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. Ecthyma is a form of impetigo that causes sores deeper in the skin.
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) vary in size 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 staphylococci or streptococci 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 and ecthyma are 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 tiny blisters that rupture and develop a honey-colored crust over the sores. Bullous impetigo is similar except that the sores typically enlarge rapidly to form larger blisters. The blisters burst and expose larger bases, which become covered with honey-colored varnish or crust.
Ecthyma is characterized by small, shallow ulcers that have a punched-out appearance and often contain pus. The crust that covers the ulcers in thicker than the crust caused by impetigo. It is brown-black in color. The area around the ulcers is typically purplish red and swollen.
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 or streptococci.
The infected area should be washed gently with soap and water several times a day to remove any crusts. Small areas are treated with antibiotic ointments or creams applied directly to the skin (topically). If large areas are involved or are not cured with topical antibiotics, 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 July 2013 by A. Damian Dhar, MD, JD