Impetigo infection on an upper lip. This is a highly contagious bacterial skin infection caused by IStaphylococcus i bacteria. This infection is particularly common in babies and children, occurring mainly on the face and limbs. The infection starts as a red patch and develops into small pustules that join together, forming a yellow, crusty sore. Victims must not share any items which come into contact with the affected area, such as towels, as this will spread the infection. Impetigo is treated locally with antibiotic drugs. The infection heals within seven to ten days.