Bullous pemphigoid (BP)

Bullous pemphigoid affects the skin, most often in older adults. The immune system produces antibodies against BP180 and BP230, two proteins that help anchor the outer layer of skin to the layer beneath it, and most patients' antibodies target a specific region of BP180 called the NC16A domain. As that anchoring breaks down, fluid separates the skin layers and forms tense blisters, with complement activation and the buildup of eosinophils and neutrophils driving much of the surrounding inflammation. Research also points to a type 2 immune signature in many cases, including elevated IgE and eosinophil activity in the affected skin.

Bullous pemphigoid is described as the most common subepidermal blistering disease, though it remains uncommon overall, with global incidence estimated at well under one new case per 1,000 person-years, concentrated heavily in people over 70.

Common signs

Large, tense, fluid-filled blisters, often on the arms, legs, trunk, and skin folds, frequently preceded by intense itching and red, hive-like or eczema-like patches. The blisters tend to be firm rather than easily broken, and the mouth is involved less often than in some other blistering conditions, such as pemphigus vulgaris. Healed skin usually clears without scarring.

This is a plain-language summary for orientation, not a diagnosis. Mechanisms are described as current understanding, not settled fact. Work with your own clinician for your care.