By Gary M. White, MD
Id reaction shown here on the arm as a result of a primary inflammatory condition on the leg.
An id reaction is an eczematous reaction that occurs at a site distant to the location of a prior existing inflammatory rash. Stasis dermatitis and kerion celsi are common primary causes of this secondary eczematization.
Itchy, eczematous papules are typical. The id reaction commonly affects the palms or upper extremities, but may occur in a widespread distribution. An id reaction may occur in patients with tinea capitis. Dermatophytid reactions are defined as secondary eruptions in response to dermatophytosis [Pediatr Dermatol 2015 Feb 12 ahead of print]. They are most common in patients with kerion celsi. Eczematous scaly patches or plaques are typical. They occur unrelated to any therapy.
Treating the primary cause is paramount. The id reaction will respond to steroids, topical or systemic.
The first image shows an id reaction from stasis dermatitis (notice the wrap).
Here, a gram-negative toe web infection is causing an id reaction on the palms.
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