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Cold Sores vs. Impetigo

Harvard Health Publications
2007 Copyright Harvard Health Publications


My daughter has sores on her mouth. How can I tell the difference between cold sores and impetigo?


This is a common question because both impetigo and cold sores can look like blisters, crust over as they heal, and are located around the mouth, making it hard to tell the difference between the two.

Impetigo, a skin infection caused by bacteria, begins as small fluid-filled blisters on the skin, which then break open, showing redness of the skin and leaking clear fluid. Soon after, a honey-colored crust develops over the area before it finally heals, which takes at least one to two weeks. Although impetigo can be found anywhere on the body, it is most common around the lips and nose. It can be itchy, but usually is not painful. Since it is contagious (spread from one person to another), keep the area clean and dry. It would help if your child does not scratch or touch the area, and washes the hands well and often. Impetigo can be treated with a topical antibiotic. If the infection seems to be spreading or involves many areas of the body, your child may need to take an oral antibiotic to clear it up.

On the other hand, cold sores, a skin infection caused by a virus (the herpes simplex virus), look like small reddish blisters and are most often found on or around the lips, or at the corners of the mouth. They usually go away on their own over a couple of weeks, scabbing over as they heal. Since these also are spread person to person by touching or direct contact with the rash, make sure not to kiss, or share glasses, eating utensils, towels, or washcloths with someone if you have cold sores. Unlike impetigo, cold sores can be quite painful, especially during the first few days they appear. You can apply ice to the area or take over-the-counter pain medications such as acetaminophen or ibuprofen.

Unfortunately, there is no medication to cure cold sores. Kids with cold sores may continue to get them, usually in the exact same spot, for the rest of their lives. The herpes virus stays in the body and can come out at any time to cause a cold sore. Stress, illness, not enough sleep, and sun exposure all can cause the cold sore to come back. There is medication that your doctor can prescribe that sometimes can decrease the pain and make the cold sore go away quicker, but it will not cure the cold sore nor prevent it from coming back again in the future.

In summary, the blisters of impetigo tend to be bigger and located around the nose, chin, or anywhere on the body. In contrast, cold sores usually are just located on the lips and around the mouth. In addition, cold sores tend to be painful, whereas impetigo is not. Finally, cold sores tend to recur (come back again in the same place in the future), whereas impetigo usually only happens once in an area.

Henry (Hank) Bernstein, D.O. is a Senior Lecturer in Pediatrics at Harvard Medical School and Professor of Pediatrics at Dartmouth Medical School. Formerly the Associate Chief of General Pediatrics and Director of Primary Care at Children's Hospital Boston, he currently is the Chief of General Academic Pediatrics at Children's Hospital at Dartmouth. He has extensive and varied experience as a primary care pediatrician, and is a spokesperson for the news media on a variety of pediatric health care topics, including vaccination, common childhood illnesses, and practical information for caregivers.

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Harvard Health Publications Source: from the Harvard Health Publications Family Health Guide, Copyright © 2007 by President and Fellows of Harvard College. All rights reserved.

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