In impetigo contagiosa, the lesions begin with a single 2-4 mm erythematous macule that rapidly evolves into a vesicle or a pustule. The infection spreads to contiguous and distal areas through inoculation of other wounds from scratching. Bullous impetigo presents with small or large, superficial, fragile bullae on the trunk and the extremities. Often, only the remnants of ruptured bullae are seen at the time of presentation. The separation of the epidermis is due to an exotoxin produced by staphylococci, which may be the only organism present in cases of bullous impetigo.
Common impetigo is the term applied when the infection occurs in preexisting wounds.
Impetigo also can present as folliculitis, which is considered to be impetigo of the hair follicles caused by S aureus . Ecthyma is a deeper, ulcerated impetigo infection, often occurring with lymphadenitis. The histology of the lesions in all presentations will reveal a subcorneal neutrophilic infiltrate. S aureus is cultured consistently from the lesions, but streptococci are found only occasionally. The infection may be caused by a mixture of the two organisms.