Abstract
Background
Nummular eczema (NE) is a prevalent and chronic inflammatory dermatosis marked by pruritic, coin-shaped eczematous plaques. Contact allergen sensitization may play a role in NE etiology.Methods
On April 30, 2026, PubMed, Embase, and the Cochrane Library were searched per PRISMA guidelines for studies investigating triggers or aggravators of NE through patch testing.Results
Of 287 studies identified, 10 observational studies met the inclusion criteria. The median overall patch test positivity among patients with NE was 47.8% (range: 26.7% to 56.0%). The most frequently reported allergens included nickel and nickel sulfate, potassium dichromate, cobalt chloride, fragrance mix, neomycin, colophony, formaldehyde, paraphenylenediamine, and rubber-related allergens. Among studies reporting concomitant allergic contact dermatitis (ACD), a median of 33.5% of patients with NE had concurrent or prior ACD.Conclusions
Available observational evidence suggests that contact allergen positivity is common among patients with NE. Patch testing should be considered for patients with severe or treatment-refractory NE to identify clinically relevant allergens and guide trigger-avoidance strategies. Further studies using standardized patch testing protocols and assessments of clinical relevance are needed to clarify whether contact sensitization is an etiologic factor, a disease aggravator, or a comorbid finding in NE.  .