What is an Id Reaction?

Most commonly a reaction to a superficial fungal infection

Contact Dermatitis. Credit: BSIP / Contributor / Getty Images

An interface dermatitis (ID) reaction, also known as autoeczematization, is an itchy rash with blisters, or vesicles. It usually occurs on the sides of the fingers, but it can also be found on the chest or arms. 

What Does An Id Reaction Look Like?

An id reaction can present itself in a variety of ways. Examples include:

  • localized or widespread vesicular lesions (a vesicle is a small, fluid-filled spot)
  • maculopapular or scarlatiniform eruptions (red patches with red bumps
  • erythema nodosum (deep, raised, bruise-like areas on the shins )
  • erythema multiforme (pinkish red spots that resemble targets)
  • guttate psoriasis (light pink teardrop shaped bumps)

What Causes An Id Reaction?

The most common cause of id reactions is a fungal infection somewhere else on the body, especially athlete's foot. But it may also occur because of bacterial, viral, or parasitic infections. Id reactions can also occur to therapies. 

Id is also typically seen in autoimmune skin disorders such as lichen planus, cutaneous lupus erythematosus, and may also appear during immune reactions against drugs, viruses, and tumors. For instance, one study found that id reactions occurred to bladder cancer patients undergoing BCG therapy.

How Is An Id Reaction Treated?

How the id reaction is treated depends on what caused it in the first place.

Your dermatologist will want to identify the underlying infection, and they do this by taking scrapings of the area affected.

Basically, the id reaction is thought to be an allergic response to fungi (or bacteria, or virus, or parasite) and treating the fungal infection makes the id reaction rash go away.

 Sometimes an id reaction is the only way a person knows they have an infection. To relieve symptoms, your doctor may prescribe corticosteroid creams or oral anti-itch drugs.

Common Infections That Cause Interface Dermatitis

While an id reaction may occur for numerous reasons, here are some of the more common infections that trigger it:

  • Ringworm—also known as tinea corporis and tinea capitis. It is actually not caused by a worm, but by fungi.
  • Athlete's foot—also known as tinea pedis.
  • Jock Itch—also known as tinea cruris. It is a fungal infection of the skin in the groin.
  • Spider Bites
  • Tinea Versicolor—also known as pityriasis versicolor. It is a superficial fungal infection of the skin that is often confused with other common rashes.
  • Intertrigo— a yeast infection of skin folds caused by Candida albicans.

Sources:

Aaron DM. Dermatophytid Reaction. Merck Manual: Consumer Version.

Ilkit M, Durdu M, Karakaş M. Cutaneous id reactions: a comprehensive review of clinical manifestations, epidemiology, etiology, and managementCrit Rev Microbiol. 2012 Aug;38(3):191-202.

Joshi R. Interface dermatitisIndian J Dermatol Venereol Leprol. 2013 May-Jun;79(3):349-59.

Lowther C, Miedler JD. Cockerell CJ. Id-like reaction to BCG therapy for bladder cancer.Cutis. 2013 Mar;91(3):145-6, 151.

Wenzel J. Tüting T. An IFN-associated cytotoxic cellular immune response against viral, self-, or tumor antigens is a common pathogenetic feature in "interface dermatitis." J Invest Dermatol. 2008 Oct;128(10):2392-402. 

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