How to tell if cellulitis is not healing?

Simple: If you are not getting better, decreased pain erythema temperature etc, then the cellulitis is not resolving.

Continued symptoms: Continued pus, pain, fever, bright-red color, tenderness are bad.

What's the cause ?: Cellulitis is basically a visible inflammation (itis) of the skin and soft tissues (red, hot, swollen and tender) . It can be caused by many things including sunburn (radiation), trauma (sprained ankle) or poor vein circulation (stasis dermatitis). It need not be caused by bacteria. If you have repeated episodes of this, get to a wound care or vascular specialist, the diagnoses you have is wrong.