Impetigo is a skin infection, caused by Staphylococcus aureus, Streptococcus pyogenes, or both, that leads to the formation of scabby, yellow-crusted sores and, sometimes, small blisters filled with yellow fluid.
Impetigo is common. It affects mostly children. Impetigo can occur anywhere on the body but most commonly occurs on the face, arms, and legs. The blisters that may form (bullous impetigo) can vary from pea-sized to large rings and can last for days to weeks. Impetigo often affects normal skin but may follow an injury or a condition that causes a break in the skin, such as a fungal infection, sunburn, or an insect bite. Poor hygiene and a moist environment are also risk factors. Some people have Staphylococcus bacteria living in their nose without causing disease (they are considered nasal carriers). These nasal bacteria may cause repeat infection in the person and sometimes in others.
Impetigo is itchy and slightly painful. The itching often leads to extensive scratching, particularly in children, which serves to spread the infection. Impetigo is very contagious—both to other areas of the person's own skin and to other people. Impetigo typically causes clusters of sores to rupture and develop a honey-colored crust over the sores. Bullous impetigo is similar except that the sores typically enlarge rapidly to form blisters. The blisters burst and expose larger bases, which become covered with honey-colored varnish or crust.
Doctors base the diagnosis on the appearance of the rash. In people who have repeated infections, a swab of the nose is taken and sent to the laboratory to determine whether they are a nasal carrier of staphylococci.
The infected area should be washed gently with soap and water several times a day to remove any crusts. Small areas are treated with topical antibiotics. If large areas are involved, an antibiotic taken by mouth may be needed. People who are nasal carriers are treated with topical antibiotics applied to the nasal passages.
Last full review/revision October 2007 by A. Damian Dhar, MD, JD