Impetigo is a common, highly contagious bacterial skin infection that mainly affects young children. It shows up as clusters of small blisters or red sores that burst and leave behind a distinctive honey-colored crust, most often around the nose, mouth, and on the hands and legs. Globally, about 12% of children have impetigo at any given time, with kids aged 1 to 4 at the highest risk.
What Causes Impetigo
Two types of bacteria are responsible: Staphylococcus aureus (staph) and Streptococcus pyogenes (strep). Staph is by far the more common culprit, causing around 80% of cases on its own. Strep accounts for about 10%, and the remaining 10% involve both bacteria together.
These bacteria live harmlessly on many people’s skin and inside the nose. They cause trouble when they find a way through the skin barrier, often through a cut, scrape, insect bite, or patch of eczema. Once inside, they infect only the most superficial layer of skin, which is why impetigo looks dramatic but rarely causes deep damage. Warm, humid weather and crowded living conditions make transmission easier, and the infection spreads quickly through direct skin-to-skin contact or by sharing towels, bedding, and clothing.
Two Types: Non-Bullous and Bullous
Impetigo comes in two forms that look and behave quite differently.
Non-Bullous Impetigo
This is the classic form, making up about 70% of cases. It starts as tiny fluid-filled bumps or pus-filled spots that quickly merge together and pop. The fluid dries into a thick, golden or honey-colored crust sitting on a red base. These sores typically cluster around the nose, mouth, and on the arms and legs, especially wherever the skin was already broken. New spots can appear nearby within days because touching or scratching a sore transfers bacteria to fresh skin. The nearby lymph nodes may swell slightly, but fever and other body-wide symptoms are rare.
Bullous Impetigo
This form accounts for the other 30% of cases and is caused almost exclusively by staph. Instead of small blisters, it produces larger, fragile, fluid-filled blisters (bullae) that can grow to a noticeable size. The fluid starts clear or yellowish, then turns cloudy or dark. When the blisters burst, they leave behind a thin brown crust with a ring of peeling skin at the edges, but not the honey-colored crust seen in the non-bullous type.
Bullous impetigo tends to show up on the trunk, in skin folds (like the diaper area), and sometimes even inside the mouth. It produces fewer individual sores than the non-bullous form but is more likely to cause fever, diarrhea, or general weakness. Children under two account for 90% of bullous impetigo cases.
How It Spreads
Impetigo is contagious from the moment sores appear until they’ve fully healed or until antibiotic treatment has had time to work. The bacteria spread through direct contact with the sores or with anything the sores have touched, including towels, pillowcases, and clothing. Children often spread it to themselves by scratching one sore and then touching another part of their body, which is why new spots pop up in clusters.
In schools and daycares, outbreaks move fast. Keeping sores loosely covered, washing hands frequently, and not sharing personal items are the most effective ways to slow transmission. Once treatment begins, most children can return to school or daycare after 24 to 48 hours, provided the sores are covered.
How Impetigo Is Diagnosed
Doctors typically diagnose impetigo just by looking at it. The honey-colored crusting of non-bullous impetigo and the large, fragile blisters of the bullous form are distinctive enough that lab tests usually aren’t necessary. A bacterial culture (swabbing the sore and sending it to a lab) may be ordered if the infection keeps coming back, doesn’t respond to initial treatment, or if the doctor suspects a drug-resistant strain of bacteria.
Treatment
Most cases of impetigo are mild and clear up with a prescription antibiotic ointment applied directly to the sores. You typically apply the ointment two to three times a day for about five to seven days. Before applying medication, gently washing the crusted areas with warm water and a soft cloth helps the antibiotic reach the infected skin underneath. Soaking a clean cloth in warm water and holding it against the crusts for a few minutes makes them easier to remove without causing pain.
Oral antibiotics become necessary when the infection is widespread, covers a large area, or hasn’t improved within a day or two of topical treatment. They’re also used when a child has a fever, swollen lymph nodes, a weakened immune system, or is younger than one month old. The oral antibiotics prescribed are chosen to target staph and strep bacteria, and a typical course lasts seven to ten days.
With treatment, sores generally begin to heal within two to three days, and most cases resolve completely within a week to ten days. Without treatment, mild impetigo can sometimes clear on its own in two to three weeks, but the risk of spreading it to others and developing complications is higher.
Possible Complications
Impetigo is usually harmless, but complications can occur when it goes untreated or spreads extensively.
- Ecthyma: A deeper form of infection where the bacteria penetrate below the skin surface, creating painful, thick-crusted sores that can leave scars. This happens when impetigo isn’t treated promptly.
- Post-streptococcal kidney inflammation: In rare cases where strep bacteria are involved, the immune system’s response to the infection can cause inflammation in the kidneys. Signs include dark or reduced urine, swelling in the face or ankles, and high blood pressure. This can develop one to two weeks after the skin infection, even after the sores have healed.
- Cellulitis: The bacteria can occasionally spread to deeper layers of skin and tissue, causing a more serious infection with redness, warmth, swelling, and pain.
Preventing Recurrence
Some children get impetigo repeatedly, especially if they carry staph bacteria inside their nose. Each time they touch their nose and then a scratch or bug bite, they reintroduce the bacteria to broken skin. For recurrent cases, a doctor may prescribe an antibiotic ointment applied inside the nostrils for several days to eliminate the bacterial colony living there. This nasal decolonization can break the cycle of reinfection.
Keeping skin clean and moisturized helps maintain the skin barrier, which is the body’s first defense. Treating underlying conditions like eczema that cause cracks in the skin reduces the number of entry points bacteria can exploit. Trimming children’s fingernails short limits the damage from scratching and reduces the chance of spreading bacteria from one spot to another. Washing bedding, towels, and clothing in hot water during an active infection helps prevent reinfection and household spread.