Positive patch test reactions in older individuals: retrospective analysis from the North American Contact Dermatitis Group, 1994-2008.

BACKGROUND: Relatively little is known about the epidemiology of allergic contact dermatitis in older individuals. OBJECTIVES: We sought to determine the frequency of positive and clinically relevant patch test reactions in older individuals (≥ 65 years old) referred for patch testing, and to compare these results with those of adults (≤ 64-19 years) and children (<18 years). DESIGN: This was a retrospective cross-sectional analysis of North American Contact Dermatitis Group data from 1994 to 2008. RESULTS: A total of 31,942 patients (older n = 5306; adults n = 25,028; children n = 1608) were patch tested. The overall frequency of at least one allergic reaction in older individuals was 67.3% as compared with 66.9% for adults (P = .5938) and 47% for children (P = .0011). Reaction rates that were statistically higher in older individuals as compared with both adults and children included: Myroxylon pereirae, fragrance mix I, quaternium-15, formaldehyde, imidazolidinyl urea, diazolidinyl urea, neomycin, bacitracin, methyldibromo glutaronitrile, methyldibromo glutaronitrile/phenoxyethanol, ethyleneurea melamine formaldehyde mix, and carba mix (P values < .0004). Patch test reaction rates that were significantly lower in older individuals than both comparison groups included: nickel, thimerosal, and cobalt (P values < .0001). LIMITATIONS: Referral population was a limitation. CONCLUSIONS: Older individuals were more likely to have at least one positive patch test reaction as compared with children, but had similar rates to adults. The frequency of positive reactions to specific allergens differed by age group, most likely as a result of exposures.

Allergic patch test reactions associated with cosmetics: retrospective analysis of cross-sectional data from the North American Contact Dermatitis Group, 2001-2004.

BACKGROUND: Allergy to cosmetics is common. OBJECTIVES: We sought to characterize patients with positive patch test reactions associated with a cosmetic source, to identify common allergens; and to explore gender and occupational associations. METHODS: We performed a retrospective, cross-sectional analysis. RESULTS: Of 6621 female and 3440 male patients, 1582 female (23.8%) and 611 of male (17.8%) patients had at least one allergic patch test reaction associated with a cosmetic source. Of "allergic" patients (>1 allergic reaction, n = 6815), females were 1.21 times more likely to have an allergic reaction associated with a cosmetic source than were male patients (p < .0001, 95% confidence interval [CI] 1.12-1.31). Within the "cosmetic allergic" group (n = 2243), head and neck involvement was significantly higher in female than in male patients (49.3% vs 23.7%, p < .0001). One hundred twenty-five patients had occupationally related allergic reactions associated with a cosmetic. LIMITATIONS: This study is limited by its cross-sectional, retrospective design. CONCLUSION: Of all patients studied, 21.8% had an allergic reaction associated with a cosmetic. Site of dermatitis, cosmetic categories, and specific allergens differed somewhat by gender.

The value of patch testing patients with a scattered generalized distribution of dermatitis: retrospective cross-sectional analyses of North American Contact Dermatitis Group data, 2001 to 2004.

BACKGROUND: A scattered generalized distribution (SGD) of dermatitis is a challenging problem; patch testing is a strategy for evaluating allergic contact dermatitis as a relevant factor. OBJECTIVE: We sought to analyze patient characteristics and most frequently relevant positive allergens in patients presenting for patch testing with SGD. METHODS: We conducted retrospective cross-sectional analysis of North American Contact Dermatitis Group 2001 to 2004 data. Patients with SGD were compared with patients without SGD. RESULTS: Of 10,061 patients, 14.9% (n = 1497) had only a SGD. Men and patients with a history of atopic eczema were more likely to have dermatitis in a SGD (P < .001). Preservatives, fragrances, propylene glycol, cocamidopropyl betaine, ethyleneurea melamine formaldehyde, tixocortol pivalate, and budesonide were among the more frequently relevant positive allergens. Top allergen sources included cosmetics/beauty preparations/skin and health care products, clothing, and topical corticoids. LIMITATIONS: This was a retrospective analysis of patch-tested patients with SGD suspected to have allergy. CONCLUSIONS: A total of 49% of patients with SGD had at least one relevant positive allergen, thus demonstrating the benefit of patch testing these patients.

Complementary and alternative remedies: an additional source of potential systemic nickel exposure.

BACKGROUND: Systemic contact dermatitis from nickel has been reported from a number of sources including medical devices and following experimental oral exposure. OBJECTIVE: To identify other potential sources of systemic nickel exposure. METHODS: The internet and published medical literature were searched for complementary and alternative remedies which contain nickel. RESULTS: We identified and evaluated sources of nickel exposure in 4 homeopathic preparations, which are advertised to treat common skin diseases, as well as in a number of other homeopathic remedies, several herbal products and multivitamin mineral complexes. CONCLUSION: Complementary and alternative remedies are an additional source of systemic nickel exposure and at highest doses the potential risk for systemic contact dermatitis in nickel allergic patients should be considered.

Detection of nickel sensitivity has increased in North American patch-test patients.

BACKGROUND: Nickel allergy has been studied by contact dermatitis groups around the world, and the frequency of nickel sensitivity has been reported to be decreasing in some populations. OBJECTIVE: To review the prevalence of nickel allergy as observed by the North American Contact Dermatitis Group from 1992 to 2004. METHODS: The computer database of the North American Contact Dermatitis Group was used to examine the prevalence of nickel allergy over the study period and to analyze it by time, sex, and age. RESULTS: From 1992 to 2004, 25,626 patients were patch-tested. The percentage of women tested was fairly constant (61.4-66.3%). A steady increase in nickel sensitivity was seen from 1992 to 2004. Subgroup analysis did not identify a population with declining nickel allergy. CONCLUSIONS: Nickel allergy continues to increase in younger and older men and women patch-tested in North America.

Contact dermatitis of the hands: cross-sectional analyses of North American Contact Dermatitis Group Data, 1994-2004.

BACKGROUND: Hand dermatitis, including irritant and allergic contact dermatitis (ACD), is common. OBJECTIVE: To evaluate allergens, relevant irritants, sources and occupations associated with hand contact dermatitis using North American Contact Dermatitis Group (NACDG) data. METHODS: A cross-sectional analysis of 22,025 patients patch tested between 1994 and 2004. RESULTS: Hand involvement was found in 6953 patients; 959 had ACD as the only diagnosis. In these 959 patients, the 12 most frequent relevant allergens were quaternium-15 (16.5%), formaldehyde (13.0%), nickel sulfate (12.2%), fragrance mix (11.3%), thiuram mix (10.2%), balsam of Peru (9.6%), carba mix (7.8%), neomycin sulfate (7.7%), bacitracin (7.4%), methyldibromoglutaronitrile/phenoxyethanol 2.0% (7.4%), cobalt chloride (6.5%), and methyldibromoglutaronitrile/phenoxyethanol 2.5% (6.3%). Rubber allergens were most commonly associated with occupation. One third of patients with hand ACD had identifiable relevant irritants. LIMITATIONS: Cross-sectional analyses prevent evaluation of causal associations. CONCLUSION: In NACDG patients with hand ACD, the most common allergens included preservatives, metals, fragrances, topical antibiotics, and rubber additives.

Shoe allergens: retrospective analysis of cross-sectional data from the north american contact dermatitis group, 2001-2004.

BACKGROUND: Chemicals used in leather tanning, rubber processing, and/or adhesives are the most often-cited culprits in footwear dermatitis. Patch testing patients with suspected shoe dermatitis is essential for diagnosis and management. OBJECTIVES: The four goals for this study were to (1) determine the frequency of allergens associated with a shoe source in North American Contact Dermatitis Group (NACDG) patients with footwear allergic contact dermatitis; (2) compare these results to allergen frequencies from other published studies; (3) quantify the number of shoe-related reactions that were not identified with the NACDG standard series; and (4) identify relevant allergens not included on the NACDG standard series, based on data from other published studies. METHODS: The NACDG patch-tested 10,061 patients between 2001 and 2004. Data were retrospectively analyzed by (1) allergen source coded as "shoe," (2) site of dermatitis as "feet," and (3) diagnosis of "allergic contact dermatitis." RESULTS: Among the 109 NACDG patients with allergic contact dermatitis (ACD) of the foot and a shoe source of allergens, p-tertiary butylphenol formaldehyde resin, an adhesive, was the most common allergen, accounting for 24.7% of positive patch-test results, followed by potassium dichromate (17.5%) and carba mix (11.7%). When the data were examined according to groups of allergens, rubber chemicals (40.4%) were the most frequent allergens, followed by adhesives (32.5%), and leather components (20.1%). When data from published studies were pooled, potassium dichromate (31.5%) was the most frequent allergen, followed by p-tertiary butylphenol formaldehyde resin (17.1%) and cobalt chloride (12.9%). NACDG patients were statistically more likely to have positive patch-test reactions to p-tertiary butylphenol formaldehyde resin and statistically less likely to have a positive patch-test reaction to potassium dichromate than patients represented in pooled data from past studies. Nineteen (17.4%) of the 109 NACDG patients with ACD of the foot and a shoe source of allergens were identified as having a shoe source of a relevant allergen not included in the NACDG standard series. CONCLUSIONS: In NACDG patients, the most common individual shoe allergen was p-tertiary butylphenol formaldehyde resin. As a group, rubber chemicals were most common, a finding consistent with those of other studies.

Sensitivity of petrolatum and aqueous vehicles for detecting allergy to imidazolidinylurea, diazolidinylurea, and DMDM hydantoin: a retrospective analysis from the North American Contact Dermatitis Group.

OBJECTIVE: To determine whether petrolatum or aqueous vehicles are more sensitive for detecting allergy to imidazolidinylurea (IU), diazolidinylurea (DU), and dimethylol dimethyl hydantoin (DM). The relationship of these allergens to formaldehyde sensitivity was also explored. METHODS: Retrospective analysis of patients patch-tested by the North American Contact Dermatitis Group. All patients were simultaneously tested to seven allergens (formaldehyde, IU in petrolatum [pet], IU aqueous [aq], DU pet, DU aq, DM pet, and DM aq). Data were analyzed in pairs with various "gold standard" definitions of "true allergy" and adjusting for correlated data. RESULTS: Reaction to at least one of the seven allergens occurred in 2,398 patients. In all cases except one (which just approached statistical significance), the petrolatum-based allergen was statistically significantly more sensitive than the same allergen in an aqueous base. Most of the patients allergic to the three preservatives were also allergic to formaldehyde, but most formaldehyde-allergic patients were not allergic to the IU, DU, or DM. CONCLUSION: Of these two vehicles, petrolatum is significantly more sensitive than an aqueous vehicle is for detecting allergy to IU, DU, and DM.

Common contact allergens associated with eyelid dermatitis: data from the North American Contact Dermatitis Group 2003-2004 study period.

BACKGROUND: Allergic contact dermatitis can be manifest as an eruption confined to the eyelids. In regard to this specific presentation, only limited information on which to base the selection of patch tests for proper evaluation is available. OBJECTIVE: To identify the contact allergens most frequently found to be both patch test positive and relevant when only the eyelids are involved. METHODS: Data collected from 2003 to 2004 by the North American Contact Dermatitis Group (NACDG) were analyzed for relevant allergens in the setting of dermatitis on the eyelids only. Data on eyelid dermatitis patients whose relevant allergens were not among the 65 allergens used for screening during this study period were also tabulated. RESULTS: Data showed that 268 patients had only eyelid dermatitis and a final diagnosis of allergic contact dermatitis. In 193 (72%) of these, reactions were of current relevance and were identified from a screening series of 65 allergens. The top 26 allergens identified 65% of cases (175 cases). Gold was the most frequently encountered allergen (22 of 175 cases [12.5%]). Of the 268 cases, 33 showed relevant reactions to an allergen that was not among the 65 NACDG standard screening allergens. No specific allergen was identified in the remaining 42 cases. CONCLUSION: The top 26 allergens identified in this study represent a potential eyelid dermatitis screening series.

Improvement of cystic fibrosis during treatment with isotretinoin.

A 15-year-old boy with a history significant for multiple respiratory infections since birth presented for evaluation of acne vulgaris. He was initially prescribed doxycycline, topical tretinoin, and topical clindamycin solution, with the later addition of a benzoyl peroxide preparation to his regimen. The patient returned 6 months later after having been diagnosed with CF (cystic fibrosis) by sweat testing and genetic testing. His skin condition had not responded adequately to prior therapy, so all acne medications were discontinued. The 84-kg patient was started on 80 mg (0.95 mg/kg/d) of isotretinoin (13-cis-retinoic acid) daily. The patient's dose was decreased to 40 mg/d 2 weeks later following an episode of blood in his stool and epistaxis. At the 1- and 2-month follow-up visits, the patient reported improvement in his acne and mentioned that his lung secretions seemed reduced. His acne cleared after 4 months of therapy, so the isotretinoin was discontinued. The patient and his mother noted that no respiratory infections had occurred during the course of therapy. The patient's acne relapsed nearly 2 years later, so isotretinoin was restarted at 60 mg/d. During the next 7 months while on the drug, he experienced no further episodes of epistaxis or bloody stools and his acne had resolved by the end of therapy. The patient and his mother again reported fewer bronchopulmonary secretions and no infections requiring antibiotics during treatment with isotretinoin. This was unusual because he had experienced numerous respiratory infections requiring antibiotics during the prior 2 years. Since discontinuing the drug, the patient has had intermittent pulmonary infections and exacerbations in the symptomatology of his CF.

The Association of Race/Ethnicity and Patch Test Results: North American Contact Dermatitis Group, 1998-2006.

BACKGROUND: The North American Contact Dermatitis Group patch tests patients with suspected allergic contact dermatitis (ACD) to a broad series of screening allergens and publishes periodic reports. We have previously reported on the association of race and ethnicity with the rates of positive responses to standard patch test allergens. This report extends those observations. OBJECTIVE: The aim of the study was to report the North American Contact Dermatitis Group patch testing results from January 1, 1998, to December 31, 2006, comparing the frequency of positive reactions between white and black subjects. METHODS AND MATERIALS: Standardized patch testing with 45 allergens was used at 13 centers in North America. χ analysis of results in black subjects as compared with whites was examined. RESULTS: A total of 19,457 patients were tested; 92.9% (17,803) were white and 7.1% (1,360) were black. The final diagnoses of ACD (whites, 45.9%; blacks, 43.6%) and irritant contact dermatitis (13.0%/13.3%) were similar in the 2 groups. The diagnosis of atopic dermatitis was less common in the white patients (8.9%) as compared with the black patients (13.3%). Positive patch test reactions rates were similar for most allergens. However, statistically, blacks reacted more frequently to p-phenylenediamine (7.0% vs 4.4%, P < 0.001), bacitracin (11.6% vs 8.3%, P = 0.0004), as well as specific rubber accelerators mercaptobenzothiazole (2.7% vs 1.8%), thiuram (6.2% vs 4.3%), and mercapto mix (1.9% vs 0.8%, P < 0.001). Whites had an increase in positive reactions to fragrances (12.12% vs 6.77%, P < 0.0001), formaldehyde (9.25% vs 5.45%, P < 0.0001), and some formaldehyde releaser preservatives used in personal care products and textile resins (9.80% vs 6.18%, P < 0.0001). CONCLUSIONS: There were statistically different rates of positive patch test reactions to specific allergens between black and white patients suspected of having ACD. The etiology of these differences is unclear but probably relates to culturally determined exposure patterns rather than genetic differences.

North American Contact Dermatitis Group patch-test results, 2001-2002 study period.

BACKGROUND: Allergic contact dermatitis is a significant cause of cutaneous disease affecting many individuals in the home and at the workplace. Patch testing is the most worthwhile diagnostic tool for the evaluation of patients with suspected allergic contact dermatitis. OBJECTIVE: This study reports the results of patch testing from January 1, 2001, to December 31, 2002, by the North American Contact Dermatitis Group (NACDG). METHODS: Patients were tested with an extended screening series of 65 allergens. A standardized patch-testing technique was used. Data from these patients were recorded on a standardized computer entry form and analyzed. RESULTS: Sixty-five allergens were tested on 4,913 patients. The top 10 allergens remain the same in this study period as in the 1999-2000 study period: nickel sulfate (16.7%), neomycin (11.6%), Myroxilon pereirae (balsam of Peru) (11.6%), fragrance mix (10.4%), thimerosal (10.2%), sodium gold thiosulfate (10.2%), quaternium-15 (9.3%), formaldehyde (8.4%), bacitracin (7.9%), and cobalt chloride (7.4%). Of the 4,913 patients tested, 69% had at least one positive allergic patch-test reaction. Of all patients, 15.8% had occupation-related dermatitis; 15.4% were determined to have irritant contact dermatitis, and 11.1% of the 15.4% had a relevant reaction to an occupational irritant. Of all patients tested, 16.7% had a relevant reaction to an allergen not in the NACDG standard series, and 5.5% had a relevant reaction to an occupational allergen not in the standard series. CONCLUSION: Our findings once again reinforce the need for a more comprehensive group of diagnostic allergens than those found in the standard screening kits. The usefulness of patch testing is enhanced when a greater number of allergens are tested, especially nonstandard allergens occupationally encountered.

Allergy to cocamidopropyl betaine and amidoamine in North America.

BACKGROUND: The prevalence of allergy to cocamidopropyl betaine (CAPB) in North America has not been previously reported. OBJECTIVE: The aim of this study was to report on the most recent data on allergy to CAPB and a related allergen, amidoamine (AA). METHODS: Data was collected by the North American Contact Dermatitis Group from consecutive patients presenting for patch testing for diagnosis of presumed allergic contact dermatitis (ACD) from January 1, 2001, through December 31, 2001. RESULTS: Of 975 patients tested, 15 were patch-test positive to CAPB, 25 had positive reactions to AA, and 18 had positive reactions to both CAPB and AA. The most frequent site of dermatitis from CAPB was the head and neck region. CONCLUSION: In North America, both CAPB and AA are useful allergens for detecting ACD.

North American Contact Dermatitis Group patch test results for 2007-2008.

BACKGROUND: The North American Contact Dermatitis Group (NACDG) tests patients with suspected allergic contact dermatitis to a broad series of screening allergens and publishes periodic reports. OBJECTIVE: The aims of this study were to report the NACDG patch-testing results from January 1, 2007, to December 31, 2008, and to compare results to pooled test data from the previous 2 and 10 years to analyze trends in allergen sensitivity. METHODS AND MATERIALS: Standardized patch testing with 65 allergens was used at 13 centers in North America. χ analysis was used for comparisons. RESULTS: A total of 5085 patients were tested; 11.8% (598) had an occupationally related skin condition, and 65.3% (3319) had at least 1 allergic patch test reaction, which is identical to the NACDG data from 2005 to 2006. The top 15 most frequently positive allergens were nickel sulfate (19.5%), Myroxylon pereirae (11.0%), neomycin (10.1%), fragrance mix I (9.4%), quaternium-15 (8.6%), cobalt chloride (8.4%), bacitracin (7.9%), formaldehyde (7.7%), methyldibromoglutaronitrile/phenoxyethanol (5.5%), p-phenylenediamine (5.3%), propolis (4.9%), carba mix (4.5%), potassium dichromate (4.1%), fragrance mix II (3.6%), and methylchloroisothiazolinone/methylisothiazolinone (3.6%). There were significant increases in positivity rates to nickel, methylchloroisothiazolinone/methylisothiazolinone, and benzophenone-3. During the same period of study, there were significant decreases in positivity rates to neomycin, fragrance mix I, formaldehyde, thiuram mix, cinnamic aldehyde, propylene glycol, epoxy resin, diazolidinyl urea, amidoamine, ethylenediamine, benzocaine, p-tert-butylphenol formaldehyde resin, dimethylol dimethyl hydantoin, cocamidopropyl betaine, glutaraldehyde, mercaptobenzothiazole, tosylamide formaldehyde resin, budesonide, disperse blue 106, mercapto mix, and chloroxylenol. Twenty-four percent (1221) had a relevant positive reaction to a non-NACDG supplementary allergen; and 180 of these reactions were occupationally relevant. CONCLUSIONS: Periodic analysis, surveillance, and publication of multicenter study data sets document trends in allergen reactivity incidence assessed in the patch test clinic setting and provide information on new allergens of relevance.

Occupational contact dermatitis in hairdressers/cosmetologists: retrospective analysis of north american contact dermatitis group data, 1994 to 2010.

BACKGROUND: European studies document that occupational contact dermatitis (CD) is common in hairdressers, but studies from North America are lacking. OBJECTIVES: The objectives of this study were to estimate the prevalence of occupational CD among North American hairdressers/cosmetologists (HD/CS) and to characterize responsible allergens and irritants as well as their sources. METHODS: A cross-sectional analysis of patients patch tested by the North American Contact Dermatitis Group between 1994 and 2010 was conducted. RESULTS: Of 35,842 patients, 432 (1.2%) were HD/CS. Significantly, most of the HD/CS were female (89.8%) and younger than 40 years (55.6%) as compared with non-hairdressers (P < 0.0001). The rates for allergic and irritant CD in HD/CS were 72.7% and 37.0%, respectively. The most common body site of involvement was the hand, and this was significantly more common than in non-HD/CS (P < 0.0001). The most frequent currently relevant and occupationally related allergens were glyceryl thioglycolate, p-phenylenediamine, nickel sulfate, 2-hydroxyethyl methacrylate, and quaternium-15. Hair dyes, permanent wave solutions, and other hair products were common sources of allergens. The North American Contact Dermatitis Group allergen series missed at least 1 occupationally-related allergen in 26.2% of patients. CONCLUSIONS: Contact dermatitis in North American HD/CS is common, and occupationally related allergens are those found in HD/CS products. Supplemental hairdressing/cosmetology antigen series are important in detecting all occupationally related allergens in this population.

Positivity ratio and reaction index: patch-test quality-control metrics applied to the north american contact dermatitis group database.

BACKGROUND: The positivity ratio (PR) and reaction index (RI) characterize the ability of patch-test preparations to produce strong (++ or +++) reactions as opposed to weak (+), questionable, or irritant reactions. OBJECTIVE: This study evaluates these measures for North American Contact Dermatitis Group (NACDG) patch-test preparations. METHODS: The PR and RI were calculated for 79 NACDG standard allergens tested from 1994 to 2006 (n = 26,479 patients). The median values were used as cutoff values for "acceptable" versus "problematic" preparations. RESULTS: The top 10 "acceptable" patch-test preparations (PR < or = 55 and RI > 0.46) were mixed dialkyl thioureas 1% in petrolatum (pet), tixocortol-21-pivalate 1% pet, ethylenediamine dihydrochloride 1% pet, sesquiterpene lactone mix 0.1% pet, nickel sulfate 2.5% pet, bacitracin 20% pet, thimerosal 0.1% pet, epoxy resin 1% pet, colophony 20% pet, and mercaptobenzothiazole 1% pet. The most "problematic" patch-test preparations (PR > 55 and RI < or = 0.46) were cocamidopropyl betaine 1% aqueous (aq), benzalkonium chloride 0.1% aq, jasmine absolute 2% pet, iodopropynyl butyl carbamate 0.1% pet, 2-bromo-2-nitropropane-1,3-diol 0.5% pet, methyldibromoglutaronitrile 0.4% pet, methyldibromoglutaronitrile/phenoxyethanol 2% pet and 2.5% pet, dimethylol dihydroxyethyleneurea 4.5% aq, and clobetasol-17-propionate 1% pet. CONCLUSION: Caution should be used when interpreting reactions to "problematic" patch-test preparations with a high proportion of weak, irritant, and questionable reactions.

Positive patch-test reactions to iodopropynyl butylcarbamate: retrospective analysis of North American contact dermatitis group data, from 1998 to 2008.

BACKGROUND: iodopropynyl butylcarbamate (IPBC), a commonly used preservative, is found in industrial and personal care products. OBJECTIVE: to evaluate prevalence, clinical relevance, occupational relationship, and sources of positive reactions to IPBC in patients in North America. METHODS: the North American Contact Dermatitis Group (NACDG) tested IPBC 0.1% and/or 0.5% in petrolatum (pet) between 1998 and 2008. Two patient groups of interest were defined, based on patch-test reactions to IPBC: weak (+) reactors and strong (++ or +++) reactors. Patient characteristics, site(s) of dermatitis, sources of positive reactions, clinical relevance, and occupational relevance to IPBC were tabulated. RESULTS: of the 25,321 patients tested, there were 226 (0.9%) weak reactors and 67 (0.3%) strong reactors. For IPBC-positive patients, the most frequent sites of dermatitis were scattered generalized distribution, hands, and arms. The majority (> 50%) of currently relevant reactions were to personal care products, and most reactions (> 90%) were not related to occupation. Only four of the strong reactors had definite clinical relevance (positive use-test reaction or positive patch-test reaction to a product containing IPBC). The frequency of positive reactions increased (0.2% vs 1.5%) when the higher concentration of IPBC was utilized, but most (> 64%) were weak reactions, of which some were likely irritant. CONCLUSIONS: allergy to IPBC is relatively uncommon. When clinically relevant, personal care products were the most likely allergen source. Because IPBC is a marginal irritant, caution should be utilized when testing with higher concentrations of IPBC (≥ 0.5% pet) and when interpreting weak (+) reactions. Verification of clinical relevance by use test or repeat patch testing or both is also important.