What Is an Interface Dermatitis (ID) Reaction?

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Interface dermatitis (ID) is a reaction characterized by an itchy rash with small, water-filled blisters. It usually appears on the sides of your fingers. ID is not one disease, but rather a result of an immunological insult or allergic reaction that occurs somewhere else on your body. For example, a fungal infection on your foot activates your immune system, and your immune response triggers ID.

Interface dermatitis gets its name because it occurs in a specific area of the skin—the dermo-epidermal junction, a.k.a. the interface. This sits between the outermost layer of skin (epidermis) and the middle layer (dermis).

Interface Dermatitis Symptoms

Interface dermatitis typically involves some or all of the following:

  • Vesicular lesions: Small fluid-filled spots that can be just in one area or widespread
  • Maculopapular or scarlatiniform eruptions: Red patches with raised red bumps
  • Erythema nodosum: Deep, raised, bruise-like areas on the shins
  • Sweet's syndrome: Fever and painful lesions on the head, neck, trunk, and arms
  • Guttate psoriasis: Small, tear-shaped spots/bumps that are red and scaly; most common in children and young adults
  • Erythema multiforme: Pinkish red spots that resemble targets

Regardless of where the cause initiated, the ID response most often occurs on the sides of the fingers. In some cases, it's on the chest or arms.

Associated itching can often be quite intense.

Examples of Appearance

An ID reaction can vary in appearance from one person to the next because the underlying cause can differ.

This photo contains content that some people may find graphic or disturbing.

erythema nodosum
Erythema nodosum on the legs. DermNet / CC BY-NC-ND

This photo contains content that some people may find graphic or disturbing.

erythema multiforme
Erythema multiforme of the hands.  DermNet / CC BY-NC-ND

This photo contains content that some people may find graphic or disturbing.

Guttate psoriasis
Guttate psoriasis on the back. DermNet / CC BY-NC-ND

Causes

ID is believed to be caused by a reaction similar to an autoimmune disease, in which your immune system, essentially, misfires.

Research suggests that, with interface dermatitis, T cells from the immune system become auto-aggressive. In other words, your own cells attack you and target the lower portion of the epidermis (the basement membrane).

Why certain illnesses or drugs trigger auto-aggressive T cells in some people is not yet understood. Fungal infections are the most common triggers, including:

However, interface dermatitis can also occur as a result of a bacterial, viral, or parasitic infection, tumors, or even drugs. Spider bites have even been associated with ID.

In some cases, an interface dermatitis reaction may be the first sign of an infection that needs to be treated.

Some people may also develop interface dermatitis as a response to allergic contact dermatitis, a condition that occurs when your skin comes into contact with an allergen. Contact dermatitis causes an itchy, red rash—sometimes with bumps, blisters, or cracked skin—right where the contact occurred.

Interface dermatitis is also typically seen with:

Several other diseases that are inflammatory, infectious, or cancerous may involve interface changes, as well.

While an ID reaction rash cannot be passed from one person to the next, the primary condition that gave rise to the reaction may be contagious.

Diagnosis

When you have any type of dermatitis, it can be difficult for your doctor to determine which one it is because many types have the same or highly similar symptoms. Many other skin diseases may have a similar presentation, as well.

Skin problems that may appear similar to ID include:

If the underlying cause is evident, your doctor may diagnose ID based on appearance alone. But given the above, testing is often needed.

Research suggests that interface dermatitis is most accurately diagnosed based on the confirmed presence of a condition associated with ID reactions, as well as a skin biopsy to confirm the involvement of the dermo-epidermic junction and to rule out certain types of dermatitis.

To determine the underlying condition, if one isn't obvious, your doctor may perform:

  • Scrapings from the affected area
  • Skin culture for bacteria, fungus, or virus
  • Allergy skin testing to rule out contact dermatitis
  • Blood tests for signs of systemic disease

Treatment

How an interface dermatitis reaction is treated depends largely on what caused it in the first place.

ID reactions due to an infection or allergic reaction generally go away when the cause is resolved.

If the cause is a long-lasting illness, such as an autoimmune disease, you may get relief through treatments for that disease or direct treatment of ID symptoms.

Treatments used to reduce ID symptoms themselves include:

  • Corticosteroid cream
  • Oral steroids
  • Antihistamine creams, if an allergic response is suspected or confirmed
  • Oral antihistamines, if an allergic response is suspected or confirmed

Possible Future Drug Treatments

A promising new treatment is a biologically produced protein called serpina3n. In animal studies, it has both prevented and treated ID reactions. More work will need to be done before this treatment can be considered safe and effective in humans.

A newer class of immunosuppressants called Janus kinase (JAK) inhibitors is also being looked at as a possible ID treatment. Several JAK inhibitors are already on the market, so if studies remain positive, they may eventually start being prescribed off-label for ID.

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