(bul'ah) (Latin. Bulla - a round swelling, a bubble)
A bulla is a circumscribed elevation of skin of 0.5 cm or more in diameter containing a liquid. The distinction between vesicle and bulla is arbitrary and depends only on size (vesicles are less than 0.5 cm).
Examples of bullae:Dermal bulla
A bulla caused by separation of tissue components of the dermis with collection of serous fluid.
Example: dystrophic epidermolysis bullosa
A blister formed within the epidermis by pathologic change in epidermal cells or cellular cohesion.
Example: miliaria crystallina
An intraepidermal multilocular vesicle or blister formed by separation of epidermal cells by edema. Lymphocytes predominate in allergic contact dermatitis and neutrophilic leukocytes predominate in irritant dermatitis.Subcorneal bulla
A bulla formed by exudate beneath the stratum corneum, and above the stratum spinosum.
Example: bullous impetigo
A vesicle or bulla formed by cleavage of the dermal-epidermal interface and with the roof of the bulla composed of the epidermis.
Example: bullous pemphigoid