Dermatophytid Reaction

ByDenise M. Aaron, MD, Dartmouth Geisel School of Medicine
Reviewed/Revised Sept 2023
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Dermatophytid reaction is an inflammatory reaction to dermatophytosis at a cutaneous site distant from the primary infection. Diagnosis is by potassium hydroxide wet mount. Treatment depends on the primary dermatophytosis.

Dermatophytid (identity or id) reactions are protean; they are not related to localized growth of the fungus but rather are an inflammatory reaction to a dermatophytosis elsewhere on the body.

Lesions are typically pruritic and may manifest as

Distribution may be extensive.

Erythema Annulare Centrifugum
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This photo shows annular and arcuate lesions of erythema annulare centrifugum.
Image courtesy of Karen McKoy, MD.
Dermatophytid Reaction
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This dermatophytid (identity, or id) reaction manifests as copious vesicles on the fingers.
Image courtesy of CDC/Dr. Lucille K. Georg via the Public Health Image Library of the Centers for Disease Control and Prevention.

Diagnosis of Dermatophytid Reaction

  • Potassium hydroxide wet mount

Diagnosis of dermatophytid reaction is by potassium hydroxide wet mounts that are negative at the site of the id reaction and positive at the distant site of dermatophyte infection.

Treatment of Dermatophytid Reaction

  • Treatment of the primary dermatophytosis

Options for Treatment of Superficial Fungal Infections).

Drugs Mentioned In This Article
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