Immune response to topical sodium lauryl sulfate differs from classical irritant and allergic contact dermatitis.

Sodium lauryl sulfate (SLS) is used as a control irritant in patch testing for allergic contact dermatitis (ACD). However, up to 20% of those tested react to SLS, whereby the pathophysiological basis of this reaction is still unclear. To mimic patch test reactions, we repeatedly applied SLS to the skin of wild-type mice. Reactions were compared with those in a classical ACD model induced by oxazolone and an irritant contact dermatitis (ICD) model induced by croton oil. Skin inflammation was assessed with ear thickness measurements, immunohistochemistry, qRT-PCR, and flow cytometry. Topical SLS treatment was further investigated in Flg/Hrnr-/-, Myd88/Tlr3-/-, and Rag1-/- mouse models. All three compounds caused ear swelling with different courses. Oxazolone treatment, compared with the ICD model, resulted in a greater influx of immune cells (CD4+, MHCII+, CD11b+). Similarly, SLS did not induce immune cell infiltration or expression of selected inflammatory and regulatory cytokines. SLS induced the most pronounced keratinocyte proliferation. Compared with wild-type mice, topical SLS application did not increase ear swelling in skin barrier deficient Flg/Hrnr-/- mice, but led to significantly delayed swelling in mice with defects in innate or adaptive immune functions (Myd88/Tlr3-/-, Rag1-/-). SLS-induced contact dermatitis differed from classical ACD and ICD, as it elicited less pronounced immune alterations. Skin barrier impairment does not affect SLS-induced contact dermatitis, whereas both innate and adaptive components are involved in SLS skin reactions.

Influence of Surfactant on the Skin Permeation of Methylisothiazolinone and Methylchloroisothiazolinone.

Patch tests are often used in safety evaluations to identify the substance causing skin irritation, but the same substance can sometimes give positive or negative results depending on the test conditions. Here, we investigated differences in the skin penetration of two test compounds under different application conditions. We studied the effects of the anionic surfactant sodium dodecyl sulfate (SDS) and the nonionic surfactant polysorbate 80 (PS) on skin penetration of the preservatives methylisothiazolinone (MT) and methylchloroisothiazolinone (MCT), which are used in cosmetics such as shampoos. The skin permeation of MT was enhanced by SDS but was unchanged by PS. Skin impedance decreased in the presence of SDS whereas PS had the same effect as the control aqueous solution, suggesting that SDS reduction of the barrier function of skin affects the permeation of MT, a hydrophilic drug. Application of a mixture of MCT and MT in the presence of SDS did not affect the skin permeation of MCT whereas the permeation of MT was enhanced by SDS, indicating that the skin permeation of MCT is less affected by SDS than is MT. Thus, attention should be paid to the possible effect of co-solutes, especially hydrophilic drugs.

IgE to wheat, prick test, and Patch test among children with celiac disease.

INTRODUCTION AND AIM: Celiac disease is one of the most common autoimmune disorders. This study aimed to evaluate the relationship between celiac disease and wheat sensitization. SUBJECTS AND METHODS: In the current study, children aged < 18 years with confirmed celiac disease were included. Data were analyzed using SPSS. RESULTS: Gastrointestinal problems were the most common indication for evaluation in terms of celiac disease. Prick and patch tests were positive in 43.4% and 34% respectively. CONCLUSION: Prick test and patch test for wheat sensitization were positive in about 30-45% of the children for celiac disease.

Allergic contact dermatitis due to 1,6-hexanediol diacrylate in ostomy patients.

BACKGROUND: Many people live with ostomies after life-saving surgery. Ostomy patients often suffer from peristomal dermatitis. Allergic contact dermatitis (ACD) has been reported, mostly due to contact allergy (CA) to topical agents. OBJECTIVES: We present three patients with therapy resistant peristomal dermatitis, suggesting ACD caused by different stoma products. METHODS: Patch testing was performed with baseline series, additional series, and selected allergens. They were also tested with their own ostomy products as is and separate extracts of the products. Extracts were analysed using Gas Chromatography-Mass Spectrometry (GC-MS). RESULTS: In all three patients we diagnosed CA to 1,6-hexanediol diacrylate (HDDA), +++ in case (C) 1 and 3, ++ in C 2. HDDA was detected in C 2's ostomy pouch adhesive and in C 1's and 3's flange extenders used to improve the adhesion of the ostomy pouches. CONCLUSION: Therapy resistant peristomal dermatitis should always be suspected of ACD and patch testing, especially with the patient's own products, should be performed.

Outbreak of contact allergy to dicyclohexylcarbodiimide in a biotechnology laboratory.

BACKGROUND: Dicyclohexylcarbodiimide (DCC) is known to cause occupational allergic contact dermatitis in biotechnology laboratory workers. OBJECTIVES: This study aimed to assess the prevalence of DCC sensitization among workers of one biosynthesis laboratory and to determine the optimal DCC concentration for patch testing. MATERIALS AND METHODS: 23 laboratory workers frequently exposed to DCC of whom 21 suffered from dermatitis and 11 controls were enrolled into the study. All participants underwent skin patch testing with different concentrations of DCC and other substances used in the work environment. Statistical analysis was conducted to compare results between active and control groups. RESULTS: Of the 23 workers tested, 56.5% showed positive reactions to DCC. All of them had dermatitis. Morpholine also elicited positive reactions in 26.1% of workers who were all sensitized to DCC. Dimethylformamide and chloroform yielded negative results. CONCLUSION: Dicyclohexylcarbodiimide was a major cause of contact dermatitis in the active group indicating an outbreak of contact allergy to DCC in the company necessitating preventive measures. Both DCC 0.1% ac. and DCC 0.05% pet. should both be used for patch testing.

Increased rates of contact allergy to selected preservatives in patients with allergic contact dermatitis in Turkey.

BACKGROUND: Preservatives are a frequent cause of allergic contact dermatitis (ACD) and have caused numerous epidemics. OBJECTIVES: The objective of this study is to determine the prevalence of preservative sensitivity, assess the change in the frequency of sensitivity, identify new preservatives with increased sensitivity rates, and evaluate the situation in Turkey by comparing our findings with current literature. METHODS: A total of 201 patients diagnosed with ACD between 2018 and 2020, were patch tested with the European baseline series and additional seven preservative haptens. The change in the prevalence of sensitivity to each preservative hapten was investigated by comparing the data from the study conducted in our department between 2000 and 2004. RESULTS: Results showed that 17.4% (n = 35) of the patients were positive to preservatives. Comparison with previous data from 2000 to 2004 revealed an increase in the frequency of sensitization. The most prevalent allergen was methyldibromo glutaronitrile (9.5%), followed by methylchloroisothiazolinone/methylisothiazolinone (6.5%), and methylisothiazolinone (5%). CONCLUSION: The increase in preservative sensitivity in Turkey is the most remarkable finding. Although MDBGN was prohibited in cosmetic products, MCI/MI and MI are still widely used. Our findings suggest that awareness of preservative sensitivity should be increased and additional precautions should be taken, also in Turkey, regarding the use of preservatives.

Contact allergens in African countries: A review of published patch test studies.

Only few studies on contact allergy in African countries have been published. The aim of the present study was to provide an overview of the most common contact allergens identified by the use of patch tests in African countries based on a review of the existing literature. A total of twenty-four publications from eight African countries were initially identified by search in PubMed. The abstracts and method sections were screened, and 15 studies in which patch tests were actually used to identify the allergen causing the allergic contact dermatitis (ACD) were finally selected. Nickel, cobalt, chromium, fragrance mix and p-tert-butylphenol-formaldehyde resin were the dominating contact allergens responsible for 40%-90% of the positive patch test reactions. This study indicates that a targeted effort directed towards prevention, avoidance and regulation of reliably identified contact allergens could reduce the disease burden of ACD considerable in some African countries.

Sensitisation to ethylhexyl salicylate: Another piece of the frontal fibrosing alopecia puzzle.

BACKGROUND: There is speculation that some environmental factors may be impacting the increasing incidence of frontal fibrosing alopecia (FFA). In a recent publication, sensitisation to benzyl salicylate was shown to be prevalent among 36 patients with FFA. Ethylhexyl salicylate (EHS), a light stabiliser, ultraviolet (UV) B absorber and UV filter, frequently found in photoprotectors/cosmetics and, rarely reported as a sensitiser, was not patch tested in said research. METHODS: From January 2021 to February 2022, 33 patients with FFA were patch-tested with the European Photopatch Series, including EHS 10% pet. in two hospitals. In addition, we conducted a literature review and a market survey. RESULTS: Patch test reactions to EHS were identified in 9 of 33 (27.3%). Four of nine also reacted to their personal sunscreens (containing EHS). All involved women with a mean age of 54 (30-65). Five patients had been diagnosed with FFA before the patch tests; and, four were diagnosed with FFA during the patch test investigations. CONCLUSION: Sensitisation to EHS was frequently found in a selected population of patients with FFA. We propose to expand the spectrum of contact allergens described in patients with FFA to include EHS and discuss the possible need for optimization of the patch test preparation.

Contact allergy in atopic dermatitis: A prospective study on prevalence, incriminated allergens and clinical insights.

BACKGROUND: The relationship between atopic dermatitis (AD) and allergic contact dermatitis (ACD) is a matter of debate. OBJECTIVES: The purpose of our study is to assess the frequency of ACD in patients with AD, the incriminated allergens and the potential risk factors. METHODS: This is a prospective study, including cases of AD diagnosed based on Hanifin and Rajka's criteria. All patients were patch tested to the European baseline series and corticosteroid series. RESULTS: Ninety-three patients were included. Fifty-six patients (60.2%) had positive patch test results of which 71.4% were relevant. The most frequent allergens were: textile dye mix (24.7%), nickel (20.4%), cobalt (12.9%), isothiazolinone (8.6%), quanterium 15 (4.3%) and balsam of Peru (4.3%). Chromium, fragrance mix I, fragrance mix II and PTBP were positive in three cases (3.2%). Two cases of allergy to corticoids were identified. Facial involvement and duration of AD were significantly associated with contact sensitization (p = 0.04 and p = 0.005, respectively). Avoidance of relevant allergens resulted in a statistically significant decrease in SCORAD (p < 0.001). CONCLUSIONS: ACD remains an important co-morbidity of AD. We observed a high frequency of ACD to textile dyes, isothiazolinones and fragrances. Avoidance of relevant allergens has resulted in an improvement of patients' skin symptoms.

Comparison of patch testing Brazilian (Green) propolis and Chinese (poplar-type) propolis: Clinical epidemiological study using data from the Information Network of Departments of Dermatology (IVDK).

BACKGROUND: Propolis types differ regarding their chemical composition. OBJECTIVES: To compare patch test results based on Brazilian (Green) propolis with data based on Chinese (poplar-type) propolis, and to evaluate the specifications of raw materials used for the PT preparations. METHODS: In the Information Network of Departments of Dermatology (IVDK), 1290 consecutive patients were patch tested with Brazilian (Green) propolis (NH400, SmartPractice Europe). Patch test reactivity was compared with results obtained with Chinese (poplar-type) propolis (NA71, SmartPractice Europe) by calculating frequencies and corresponding 95% confidence intervals. Data on the specifications of raw materials used for NH400 and NA71 were obtained from the manufacturer. RESULTS: Positive reactions to NH400 were found in 303 (23.5%) patients with unclear clinical relevance in most cases. Patients reacting to NH400 were less often sensitised to fragrances and colophony, but more often to nickel sulphate and cobalt chloride than patients reacting to NA71. The NH400 batch used contained high levels of aerobic bacteria, and was not purified by ethanolic extraction. CONCLUSIONS: Pattern of concomitant reactivity along with raw material properties suggests that the high frequency of positive reactions to NH400 may primarily result from bacterial contamination or impurities in the PT preparation rather than from propolis constituents.

Allergic contact dermatitis to salicylic acid: A case series of relevant sensitization.

INTRODUCTION: Allergic contact dermatitis (ACD) to salicylic acid (SA) is widely unreported. Furthermore, cross-reactivity between SA and other salicylates has not been reported despite well-documented in-group salicylate cross-reactivity. OBJECTIVE: To describe our clinic's experience patch testing to SA, highlighting seven cases of relevant reactions and concomitant reactivity with other salicylates. METHODS: Results of patch testing to 5% SA in petrolatum between 1 January 2020, and 9 February 2024, are reported. Seven cases of relevant reactions to SA are detailed. RESULTS: A total of 489 patients (27.5%) were tested to SA, 21 of which were positive: 7 doubtful (+/-), 14 weak positive (+), and no strong/extreme positive reactions. Four irritant reactions were documented. Of the 14 weak positive (+) reactions, 7 had definite or probable clinical relevance, 5 of which also reacted to other salicylates. CONCLUSIONS: ACD to SA is likely underreported due to a lack of testing. In our experience, testing SA 5% petrolatum is tolerable without significant irritation. Cross-reactivity between SA and other salicylates is probable. Though SA appears to be the primary sensitizer in some cases, more studies are needed to understand its possible role as a marker for salicylate allergy.

Contact allergy to SIDAPA baseline series allergens in patients with eyelid dermatitis: An Italian multicentre study.

BACKGROUND: Eyelid dermatitis is a frequent reason of dermatological consultation. Its aetiology is not univocal, being contact dermatitis, both allergic and irritant, the most frequent. The primary sources of allergen exposure include cosmetics, metals, and topical medications, from direct, indirect, or airborne contact. OBJECTIVES: To define the frequency of positive patch test reactions to SIDAPA baseline series allergens, to document positive allergens, and to precise the final diagnosis in patients with eyelid involvement. METHODS: A total of 8557 consecutive patients from 12 Italian Dermatology Clinics underwent patch testing with SIDAPA baseline series in 2018 and 2019. Patients were divided into two groups: (i) with eyelid involvement with or without other involved sites (E-Group) and (ii) without eyelid involvement (NE-Group). The final diagnosis and the frequency of positive relevant patch test reactions were evaluated. RESULTS: E-Group consisted of 688 patients (females 78.6%, mean age 45.3 years), 8.0% of 8557 consecutively patch-tested patients. The final diagnosis in E-Group was ADC in 42.4%, ICD in 34.2%, and AD in 30.5%. The highest reaction rates were elicited by nickel sulphate and methylchloroisothiazolinone/methylisothiazolinone in both E-Group and NE-Group, even if these allergens were significantly more frequently positive in NE-Group patients than in E-Group ones. Positive patch test reactions to fragrance Mix II, dimethylaminopropylamine, and sorbitan sesquiolate were significantly more frequent in E-Group patients than in NE-Group ones. CONCLUSIONS: Eyelid dermatitis is a frequent dermatological complaint. Allergic contact dermatitis is the most frequent diagnosis commonly caused by nickel sulphate, isothiazolinones, and fragrances. The surfactants dimethylaminopropylamine and sorbitan sesquioleate are emerging causes of eyelid allergic contact dermatitis.

Contact sensitization and self-reported eczema in Swedish painters with occupational exposure to isothiazolinones.

BACKGROUND: Due to an increasing occupational usage of isothiazolinone (IT)-containing preservatives, and their potential to cause skin sensitization and allergic contact dermatitis, that is, chronic disease, there is a need for more knowledge on how highly exposed workers are affected. OBJECTIVES: The overall objective was to explore dermatological symptoms of potentially long-lasting or chronic character in Swedish painters. METHODS: Building painters from western and southern Sweden were initially invited to perform a questionnaire on occurrence of skin symptoms. Participants with affirmative responses, and the right inclusion criteria, were further invited to patch testing with four different ITs: benzisothiazolinone (BIT), methylisothiazolinone, methylchloroisothiazolinone and octylisothiazolinone. RESULTS: There was a tendency towards higher occurrence of positive patch test reactions among the painters compared with occupationally unexposed registry patients; however, not statistically significant differences. BIT was the substance most frequently causing positive test results in both groups. The occurrence of adult-onset eczema was higher in painters than in the control group of electricians, and just shy of statistical significance concerning any of several skin locations (face/legs/arms/hands). CONCLUSION: Building painters present with positive patch test reactions to common paint preservatives (ITs), and they report adult-onset eczema more often than do less occupationally exposed groups.

Patch test results to the Spanish baseline patch test series according to age groups: A multicentric prospective study from 2019 to 2023.

INTRODUCTION: Patch test results may be influenced by age-related factors. However, there is still discordant evidence between age and patch test results. OBJECTIVES: We aim to evaluate the patch test results reflecting skin sensitisation, their relevance and association with clinical features by age group. METHODS: Prospective multicentric study of all patients patch tested with the Spanish baseline series in participating centres. Age groups were pre-defined as children (0- to 11-years), adolescents (12- to 18-years), young adults (19- to 30-years), middle-aged adults (31- to 65-years) and older adults (≥66-years). Occurrence of sensitisation, relevance and clinical features were compared by age group. Factors associated with skin sensitisation were investigated with multivariate logistic regression. RESULTS: A total of 13 368 patients were patch-tested. Differences in positive patch test results and relevance by age were detected with the highest proportion in middle-aged adults. Age-related trend differences were found for nickel, potassium dichromate, caines, colophony, Myroxylon pereirae resin, 2-hydroxyethyl methacrylate and limonene hydroperoxide. The multivariate logistic analysis (adjusted for sex, atopic dermatitis, body location and occupational dermatitis) showed an association between the age group of 31-65 (OR: 1.41, 95% CI: 1.26-1.58) and above 66-years (OR: 1.15, 95% CI: 1.01-1.32) with a higher proportion of positive results, compared with young adults. CONCLUSIONS: Positive patch test results vary according to age, with the highest occurrence in middle-aged adults. Most haptens did not present age-related differences, reinforcing the use of baseline series regardless of age.

Allergic contact dermatitis to footwear in Thailand: Prevalence, clinical characteristics and common allergens.

BACKGROUND: Footwear contact allergy is caused by exposure to allergens in shoes. The prevalence and common allergens vary by region and time due to differences in customs and lifestyle. OBJECTIVES: To determine the clinical characteristics and common allergens of patients with footwear-related allergic contact dermatitis (ACD) who attended Siriraj Hospital in Bangkok, Thailand, between 2001 and 2020. METHODS: The medical records of 247 patients with clinically suspected footwear dermatitis who underwent patch testing were reviewed. RESULTS: The prevalence of ACD to footwear was 1.8%. Females were predominant (71.6%). The three most common allergens were carba mix (7.7%), mercapto mix (6.9%) and potassium dichromate (6.9%). According to the allergens found, rubber (14.2%), adhesives (7.7%) and leathers (6.9%) were the three most common groups. Dorsal-limited skin lesions were significantly associated with footwear ACD. CONCLUSION: Rubber and leather allergens were still the most common culprit allergens. Dermatologists should keep up-to-date on common allergens in footwear and emerging allergens to include in patch test series.

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.

Patterns of simultaneous contact allergies in patients with contact sensitization to oxidised linalool and oxidised limonene.

BACKGROUND: Contact allergy rates of linalool and limonene hydroperoxides (HPs) have increased. OBJECTIVES: To demonstrate the patterns of simultaneous positive patch test (PT) reactions and prevalences of multiple contact allergies (MCAs) in patients with contact allergy to linalool and/or limonene HPs. METHODS: A retrospective analysis of consecutive dermatitis patients in 2015-2020 was performed. RESULTS: Of all 4192 patients, 1851 had at least one positive PT reaction. Of these, 410 (22.2%) had MCAs, significantly related to a higher age (p-value = 0.003). Patients with an exclusively positive reaction to linalool HPs but not limonene HPs were shown to have MCAs (p-value <0.001, odds ratio (95% confidence interval) = 4.15 (3.01-5.73)). Patients with simultaneous contact allergies to both linalool and limonene HPs had contact allergies to many other screening and fragrance allergens. CONCLUSIONS: Simultaneous positive PT reactions to allergens in baseline series and fragrances are common in patients with the HPs contact allergy, especially linalool HPs. The pattern of simultaneous PT reactions principally suggested the co-sensitization of the cosmetic allergens.

Allergic contact dermatitis in adults with and without atopic dermatitis: Evaluation of the Spanish Contact Dermatitis Registry (REIDAC).

BACKGROUND: Atopic dermatitis (AD) and allergic contact dermatitis (ACD) are inflammatory skin conditions whose association is not clearly defined. OBJECTIVES: To identify differences in ACD profile between patients with and without AD among those referred for patch testing. Additionally, to determine the prevalence of sensitisation to standard Spanish contact allergens in both groups. METHODS: We analysed two groups (AD and non-AD) within the Spanish Registry of Research in Contact Dermatitis and Cutaneous Allergy (REIDAC). Contact allergy, clinical relevance and epidemiological data were compared between them. RESULTS: A total of 5055 patients were included. Among them, 23% (1168) had a history or final diagnosis of AD. At least one positive reaction was seen in 468 (40%) of AD patients and 1864 (48%) of non-AD patients. In both groups, the most common positive reactions were to nickel sulphate, methylchloroisothiazolinone/methylisothiazolinone and cobalt chloride. Age-adjusted OR for sensitisation to nickel sulphate was 0.72 (95% CI: 0.61-0.86), indicating a decreased likelihood of sensitisation in AD patients compared to non-AD individuals. CONCLUSIONS: We did not find an increased presence of ACD in patients with AD referred for patch testing, exhibiting similar profiles to non-AD population, except for a negative relationship between AD and sensitisation to nickel sulphate.

Prevalence of contact allergy to gold in dermatitis patients from 2010 to 2024: A systematic review and meta-analysis.

Gold contact allergy is diagnosed by patch testing using gold chloride or gold sodium thiosulfate. These tests often show high positivity rates, but a direct correlation with dermatitis from everyday gold exposure is rare. The aim of this study was to investigate and estimate the current prevalence of gold contact allergy in dermatitis patients. We performed a systematic literature search in PubMed, Embase and Web of Science for studies reporting the prevalence of gold contact allergy in dermatitis patients and published between January 2010 and May 2024. Data extraction and quality assessment were performed, and pooled proportions were calculated using random effects models. Sixteen studies with 14 887 dermatitis patients were included. The pooled prevalence of gold contact allergy was 14.1% (95% confidence intervals: 9.5%-19.4%) with significant heterogeneity (I2 = 98.3%). High positivity rates with limited clinical relevance highlight the need for cautious interpretation. Even within the same country, studies find different prevalence rates. Standardized testing protocols and further research are needed to better understand and manage this allergy.

Comparison of patch test positivity after 24 and 48 hours of occlusion time in patients of allergic contact dermatitis: A prospective study.

BACKGROUND: Patch test is the gold standard for diagnosing allergic contact dermatitis. Conventionally, the patches are applied for 48 h, which in tropical weather conditions causes excessive sweating, leading to irritation, and sometimes the patches come off, making the test inconclusive. OBJECTIVE: To compare the patch test positivity after 24 and 48 h of occlusion time in patients of allergic contact dermatitis, using standard allergen concentration. MATERIALS AND METHODS: Clinically suspected patients of allergic contact dermatitis were enrolled and patch tested using the Indian Standard Series, parthenium acetone extracts (1:50, 1:100 and 1:200 dilutions) and patient material. Patches were applied in duplicate on either side of the back, using a random number table. One set of patches was removed after 24-h of occlusion, while the other set after 48-h. Readings were performed at 48- and 96-h by two independent dermatologists, blinded to the duration of occlusion. RESULTS: The study had 97 adult patients (58 males and 39 females; mean age: 48.12 ± 13.07 years). A total of 133 and 142 positive reactions were observed after 48 h occlusion at 48 and 96 h reading, respectively. Of these 117 (87.9%) and 132 (92.9%) patches were positive and concordant and noted at 24 h occlusion time. The Cohen's kappa coefficient were 0.94 for 48 h and 0.97 for 96 h reading, hence showing an almost complete agreement (ⱪ > 0.81) between patches occluded for 24 and 48 h. CONCLUSION: Though there is no significant difference in patch test positivity among ISS allergens after either occlusion time, 48 h occlusion performs significantly better compared with 24 h, when reactions of all allergens (ISS, patient material and parthenium acetone extract) are analysed together.