Circumscribed collections of fluid in the skin are termed blisters or blebs (roughly up to 1 cm) or bullae (roughly upwards of 1 cm). They may be subcorneal (e.g. impetigo contagiosa, pemphigus foliaceus), intra-epidermal (e.g. pemphigus vulgaris, epidermolysis bullosa simplex), junctional (e.g. bullous pemphigoid) or subepidermal (epidermolysis bullosa dystrophica). Puss-filled vesicles are termed pustules. Impetigo contagiosa is by far the most common vesicle-forming disease seen in children. As a rule,the diagnosis and treatment are unproblematic. At the latest when suitable therapy fails to elicit a response and/or in the absence of pyogens, the less common differential diagnoses must be considered.