Representative ultrasonic images. One representative case from each group is provided: “erythema – pigmentation” in the non-severe group (A), “erythema–keratin peeling” in the non-severe group (B), “localized erosion–epithelialization” in the severe group (C), and “widespread erosion–crusting” in the severe group (D). The color scale of echogenicity is white-yellow-red-green-blue-black. a, epidermis, b, dermis, c, zonal hypoechoic areas in papillary dermis (SLEB grade 3). (C) and (D) Lower dermis echogenicity than (A) and (B) (P = 0.036). Only (D) has a SLEB grade of 3. SLEB, subepidermal low echogenic band.