Impetigo is caused by streptococcus (strep) or staphylococcus (staph) bacteria. Methicillin-resistant staph aureus (MRSA) is becoming a common cause.
The skin normally has many types of bacteria on it, but intact skin is an effective barrier that keeps bacteria from entering and growing in the body. When there is a break in the skin, bacteria can enter the body and grow there, causing inflammation and infection. Breaks in the skin may occur with:
Injury or trauma to the skin
Impetigo may also occur on skin where there is no visible break.
It is most common in children, particularly those in unhealthy living conditions.
In adults, it may follow other skin disorders or a recent upper respiratory infection such as a cold or other virus. It is similar to cellulitis, but it only involves the top layers of the skin.
Impetigo is contagious, meaning it can spread to others. You can catch this infection if the fluid that oozes from the blisters touches an open area on your skin.
A single or possibly many blisters filled with pus; easy to pop and -- when broken -- leave a reddish raw-looking base (in infants)
Filled with yellow or honey-colored fluid
Oozing and crusting over
Rash -- may begin as a single spot, but if person scratches, it may spread to other areas
Skin lesions on the face, lips, arms, or legs, that spread to other areas
Swollen lymph nodes near the infection (lymphadenopathy)
Signs and tests
Diagnosis is based mainly on the appearance of the skin lesion.
A culture of the skin or lesion usually grows the bacteria streptococcus or staphylococcus. The culture can help determine if MRSA is the cause, because specific antibiotics are used to treat this infection.
The goal is to cure the infection and relieve the symptoms.
A mild infection may be treated with a prescription antibacterial cream. More severe cases may require antibiotics, taken by mouth.
Wash (do not scrub) the skin several times a day, preferably with an antibacterial soap, to remove crusts and drainage.
The sores of impetigo heal slowly and seldom scar. The cure rate is extremely high, but the condition often comes back in young children.
Pasternack MS, Swartz MN. Cellulitis, necrotizing fasciitis, and subcutaneous tissue infections. In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2009:chap 90.
Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.