according to a retrospective study of more than 30,000 patients.
Contact allergy to shoes remains a common but difficult problem for many reasons, including the limited information from shoe manufacturers, differences in shoe manufacturing processes, and changes in shoe trends, said Raina Bembry, MD, a dermatitis research fellow at Duke University, Durham, N.C., in a presentation at the annual meeting of the American Contact Dermatitis Society.
The North American Contact Dermatitis Group (NACDG) published data on shoe allergens from 2001-2004 in a 2007 review. To update this information to reflect changes in shoe manufacturing and trends, she and her coinvestigators characterized demographics, clinical characteristics, patch test results, and occupational data for NACDG patients with shoe contact allergy. They identified 33,661 patients who were patch tested with the standard series with or without a supplemental allergen between 2005 and 2018; over half were over aged 40.
The primary focus was individuals with a confirmed shoe (defined as shoes, boots, sandals, or slippers) as the source of a screening allergen or supplemental allergen, a positive patch test, and the foot as one of three sites of involvement. A total of 352 individuals met these criteria and had a confirmed final diagnosis of allergic contact dermatitis, Dr. Bembry said. Compared with individuals who had positive patch tests without a confirmed diagnosis, those with confirmed allergic dermatitis were significantly more likely to be male (odds ratio, 3.36) and less likely to be over aged 40 years (OR, 0.49).
The most common NACDG screening allergen, potassium dichromate, was found in 29.8% of the study population, followed by p-tert-butylphenol formaldehyde resin in 20.1%, thiuram mix (13.3%), mixed dialkyl thioureas (12.6%) and carba mix (12%).
Notably, 29.8% of the patients showed positive patch test reactions to supplemental allergens, and 12.2% only reacted to supplemental allergens, Dr. Bembry said.
The results were limited by several factors, including referral selection bias, reliance on clinical judgment for patch test interpretations, and lack of data on the specifics of the supplemental allergens other than the source code, she said. In addition, the study does not identify nonshoe sources of foot contact allergy, and six screening allergens were not testing during this study period.
Overall, the findings were similar to those from previous studies in that patients affected with contact dermatitis from shoe allergens tended to be younger and male, with no occupational relevance to the reaction, said Dr. Bembry.
The finding that almost 20% of allergens were not found with the screening series emphasizes the value of testing not only relevant supplemental allergens, but also patient products and shoe components, she concluded.
Dr. Bembry had no financial conflicts to disclose. Coauthor Amber Atwater, MD, the immediate past president of the ACDS, and associate professor of dermatology at Duke University, disclosed receiving the Pfizer Independent Grant for Learning & Change and consulting for Henkel.