When the Allergen Is Not What You Expected: 2 Contact Dermatitis Cases

Correctly attributing a contact dermatitis diagnosis often requires looking past the most obvious allergen source, according to Matthew Zirwas, MD, of Bexley Dermatology, who presented a case-based session at Maui Derm NP+PA Summer 2026 in Colorado Springs.1 In an interview with HCPLive, Zirwas walked through 2 cases that illustrate how comprehensive patch testing reveals unexpected drivers and guides management when standard therapies have stalled.

Paraphenylenediamine in an Automotive Factory Worker

The first case involved a patient with hand eczema working in an automotive factory who had not responded adequately to topical therapy. Comprehensive patch testing returned positive for roughly half a dozen allergens, but 1 stood out as the likely driver: paraphenylenediamine (PPD).

PPD is most commonly recognized as a hair dye allergen, but it is also used in the production of rubbers, plastics, automotive components, and industrial products.2,3 In this patient's case, a PPD-related compound was present in the lubricant used on factory parts, and the patient's gloves had become saturated with it, creating prolonged occlusive contact with the allergen.

"That gave us the answer in that one," Zirwas said.

Facial Dermatitis Persisting After CSU Treatment

The second case centered on a woman with chronic spontaneous urticaria (CSU) who had been started on antihistamines and subsequently remibrutinib, a BTK inhibitor. Nearly all of her disease cleared except for a persistent facial dermatitis with a mildly urticarial quality that did not present purely as hives.

Patch testing identified sensitization to multiple allergens, including fragrance, acrylates, gold, and nickel. She was enrolled in the contact allergen management program, a structured resource helping patients identify safe products based on their specific sensitization profile, and her facial dermatitis resolved. The precise culprit among the positive allergens was never definitively identified.

"We don't know which of those allergens ended up being the thing, whether it was the fragrance or the acrylates from nails or gold," Zirwas said. "To some extent we don't care. What we care about is that she’s better.”

A Framework Behind the Cases

Both cases reflect a broader clinical evolution Zirwas described across his session. He now positions patch testing as a later step rather than a first-line tool, reserving it for patients who have not responded to empiric avoidance and an IL-13 inhibitor trial. When the distinction between allergic contact dermatitis and atopic dermatitis remains unresolved, he said a biologic trial can itself clarify the diagnosis, since biologics do not meaningfully help isolated allergic contact dermatitis. For patients where getting them better takes priority over resolving the diagnostic question, he prefers a JAK inhibitor, which he said works regardless of which condition is driving the disease.

He also identified nickel and ammonium persulfate as the 2 allergens most frequently missed in routine eczematous workups, noting that dietary nickel and hot tub exposure, respectively, are the sources clinicians are most likely to overlook.

In earlier parts of this interview, Zirwas discussed using IL-13 inhibitor response to guide patch testing decisions in eczematous dermatitis, how delgocitinib fills a long-standing gap in chronic hand eczema treatment, and how overlapping allergic contact dermatitis changes his biologic or JAK inhibitor selection approach.

Editor’s note: Reported disclosures for Zirwas include GENZYME CORPORATION, Regeneron Healthcare Solutions, Dermavant Sciences, and more.

References

1. Zirwas M. Eczematous and Contact Dermatitis: Cases That Will Leave You Scratching Your Head. Session presented at Maui Derm Summer 2026 in Colorado Springs on June 24.

2. Mukkanna KS, Stone NM, Ingram JR. Para-phenylenediamine allergy: current perspectives on diagnosis and management. J Asthma Allergy. 2017;10:9-15. Published 2017 Jan 18. doi:10.2147/JAA.S90265

3. Mao T, Liu W, Deng J, et al. p-Phenylenediamines and p-phenylenediamine quinone derivatives in rubber consumer products and typical urban dust: Sources, transformation profiles, and health risks. Environ Int. 2024;192:109042. doi:10.1016/j.envint.2024.109042