impetigo (EFO_1000714) is a pyoderma consisting of three forms of skin lesions having either a thick, adherent, recurrent, dirty yellow crust with an erythematous margin (common or superficial impetigo) or lessions which are superficial, thin-walled, and bullous as found in bullous impetigo. The lesions in bullous (staphylococcal) impetigo, which are always caused by S aureus, are superficial, thin-walled, and bullous.