The differences between acute cellulitis and erysipelas are as follows:

Acute cellulitis is an acute diffuse purulent infection of the subcutaneous, subfascial, intramuscular space, or deep cellular tissue. It is characterized by the difficulty in localizing the lesion, rapid spread, and no obvious boundary with normal tissue. The main pathogen is Streptococcus hemolyticus, followed by Staphylococcus aureus, and it can also be caused by anaerobic bacilli.

Erysipelas is an acute inflammation of the skin and its reticular lymphatic vessels, caused by the invasion of β-hemolytic streptococcus through small wounds in the skin and mucous membranes. Erysipelas spreads rapidly, and there is rarely tissue necrosis or suppuration. The most commonly affected areas are the lower extremities and the face. The onset is sudden, and patients often experience headache, chills, and fever. The local manifestation is a patchy red rash, bright red in color, lighter in the middle, with a clear and slightly elevated border. Gentle pressure with a finger can make the redness fade, but the redness quickly returns after the pressure is removed.