Patients classically present with the triad of pain, swelling and erythema. The most consistent feature of early NF is that the pain is out of proportion to the swelling or erythema. Other important features that make NF likely are:

• Tenderness extending beyond the apparent involved area
• Indistinct margins of involvement
• Absence of lymphangitis  (because the infection is in the deep fascia and not in the skin)
• Rapidly progressive despite the use of antibiotics
• If the patients looks too sick for cellulitis
• Bleb/Bullae, Crepitus (Though you cannot not rule out NF in their absence)