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Dermatophytid Reaction

(Identity Reaction or Id Reaction)

By

Denise M. Aaron

, MD, Dartmouth Geisel School of Medicine

Last full review/revision Feb 2020| Content last modified Feb 2020
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A dermatophytid reaction is the body's reaction to a dermatophyte (fungal) infection and is a skin eruption that appears on an area of the body that is not the area where the infection first began.

A dermatophytid reaction is not actually a type of dermatophytosis Overview of Dermatophytoses (Ringworm, Tinea) Dermatophytoses are fungal infections of the skin and nails caused by several different fungi and classified by the location on the body. Dermatophyte infections are also called ringworm or... read more . Rather, a fungal infection on one area of the body can cause an allergic skin eruption to appear on another area of the body that is not infected. For example, a fungal infection on the foot may cause an itchy, bumpy rash to appear on the fingers. These eruptions (dermatophytids, also called identity or id reactions) are allergic reactions to the fungus. They do not result from touching the infected area. The eruptions may appear on many different areas of the body at once.

The eruptions are typically itchy. They may appear as

Doctors base the diagnosis of dermatophytid reactions on an examination of skin scrapings Scrapings Doctors can identify many skin disorders simply by looking at the skin. A full skin examination includes examination of the scalp, nails, and mucous membranes. Sometimes the doctor uses a hand-held... read more Scrapings . Scrapings taken from the areas that have the dermatophyte infection show the fungus, but scrapings taken from the areas that have the dermatophytid reaction do not. This combination of findings indicates that the second (separate) eruption is a dermatophytid reaction.

The dermatophytid reaction goes away once the dermatophyte infection has been cured. To relieve symptoms of dermatophytid reactions, doctors give corticosteroid creams, anti-itch drugs taken by mouth (such as hydroxyzine), or both.

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