Definition. Blebs are vesicles of greater dimensions, being pea-to egg-sized or larger, rounded or irregularly shaped, tense or flaccid, epidermis elevations with serous or seropurulent contents.
Blebs are often formed by the coalescence of vesicles and like vesicles they usually originate in the deep and middle layers of the epidermis. But they differ from vesicles in presenting stronger roof-walls, less tendency to spontaneous rupture, longer duration, greater freedom from subjective sensations, being more frequently seated in apparently normal skin, and indicating a graver systemic condition. Blebs may contain serum, pus, blood or lymph; may be tense or flaccid; and may terminate in a similar manner as vesicles, by rupture, desiccation, pustulation, ulceration, and crusting. In shape, bullae may be oval, hemispherical, crescentric, round or irregular from coalescence of a number of lesions. Single bulla vary in size from a pea to a goose egg; but when confluent, they sometimes form enormous lesions. Blebs are diagnostic of pemphigus, herpes iris and pompholyx; and may appear in the course of cutaneous syphilis, erysipelas, urticaria, erythema multiforme and exceptionally in almost any inflammation of the skin.