What Is Impetigo? Symptoms, Causes and Treatment
Impetigo is a bacterial infection of the superficial layers of the skin, most common in children. Its hallmark is blisters or small erosions that dry into honey-colored crusts, usually around the mouth, nose and face. It is caused by Staphylococcus aureus and Streptococcus pyogenes, and spreads very easily through touch and shared items. It is treated with a topical or oral antibiotic, depending on how widespread the lesions are.
Impetigo is a bacterial skin infection of the superficial layers of the skin and is the most common skin infection in children. The feature people remember is the dry, honey-colored crust (honey-colored crust), usually around the mouth, nose and face. It is very contagious, both at home and at school. The good news is that when it is diagnosed correctly and treatment starts early, it usually clears well without scarring.
Many people assume that any blister or crusted sore is impetigo, but several conditions look similar and are treated differently. In this article, a dermatologist explains what causes impetigo, its types, how to tell it apart from herpes and other conditions, the warning signs that need a doctor, evidence-based treatment, and how to stop it spreading at home.
What causes impetigo?
Impetigo is caused by bacteria on the skin entering the superficial layers through tiny breaks in the skin. The two main bacteria are:
Staphylococcus aureus (staph): the most common cause today, and the cause of the blistering type.
Streptococcus pyogenes (group A strep): can be present together with staph or be the only cause, and is the type linked to kidney complications.
Factors that raise the risk of impetigo include:
Skin that gives bacteria a way in: scrapes, insect bites, scratch marks, eczema (atopic dermatitis) or herpes sores.
Hot, humid weather and heavy sweating: very common in Thailand.
Hygiene and crowded living: for example schools, daycare centers or contact sports teams.
Weakened immunity or diabetes: infection happens more easily and spreads faster.
What types of impetigo are there?
Knowing the type helps show how serious it is and guides the right treatment:
Non-bullous impetigo: the most common type, about 70%. It starts as red bumps or small blisters that break into shallow sores with a honey-colored crust, usually around the nose, mouth and face.
Bullous impetigo: caused by a toxin from staph bacteria, it produces large, thin-walled blisters that break easily and leave a thin crusted edge. It is common in babies and young children, on the trunk, armpits and groin.
Deep type (ecthyma): the infection goes deeper, forming punched-out sores covered by a thick crust with a raised red edge. It may leave a scar after healing, and is seen in people with poor wound care or weakened immunity.
How to tell impetigo apart from similar conditions
This is the important part, because a “blister or crusted sore” that people assume is impetigo may be another condition treated in a completely different way. A doctor tells them apart as follows:
Herpes simplex: clear blisters grouped together on a red base, more burning or stinging than itching, often coming back in the same place. It needs an antiviral, not an antibiotic (the wrong type of medicine will not clear it).
Hand, foot and mouth disease (HFMD): blisters on the palms and soles and sores in the mouth, with fever. It is caused by a virus.
Chickenpox: blisters spread over the body in several stages at the same time, with fever.
Infected eczema: a history of itchy, long-standing rash, then oozing yellow crusts on top. Impetigo often “sets in” on an existing rash.
Fungal skin infection (ringworm): a ring-shaped rash with a raised red edge that is mainly itchy and has no honey-colored crust.
Insect bites that have been scratched into sores: a history of bites and itchy spots, which may become infected and turn into impetigo.
A basic rule of thumb: honey-colored crusts around the mouth or nose of a child that spread quickly and pass to others at home are usually impetigo. But clustered, burning blisters that keep coming back in the same place should make you think of herpes first. If you are not sure, see a doctor for a correct diagnosis.
Warning signs: when to see a doctor quickly
Most impetigo clears up, but see a doctor promptly if you notice any of these signs:
Sores spreading fast, with swollen, red, warm, tender skin around them or fever, which suggests the infection may have gone deeper into cellulitis.
Deep, punched-out sores with thick crusts (ecthyma) or many sores spread over several areas.
Dark urine like the color of water used to rinse meat, puffy eyes, or swelling of the body 1 to 2 weeks after impetigo, which may be post-streptococcal glomerulonephritis (kidney inflammation after a strep infection).
Babies, young children, or people with weakened immunity or diabetes who have impetigo should be watched closely.
No improvement within 3 to 5 days of treatment, or frequent recurrence, which may mean a resistant bacteria (such as MRSA) or a reservoir of bacteria in the nose.
Evidence-based treatment of impetigo
Treatment depends on severity and the number of sores. The evidence-based approach is:
Gently clean the sores: soften and wash off crusts with clean water or saline, and pat dry. Do not pick or scratch, because this spreads the infection and passes it to others.
A few localized sores: use a topical antibiotic such as mupirocin, fusidic acid or ozenoxacin as prescribed. It usually works well in mild cases.
Many sores, wide spread, ecthyma or whole-body symptoms: use an oral antibiotic, chosen by the doctor to cover both staph and strep, and take the full course even when you feel better.
If resistant bacteria (MRSA) are suspected, or treatment is not working: the doctor may take a culture and adjust the medicine, and may also consider clearing bacteria carried in the nose.
Treat the underlying skin condition that lets bacteria in, such as controlling eczema or herpes, to reduce recurrences.
Do not buy steroid creams to put on impetigo yourself, because they do not kill bacteria and may make the infection spread more.
Preventing spread at home and at school
Impetigo spreads through direct contact with the sores and shared items, so prevention matters as much as treatment:
Cover the sores with gauze to reduce contact and to stop scratching around them.
Wash hands often, especially after touching the sores or applying medicine.
Do not share towels, bed linen, clothes or personal items, and wash them separately in hot water.
Keep nails short and stop children picking or scratching, because hands and nails carry bacteria to other places and other people.
Children should stay home from school until the sores no longer ooze, or until at least 24 to 48 hours after starting antibiotics, as advised by the doctor.
Treat scrapes, insect bites and itchy rashes so they heal quickly and give bacteria fewer ways in.
Common myths about impetigo
“It is just internal heat, not contagious” — not true. Impetigo is a bacterial infection that spreads very easily.
“Dusting with powder, or applying toothpaste or aloe vera will dry it faster” — these do not kill bacteria, may irritate the skin, and make the sores harder to care for.
“Squeeze or pick off the crusts so it heals faster” — the more you pick, the more it spreads to other places and other people.
“Once the sore is dry and crusted, it is no longer contagious” — it can still spread until the treatment is finished and the sores have healed. Follow the advice on staying home from school and avoiding contact.
How does impetigo differ in children and adults?
In children, especially ages 2 to 5, it often appears on skin that looked normal before. It starts as small clear blisters around the mouth and nose, which break into honey-colored crusts within a few days. Children usually have no fever and still play as normal. Scratching and then touching other areas is what makes it spread.
In adults, it mostly follows existing skin damage such as eczema that has been scratched into sores, shaving nicks, scrapes or insect bites, so it is common on the legs and on areas that rub. Adults who get it often should be checked for a chronic skin condition or hidden weakened immunity.
How many days does impetigo take to heal, and when can a child return to school?
Once a suitable antibiotic is started, most lesions dry up within 3 to 5 days and heal completely within 7 to 10 days. It usually leaves no scar because the infection stays in the superficial layers of the skin. Some temporary redness or darkening may remain and fades on its own over weeks to months.
As for returning to school, the usual guidance is that a child can go back after at least 24 to 48 hours of antibiotics, or when the sores have dried into crusts and can be covered. If they are still oozing and cannot be fully covered, wait until they dry, because the oozing stage is when it spreads most.
Complications to know about
Spreading deeper into ulcers (ecthyma) — when the infection goes deeper than the outer layer of skin, it becomes a sore with a steep edge and thick crust that heals slowly and leaves a scar.
Cellulitis and lymphangitis — the surrounding skin turns red and swollen and the redness spreads, or a red streak runs up the arm or leg. This needs an oral antibiotic right away.
Staphylococcal scalded skin syndrome — seen in babies and young children, with red skin all over the body that peels off in sheets. It is an emergency.
Post-streptococcal glomerulonephritis — uncommon, appearing about 1 to 3 weeks after the skin infection. Look for urine the color of water used to rinse meat, puffy eyes or high blood pressure. Antibiotics do not prevent this condition, so watching for symptoms is important.
A common misunderstanding: rheumatic fever is linked to strep infection of the throat and does not follow a skin infection.
Frequently asked questions about impetigo
Is impetigo contagious?
Yes, very easily, both through direct contact with the sores and through shared items. The bacteria can also spread from one sore to other parts of your own skin by scratching, so cover the sores, wash your hands and keep personal items separate.
How is impetigo different from herpes?
Impetigo usually has honey-colored crusts around the mouth or nose, spreads quickly and passes to others at home. Herpes causes clear blisters grouped on a red base, with burning or stinging, and often returns in the same place. They are treated with different types of medicine. If you are unsure, have a doctor diagnose it.
Can impetigo clear up on its own? Is an antibiotic always needed?
Some mild cases may improve by themselves, but an antibiotic helps it clear faster, reduces spread and lowers the risk of complications. A few sores are usually treated with a topical medicine, while widespread sores or whole-body symptoms need an oral medicine as prescribed by a doctor.
Will impetigo leave a scar?
The superficial types (non-bullous and bullous) usually heal without scarring if you do not pick at them, but the deeper type (ecthyma) may leave a scar, so it should be treated early.
Does a child with impetigo need to stay home from school?
Yes, until the sores no longer ooze or until at least 24 to 48 hours after starting antibiotics, to reduce the spread to classmates. Cover the sores and make sure the child does not pick or scratch.
What should I do if impetigo keeps coming back?
Frequent recurrence may come from bacteria carried in the nose or from an existing skin condition that lets bacteria in. See a doctor for an assessment. A culture may be needed, along with clearing the carried bacteria and good control of the underlying skin condition.
If you or your child has fast-spreading yellow crusted sores or you suspect impetigo, seeing a doctor early helps you get the right treatment and stop it spreading sooner. Consult a dermatologist at Siam Dermatology, call +66 61 448 7000 or LINE @siamderm.
Written by Dr. Patara Voravutinon, Dermatologist · Last reviewed August 30, 2026
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