Your pathology report for interface dermatitis

by Jason Wasserman MD PhD FRCPC and Zuzanna Gorski MD
July 21, 2025

Interface dermatitis is a term pathologists use to describe a pattern of skin injury seen under the microscope. It refers to inflammation and damage that occurs at the junction where the outer layer of the skin (called the epidermis) meets the layer underneath (called the dermis). This area is known as the dermoepidermal junction.

In interface dermatitis, the inflammation is usually caused by the body’s immune system attacking the skin. The immune cells specifically target the basal cells, which are the bottom layer of cells in the epidermis. These basal cells normally help regenerate the skin, but in interface dermatitis, they are injured or destroyed, often appearing vacuolated (damaged and empty looking) or completely missing.

What causes interface dermatitis?

Interface dermatitis is not a disease on its own. Instead, it describes a reaction pattern seen in several different skin conditions. The most common causes include:

  • Autoimmune diseases such as lupus erythematosus, dermatomyositis, or graft-versus-host disease.

  • Lichen planus and other lichenoid (lichen-like) skin conditions.

  • Viral infections or drug reactions (especially reactions to antibiotics or anti-seizure medications).

  • Erythema multiforme, a condition often triggered by infections or medications.

Some types of cutaneous T-cell lymphoma, such as early mycosis fungoides, can also show interface dermatitis.

What does interface dermatitis look like under the microscope?

Under the microscope, interface dermatitis shows:

  • Damage to the basal cells at the bottom of the epidermis. These cells may appear pale, swollen, or dying.

  • Inflammatory cells, mostly lymphocytes (a type of white blood cell), gathering along the dermoepidermal junction.

  • Sometimes, dead skin cells called necrotic keratinocytes or Civatte bodies are seen in the epidermis.

  • In more severe cases, the inflammation is strong enough to obscure the junction between the two layers of the skin.

There are two main types:

  • Cell-poor interface dermatitis, where the inflammation is mild and mostly limited to the dermoepidermal junction. This is common in conditions like lupus or dermatomyositis.

  • Cell-rich (lichenoid) interface dermatitis, where a dense band of immune cells accumulates at the junction and causes more visible damage. This is common in lichen planus and some drug reactions.

Why is interface dermatitis important in a pathology report?

When interface dermatitis is seen in a skin biopsy, it gives doctors a clue about the possible cause of the patient’s symptoms. It helps narrow down the list of conditions being considered (the differential diagnosis).

Because many different conditions can cause interface dermatitis, the pathologist will look closely at the pattern of inflammation, the presence of dead or damaged cells, and other microscopic features to help identify the underlying cause. This information is then combined with clinical findings (such as symptoms and blood test results) to make a diagnosis.

What conditions are associated with interface dermatitis?

Some of the most common conditions associated with interface dermatitis include:

  • Systemic lupus erythematosus (SLE).

  • Dermatomyositis.

  • Lichen planus.

  • Erythema multiforme.

  • Graft-versus-host disease.

  • Drug reactions.

  • Pityriasis lichenoides.

  • Viral exanthems.

  • Early cutaneous T-cell lymphoma (mycosis fungoides).

Each condition has its own unique clinical and microscopic features that help the pathologist and treating physician arrive at a final diagnosis.

Questions to ask your doctor

  • What condition is causing the interface dermatitis in my skin biopsy?

  • Do I need further testing or treatment based on this finding?

  • Are there any signs of autoimmune disease or drug reaction?

  • Should I stop taking any medications that might be contributing?

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