What are possible complications of impetigo?

Usually none. Impetigo usually resolves completely with proper treatment. Without treatment, it can spread to other parts of the body. Scarring of the skin is uncommon, but can happen. When strep is the cause of the infection, a very rare kidney problem can develop. Taking antibiotics for the infection can help prevent these complications.
Spread . Can spread elsewhere on the skin, to deeper tissues (cellulitis, abcess, lymphangitis, blood infection) respiratory infection, kidney inflammation (glomerulonephritis) rheumatic fever if respiratory involvement. Also can spread to other members of the household and family.