Impetigo is broadly classified into three forms. Non-bullous impetigo, accounting for more than 70% of cases, is the most common; it starts around the nose and mouth, with small blisters that rupture and leave honey-colored crusts. Bullous impetigo, caused by toxins from Staphylococcus aureus, splits the skin to form large blisters that, once ruptured, leave thin crusts; it tends to appear more on the trunk and limbs. Ecthyma is a more severe form in which the infection penetrates into the deeper skin layers, forming ulcers beneath the crust that may leave scars and requiring a longer course of antibiotic treatment.