Cellulitis — Erysipelas Sharp Border Plaque

A 52-year-old man from rural Maharashtra presents with acute onset fever, chills, and a rapidly spreading erythematous plaque on his left lower leg. On examination, the lesion is raised, warm, tender, and edematous. The feature marked **B** in the diagram — the sharp, distinct border separating the inflamed skin from normal skin — is a hallmark finding. Which of the following best explains why erysipelas characteristically presents with this sharply demarcated border, in contrast to cellulitis?