 1 MAO. The probability of MAO-free survival was significantly higher in patients with IBD with endoscopic remission compared with endoscopically active disease. In addition, histologic remission predicted MAO-free survival in patients with UC but not CD. Barrier healing on endomicroscopy was superior to endoscopic and histologic remission for predicting MAO-free survival in both UC and CD. CONCLUSIONS: Barrier healing is associated with decreased risk of disease progression in patients with clinically remittent IBD, with superior predictive performance compared with endoscopic and histologic remission. Analysis of barrier function might be considered as a future treatment target in clinical trials. CLINICALTRIALS: gov number, NCT05157750.

Contact sensitization to fragrance mix I and fragrance mix II among European dermatitis patients: A systematic review.

BACKGROUND: Fragrance substances are a frequent cause of contact allergy worldwide. Fragrance exposure varies by sex, age and possibly country, influenced by cosmetic availability, environmental conditions and cultural practices. OBJECTIVES: To systematically review and gather prevalence of sensitization to fragrance mix I (FM I) and fragrance mix II (FM II) in consecutively patch-tested European dermatitis patients. METHOD: A total of 4134 publications on patch test results of European dermatitis patients, published from 1981 to 2022, were systematically reviewed according to a previously registered and published PROSPERO protocol. RESULTS: Eighty-four eligible original articles were analysed. Overall prevalence of sensitization to fragrance mix I (FM I) was 6.81% (95% CI: 6.37-7.28), and FM II was 3.64% (95% CI: 3.3-4.01). Sensitization to FM I was most prevalent in Central and Eastern Europe and to FM II in Western Europe. No clear time trends were observed. Among paediatric dermatitis patients, sensitization prevalence for FM I and FM II was 4.09% (95% CI: 3.37-4.96) and 2.17% (95% CI: 1.53-3.07). CONCLUSION: The frequency of positive patch test results for both FMI and FMII remains high. Sensitization is also prevalent among children. Enhanced regulation and labelling of cosmetic products play a vital role in averting exposure and sensitization to fragrance allergens.

Declining frequency of sensitization to fragrance mixes I and II: IVDK-data of the years 2012-2021.

BACKGROUND: EU Commission Regulation 2017/1410 prohibits using atranol and chloroatranol, the main allergens in Evernia prunastri (oakmoss), and hydroxyisohexyl 3-cyclohexene carboxaldehyde (HICC) in cosmetic products. Oakmoss absolute is contained in fragrance mix (FM) I and HICC in FM II which are patch tested as screening mixtures in the baseline series. OBJECTIVE: To describe the time trends of reaction frequencies to both FMs as well as to their components in FM-positive patients. METHODS: Retrospective analysis of data from the Information Network of Departments of Dermatology (IVDK), 2012-2021. RESULTS: Positive reactions to FM I (FM II) declined from 9.1% (4.7%) in 2012 to 4.6% (3.0%) in 2021. Full breakdown tests were performed in 24% (FM I) and 31% (FM II), respectively, of the mix-positive patients. From this data, frequencies of sensitization to the 14 single fragrances of FM I and FM II were calculated. For the majority, a decline was noted from 2012/2013 to 2020/2021, for oakmoss absolute 1.9%-0.8% and for HICC 1.8%-0.9%. CONCLUSION: EU Commission Regulation 2017/1410 was an effective measure. However, our data have some limitations, possibly causing underestimation of sensitization frequencies to fragrances.

Results of patch testing with five fragrance materials hitherto not tested: A dose-finding study in the clinical population.

BACKGROUND: Quantitative risk assessment (QRA) for skin sensitization is used to derive safe use levels of sensitising fragrance ingredients in products. Post-marketing surveillance of the prevalence of contact allergy to these ingredients provides relevant data to help evaluate the performance of these measures. OBJECTIVES: To determine a suitable patch test concentration for five fragrance materials that had hitherto not been tested on a regular basis. These concentrations are then to be used in a surveillance study with patch testing consecutive patients over an extended monitoring period. MATERIALS AND METHODS: Furaneol, CAS.3658-77-3; trans-2-hexenal, CAS.6728-26-3; 4,8-dimethyl-4,9-decadienal, CAS.71077-31-1; longifolene, CAS.475-20-7; benzaldehyde, CAS.10052-7, were patch tested with other fragrance allergens in four clinics. Patch testing was conducted in three rounds, starting with the lowest concentrations of the five ingredients. The doses were increased in the subsequent rounds if no late-appearing positive reactions and virtually no irritant reactions were reported. RESULTS: Overall, 373 patients were tested. No positive allergic reaction was reported to the five ingredients. Patch test results of other fragrance allergens are reported. CONCLUSIONS: The highest test concentrations are each considered safe for patch testing consecutive patients. Further surveillance based on these preparations will evaluate the hypothesis that QRA-driven consumer product levels of these fragrances can prevent sensitization.

Severely compromised supply of patch test allergens in Europe hampers adequate diagnosis of occupational and non-occupational contact allergy. A European Society of Contact Dermatitis (ESCD), European Academy of Allergy and Clinical Immunology (EAACI), European Academy of Dermatology and Venereology (EADV) task forces 'Contact Dermatitis' and 'Occupational Skin Disease' position paper.

Patch testing is the only clinically applicable diagnostic method for Type IV allergy. The availability of Type IV patch test (PT) allergens in Europe, however, is currently scarce. This severely compromises adequate diagnostics of contact allergy, leading to serious consequences for the affected patients. Against this background, the European Society of Contact Dermatitis (ESCD) has created a task force (TF) (i) to explore the current availability of PT substances in different member states, (ii) to highlight some of the unique characteristics of Type IV vs. other allergens and (iii) to suggest ways forward to promote and ensure availability of high-quality patch testing substances for the diagnosis of Type IV allergies throughout Europe. The suggestions of the TF on how to improve the availability of PT allergens are supported by the ESCD, the European Academy of Allergy and Clinical Immunology, and the European Academy of Dermatology and Venereology and intend to provide potential means to resolve the present medical crisis.

Accelerated partial breast irradiation using sole interstitial multicatheter brachytherapy compared with whole-breast irradiation with boost for early breast cancer: 10-year results of a GEC-ESTRO randomised, phase 3, non-inferiority trial.

BACKGROUND: Several randomised, phase 3 trials have investigated the value of different techniques of accelerated partial breast irradiation (APBI) for patients with early breast cancer after breast-conserving surgery compared with whole-breast irradiation. In a phase 3 randomised trial, we evaluated whether APBI using multicatheter brachytherapy is non-inferior compared with whole-breast irradiation. Here, we present the 10-year follow-up results. METHODS: We did a randomised, phase 3, non-inferiority trial at 16 hospitals and medical centres in Austria, Czech Republic, Germany, Hungary, Poland, Spain, and Switzerland. Patients aged 40 years or older with early invasive breast cancer or ductal carcinoma in situ treated with breast-conserving surgery were centrally randomly assigned (1:1) to receive either whole-breast irradiation or APBI using multicatheter brachytherapy. Whole-breast irradiation was delivered in 25 daily fractions of 50 Gy over 5 weeks, with a supplemental boost of 10 Gy to the tumour bed, and APBI was delivered as 30·1 Gy (seven fractions) and 32·0 Gy (eight fractions) of high-dose-rate brachytherapy in 5 days or as 50 Gy of pulsed-dose-rate brachytherapy over 5 treatment days. Neither patients nor investigators were masked to treatment allocation. The primary endpoint was ipsilateral local recurrence, analysed in the as-treated population; the non-inferiority margin for the recurrence rate difference (defined for 5-year results) was 3 percentage points. The trial is registered with ClinicalTrials.gov, NCT00402519; the trial is complete. FINDINGS: Between April 20, 2004, and July 30, 2009, 1328 female patients were randomly assigned to whole breast irradiation (n=673) or APBI (n=655), of whom 551 in the whole-breast irradiation group and 633 in the APBI group were eligible for analysis. At a median follow-up of 10·36 years (IQR 9·12-11·28), the 10-year local recurrence rates were 1·58% (95% CI 0·37 to 2·8) in the whole-breast irradiation group and 3·51% (1·99 to 5·03) in the APBI group. The difference in 10-year rates between the groups was 1·93% (95% CI -0·018 to 3·87; p=0·074). Adverse events were mostly grade 1 and 2, in 234 (60%) of 393 participants in the whole-breast irradiation group and 314 (67%) of 470 participants in the APBI group, at 7·5-year or 10-year follow-up, or both. Patients in the APBI group had a significantly lower incidence of treatment-related grade 3 late side-effects than those in the whole-breast irradiation group (17 [4%] of 393 for whole-breast irradiation vs seven [1%] of 470 for APBI; p=0·021; at 7·5-year or 10-year follow-up, or both). At 10 years, the most common type of grade 3 adverse event in both treatment groups was fibrosis (six [2%] of 313 patients for whole-breast irradiation and three [1%] of 375 patients for APBI, p=0·56). No grade 4 adverse events or treatment-related deaths have been observed. INTERPRETATION: Postoperative APBI using multicatheter brachytherapy after breast-conserving surgery in patients with early breast cancer is a valuable alternative to whole-breast irradiation in terms of treatment efficacy and is associated with fewer late side-effects. FUNDING: German Cancer Aid, Germany.

Diagnostics and Prevention of Occupational Allergy in Hairdressers.

PURPOSE OF REVIEW: This study aims to provide an overview on current knowledge on occupational allergic diseases in hairdressers and up-to-date perspectives of prevention. RECENT FINDINGS: Hand eczema (dermatitis) is common in hairdressers, often caused by contact allergy to one or multiple small molecules (haptens) used, e.g., for dyeing, bleaching, and waving/relaxing or by ancillary substances such as preservatives. Hairdressers, compared to other patch-tested patients, have an up to fivefold increased risk to be found sensitized, e.g., against p-phenylenediamine, ammonium persulfate, and glyceryl thioglycolate. Some of these small molecules may induce respiratory sensitization causing allergic rhinitis and/or asthma, notably persulfate salts. Occupational hazards in hairdressing are well described. This knowledge needs to be put into use for risk reduction, mainly by substitution of allergenic ingredients by less allergenic ones, education, and use of ventilation and suitable single-use gloves.

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.

SCCS scientific opinion on Butylated hydroxytoluene (BHT) - SCCS/1636/21.

OPINION TO BE CITED AS: SCCS (Scientific Committee on Consumer Safety), scientific opinion on Butylated hydroxytoluene (BHT), preliminary version of September 27, 2021, final version of December 2, 2021, SCCS/1636/21.

SCCS Scientific Opinion on Acid Yellow 3 (submission II) - SCCS/1631/21.

Opinion to be cited as: SCCS (Scientific Committee on Consumer Safety), Opinion on Acid Yellow 3 - C054 (CAS Number 8004-92-0, EC No 305-897-5), submission II, preliminary version of 7 May 2021, final version of 23 July 2021, SCCS/1631/21.

Bleaching powders, bleaching creams and other hair lightening preparations as sources for (airborne) allergic contact dermatitis and other health effects in hairdressers: Results of an empirical study.

BACKGROUND: Various products are available for lightening hair. There are no data on which applications are actually used in hairdressing, impeding proper estimation of actual exposure and necessary preventive measures. OBJECTIVES: To assess information about availability, usage and formulation of lightening preparations in the German hairdressing trade. METHODS: A market survey was conducted and hairdressers were surveyed by online questionnaires. RESULTS: Of 783 hairdressers clicking the link, 565 hairdressers (91.2% female, mean age of 40.2 ± 11.7 years) from all German states responded (response rate: 72.2%). The questionnaire survey has shown that available hair-lightening preparations in the German hairdressing trade are (multiple selection possible): dust-free (88.5%) and non-dust-free bleaching powders (22.1%), bleaching creams (41.9%), high-lifting hair colour creams (88.8%) and normal hair colour creams (58.4%). Five hundred eighteen (91.7%) hairdressers favour lightening hair with powder. The market survey revealed that bleaching powders and creams contain potassium persulfate, ammonium persulfate and sodium persulfate or combinations of these persulfate salts. CONCLUSIONS: Hairdressers are exposed to various hair-lightening applications containing different chemicals. Preventive measures need to address adverse skin and respiratory effects. Implementation of targeted health education already in early career stages (i.e., apprenticeship) seems advisable and can be maintained by refresher trainings.

Aetiology of occupational hand eczema in hairdressers: Tackling the complexity of exposure combinations to identify patterns associated with increased risk of hand eczema.

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.

Contact allergy to ingredients of hair cosmetics in female hairdressers and female consumers-An update based on IVDK data 2013-2020.

BACKGROUND: Hair cosmetic products contain several, partly potent contact allergens, including excipients like preservatives. Hand dermatitis in hairdressers is common, scalp and face dermatitis in clients or self-users (summarised here as 'consumers') may be severe. OBJECTIVE: To compare frequencies of sensitization to hair cosmetic ingredients and other selected allergens between female patch tested patients working as hairdressers and consumers without professional background, respectively, who were tested for suspected allergic contact dermatitis to such products. METHODS: Patch test and clinical data collected by the IVDK (https://www.ivdk.org) between 01/2013 and 12/2020 were descriptively analysed, focusing on age-adjusted sensitization prevalences in the two subgroups. RESULTS: Amongst the 920 hairdressers (median age: 28 years, 84% hand dermatitis) and 2321 consumers (median age: 49 years, 71.8% head/face dermatitis), sensitization to p-phenylenediamine (age-standardised prevalence: 19.7% and 31.6%, respectively) and toluene-2,5-diamine (20 and 30.8%) were most common. Contact allergy to other oxidative hair dye ingredients was also more commonly diagnosed in consumers, whereas ammonium persulphate (14.4% vs. 2.3%) and glyceryl thioglycolate (3.9 vs. 1.2%) as well as most notably methylisothiazolinone (10.5% vs. 3.1%) were more frequent allergens in hairdressers. CONCLUSIONS: Hair dyes were the most frequent sensitizers both in hairdressers and in consumers; however, as indication for patch testing may differ, prevalences cannot directly be compared. The importance of hair dye allergy is evident, often with marked coupled reactivity. Workplace and product safety need to be further improved.

The European baseline series and recommended additions: 2023.

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

Systematic review on skin adverse effects of important hazardous hair cosmetic ingredients with a focus on hairdressers.

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 contact allergy: The European perspective-Analysis of patch test data from ESSCA between 2011 and 2020.

BACKGROUND: Occupational skin diseases have led the occupational disease statistics in Europe for many years. Especially occupational allergic contact dermatitis is associated with a poor prognosis and low healing rates leading to an enormous burden for the affected individual and for society. OBJECTIVES: To present the sensitization frequencies to the most relevant allergens of the European baseline series in patients with occupational contact dermatitis (OCD) and to compare sensitization profiles of different occupations. METHODS: The data of 16 022 patients considered having OCD after patch testing within the European Surveillance System on Contact Allergies (ESSCA) network between January 2011 and December 2020 were evaluated. Patients (n = 46 652) in whom an occupational causation was refuted served as comparison group. RESULTS: The highest percentages of OCD were found among patients working in agriculture, fishery and related workers, metal industry, chemical industry, followed by building and construction industry, health care, food and service industry. Sensitizations to rubber chemicals (thiurams, carbamates, benzothiazoles) and epoxy resins were associated with at least a doubled risk of OCD. After a decline from 2014 onwards, the risks to acquire an occupation-related sensitization to methyl(chloro)isothiazolinone (MCI/MI) and especially to methylisothiazolinone (MI) seem to increase again. Sensitization rates to formaldehyde were stable, and to methyldibromo glutaronitrile (MDBGN) slightly decreasing over time. CONCLUSIONS: Among allergens in the European Baseline Series, occupational relevance is most frequently attributed to rubber accelerators, epoxy resins and preservatives.

Novel insights into contact dermatitis.

Contact dermatitis is a common disease that is caused by repeated skin contact with contact allergens or irritants, resulting in allergic contact dermatitis (ACD) and/or irritant contact dermatitis. Attempts have been made to identify biomarkers to distinguish irritant and allergic patch test reactions, which could aid diagnosis. Some promising candidates have recently been identified, but verification and validation in clinical cases still need to be done. New causes of ACD are constantly being recognized. In this review, 10 new contact allergens from recent years, several relating to anti-aging products, have been identified. Frequent allergens causing considerable morbidity in the population, such as the preservative methylisothiazolinone, have been regulated in the European Union. A significant drop in the number of cases has been seen, whereas high rates are still occurring in other areas such as North America. Other frequent causes are fragrance allergens, especially the widely used terpenes and acrylates found in medical devices for control of diabetes. These represent unsolved problems. Recent advances in immunology have opened the way for a better understanding of the complexity of contact dermatitis, especially ACD-a disease that may be more heterogenous that previous understood, with several subtypes. With the rapidly evolving molecular understanding of ACD, the potential for development of new drugs for personalized treatment of contact dermatitis is considerable.

Occupational hand eczema reduces career length in hairdressers: a prospective cohort study of Danish hairdressers graduating from 1985 to 2007.

BACKGROUND: Occupational hand eczema (OHE) is common in hairdressers, and many leave the trade because of the disease. However, the exact impact of OHE on career length is unknown. OBJECTIVE: To assess the effect of OHE on career length and risk factors associated with leaving the trade because of OHE in hairdressers followed-up for up to 35 years. METHODS: A prospective cohort study of Danish hairdressers graduating between 1985 and 2007 (n=5219) was performed. A questionnaire was sent in 2009 and 2020. The Danish Labor Marked Supplementary Pension Scheme provided information on affiliation to the hairdressing profession. Career length was assessed by Kaplan-Meier analyses. RESULTS: The median survival time was 12.0 (95% CI 11.0 to 13.0) years in graduates with OHE and 14.0 (95% CI 12.6 to 15.4) years in graduates without OHE (p<0.001). Graduates with a frequency of hand eczema (HE) of 'once', 'several times' and 'almost all the time' had a median survival time of 20.0 (95% CI 14.6 to 25.4), 12.0 (95% CI 10.7 to 13.3) and 7.0 (95% CI 5.6 to 8.4) years, respectively. Graduates with OHE that left the trade (partly) because of HE constituted 11.7% of the study population. Factors associated with leaving the trade because of HE included a history of atopic dermatitis (adjusted OR (aOR) 2.2 (95% CI 1.2 to 4.0), a history of a positive patch test (aOR 5.1 (95% CI 2.3 to 11.0) and allergy to hair dyes (aOR 9.4 (95% CI 3.4 to 25.6). CONCLUSION: Career length is reduced in hairdressers with OHE, especially if frequently relapsing or caused by contact allergy, for example, to hair dyes.

Epicutaneous Patch Testing in Type IV Allergy Diagnostics: State of the Art and Best Practice Recommendations.

This chapter summarises all relevant aspects of patch testing, closely following recommendations outlined in a recent European, and a German S3 guideline on diagnostic patch testing with contact allergens and medicinal products (drugs). Patch testing is indicated in patients suspected of suffering, or having been suffering, from delayed-type hypersensitivity leading to allergic contact dermatitis or other skin and mucosal diseases. Sections of this chapter include detailed indications, reasons for possibly postponing the test, considerations on choosing haptens (contact allergens) to test, various aspects of the application of patch test allergen preparations (storage, dosing) and of testing with individual materials provided by the patients. Special aspects of patch testing in cutaneous adverse drug reactions, children, or occupational contact dermatitis are outlined. Supplemental test methods, notably the repeated open application test, are briefly described. Finally, the final evaluation in terms of assessment of clinical relevance of reactions and patient counselling are outlined.

Respiratory toxicity of persulphate salts and their adverse effects on airways in hairdressers: a systematic review.

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.