Is there any otc medicine for cellulitis?

Not really: Kinda depends on the cause-- true cellulitis represents an infection of the skin and so needs antibiotics. Occasionally you can improve the inflammation aspect with some otc steroid cream and oral antiinflammatory agent like ibuprofen, but really need antibiotics. If it is a dermatitis, which some may confuse with a cellulitis, then the cream etc may suffice.

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.

Depends: If you have cellulitis and it is not serious then maybe one can get a way with soap water and antibiotic cream. Most of the cellulitis that i see and treat require either IV or PO antibiotics and aggressive wound care.