bullous

Bullous is a medical term used to describe conditions in which blisters, or bullae, form on the skin or mucous membranes. A bullae is a circumscribed, fluid-filled lesion larger than 1 cm in diameter, whereas smaller fluid-filled lesions are called vesicles. The term derives from Latin bulla, meaning bubble.

Bullous conditions can arise from autoimmune disease, infection, genetic disorders, or mechanical injury. Notable examples include bullous pemphigoid, an autoimmune subepidermal blistering disease that typically affects older adults and presents with tense bullae that heal without extensive scarring; pemphigus vulgaris, another autoimmune condition characterized by fragile, intraepidermal bullae and frequent mucosal involvement; and bullous impetigo, a contagious bacterial infection in children that causes superficial, rupture-prone blisters.

Pathophysiology varies by disease. In bullous pemphigoid, autoantibodies target basement membrane proteins (BP180, BP230), causing separation at the dermal-epidermal junction. In pemphigus vulgaris, antibodies against desmogleins disrupt cell adhesion within the epidermis. Genetic or mechanical blistering disorders, and infectious etiologies, can produce bullae through different mechanisms.

Diagnosis relies on clinical examination supported by skin biopsy with histology and direct immunofluorescence, which helps distinguish bullous disorders. Additional tests may include serology and culture for infections.

Treatment is disease-specific, ranging from topical wound care and antibiotics for secondary infection to systemic corticosteroids and immunosuppressants for autoimmune forms; newer therapies such as targeted biologics are used in some cases. Prognosis depends on the underlying condition and response to therapy.