Impetigo is a contagious skin infection most often seen in children. It causes red, oozing, and crusty sores. The infection can spread to other parts of the body if you scratch the sores. Impetigo is caused by streptococcus (strep) or staphylococcus (staph) bacteria. Follow the links below to find WebMD's comprehensive coverage about how impetigo is contracted, what it looks like, how to treat it, and much more.