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