Herpetic dermatitis (e.g., herpes simplex or zoster) is characterized by grouped vesicles on an erythematous base. Erysipelas, in its classic form, is a diffuse erythematous plaque without vesicles. | Unilateral distribution (A) may suggest herpes zoster but is not distinctive for erysipelas vs. herpes. | Edema (B) is present in both conditions. | Pain (C) is present in both, though burning neuropathic pain is more common in herpes. | Fever (E) may be present in both, but is more common in erysipelas. | Consult dermatology or infectious diseases when complicated herpes zoster is suspected (e.g., eye, ear, or trigeminal nerve involvement) to initiate antiviral therapy early. | Presence of vesicles changes diagnosis from erysipelas to viral (herpetic) infection. | Facial herpes zoster (especially V1 trigeminal distribution) requires eye examination to exclude corneal involvement (Herpes Zoster Ophthalmicus). | Sources: Scott Browns Otorhinolaryngology 8th edition volume 3 — pp. 27, 388; Controversies in Otolaryngology — pp. 5, 124.