Please help! what is the origin of cellulitis?

Many Causes: 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.

Many possibilities : There are various things that could case a cellulitis. The infections can result from fungus, bacterial or due to a virus. Have it evaluated by a professional to get the appropriate treatment.