When Impetigo Needs Urgent Review: Fever, Spreading Redness and Sores That Are Not Healing

It started as two honey-colored crusts under a five-year-old’s nose, the kind every preschool teacher recognizes on sight. The cream went on twice a day. Eight days later the crusts are still there, a new patch has appeared on the chin, and this morning the child felt hot to the touch and refused breakfast. The parent stands in the bathroom holding a half-used tube and asks the question nobody answered at the first visit: what does impetigo not healing actually mean?

Most of the time, impetigo is a nuisance rather than a threat. The skin clears, the crusts fall away, and there is usually no scar. But a small number of cases behave differently, and the difference is not always obvious from across a room.

This article is about that difference: how to tell slow from stuck, what fever and spreading redness signal, and which signs mean the treating team should hear from you today.

Impetigo not healing: why 'slow' and 'stuck' are two different problems

Impetigo is a contagious surface infection of the skin, usually caused by Staphylococcus aureus or group A Streptococcus bacteria. With appropriate treatment, the NHS describes it as generally clearing within seven to ten days. That range matters, because a sore that looks unchanged on day three is not the same as a sore that looks unchanged on day ten.

Slow healing usually looks like this: the crusts are drying, no new spots have appeared for a couple of days, the surrounding skin is calm, and the person feels well. The infection is losing. It simply has not finished losing yet.

Stuck healing looks different. New sores keep appearing while the old ones persist. The redness at the edge of a patch creeps outward instead of fading. Crusts that were dry become wet again. The skin around a sore feels warm, tight or tender, or the person develops a fever, chills or a general sense of being unwell. Any of these suggests that either the treatment is not reaching the bacteria, the bacteria are not susceptible to it, the infection has gone deeper than the top layer of skin, or the diagnosis was never impetigo in the first place.

The practical question is not “how many days has it been” but “which direction is it moving.” A clinician can usually settle that in a few minutes of looking and asking, which is why a same-day call is reasonable whenever the trajectory is wrong. Waiting for a course to “finish” before reporting that it is failing gives a deeper infection time to establish itself.

What actually happens in impetigo: how bacteria get under the skin's surface

Healthy skin is a remarkably good barrier. Impetigo begins when that barrier is breached, even microscopically. A scratch from eczema, an insect bite, a cold sore, a scraped knee, or the raw skin under a runny nose gives bacteria that normally sit harmlessly on the surface a way into the outermost layer, the epidermis. Mayo Clinic notes that the bacteria can also enter skin that looks intact, though minor breaks are the usual route.

Once inside, the bacteria multiply in the shallow layers just beneath the surface. Two patterns follow. In non-bullous impetigo, the most common form, tiny blisters break quickly and the fluid dries into the characteristic honey-colored crust. In bullous impetigo, a toxin produced by certain Staphylococcus aureus strains splits the skin layers apart, producing larger, fragile, fluid-filled blisters that leave a thin rim of skin when they burst. Cleveland Clinic describes bullous impetigo as more often affecting the trunk, arms and legs, while non-bullous impetigo favors the face.

Because the infection sits so close to the surface, it spreads easily. Fingers that scratch one sore carry bacteria to the next patch of skin, which is why sores tend to appear in clusters and travel across a face or down an arm. Towels, bedding and toys do the same job between people.

Understanding this mechanism explains both the reassuring and the worrying versions of the illness. As long as the infection stays in the epidermis, it tends to respond to treatment and heal without scarring, because the deeper skin layers that produce scar tissue are untouched. When bacteria reach those deeper layers, the character of the illness changes, and so does the urgency.

How long can you leave impetigo untreated, and what does normal recovery look like?

People ask this in two very different frames of mind. Some are hoping to avoid a medical visit. Others have already waited and are wondering whether they have done harm. The honest answer sits between them.

Left alone, impetigo often does resolve. The NHS states that without treatment it usually clears within two to three weeks, and Mayo Clinic notes that mild cases in otherwise healthy people may improve on their own. Guidelines still generally favor treatment, for three reasons: it shortens the illness, it shortens the period during which the person can infect others, and it lowers the small risk of complications. The NHS advises that people remain contagious until the sores have dried and crusted over or until 48 hours after treatment begins, so an untreated case keeps a child out of school or nursery for considerably longer.

Once treatment starts, the typical course runs roughly like this. Within the first two to three days, new sores should stop appearing and existing crusts should begin to dry and lift. By the end of the first week, most patches are flat, pink and smooth rather than crusted. The pink fades over the following weeks. The CDC and NHS both note that the sores usually heal without scarring, though darker or lighter marks can linger for a while, especially on deeper skin tones.

The moments to pay attention to are the ones where this sequence stalls. If day three arrives with fresh sores, or day seven arrives with crusts that are still wet and spreading, the illness has stepped off the expected path. That is the point to call rather than to add another week of hoping.

Impetigo spreading fast: what a rapidly widening patch usually means

Some spread is expected in the first day or two, before treatment has had time to work. Rapid spread after that, particularly if redness is advancing across skin that has no sores on it, is a different signal.

Three explanations are common. The first is simple mechanical spread: scratching, picking, or a shared towel moving bacteria to new skin. This produces new crusted sores in new places, not smooth expanding redness, and it usually settles once the sores are covered and hand-washing tightens up. The second is a mismatch between the treatment and the bacteria, discussed in the next section. The third, and the one that changes urgency, is that the infection has moved from the epidermis into the deeper layers, producing cellulitis.

Cellulitis is an infection of the deeper skin and the tissue just beneath it. The NHS describes it as skin that becomes red, hot, swollen and painful, sometimes with blistering, and it can be accompanied by fever, chills and feeling generally unwell. On darker skin the redness may be harder to see, so warmth, swelling and tenderness carry more weight. Unlike impetigo, which stays superficial and mostly itches, cellulitis spreads beneath the surface, hurts, and does not respond to creams because the cream cannot reach it.

A useful home test is the outline. Draw gently around the edge of the red area with a washable marker and check it a few hours later. Redness that has clearly moved beyond the line, a red streak tracking away from the sore toward the body, or swelling that makes the skin feel tight are all reasons for same-day assessment. None of this is meant to alarm; it is meant to give a clear threshold so that a worried parent is not left guessing.

Impetigo antibiotics not working: why isn't the cream doing its job?

“Why isn’t mupirocin working?” is one of the most searched questions about this condition, and the answer is rarely that the person is doing something wrong. Mupirocin is a topical antibiotic, a medicine applied directly to the skin that stops bacteria from making the proteins they need to grow. It is a common first-line choice for small, localized patches, and several factors can blunt it.

Crust is the first. Antibiotic cream applied on top of a thick, dry crust sits on dead material and never meets the bacteria underneath. Guidelines and patient resources, including the NHS, advise gently soaking or washing away loose crusts with warm water before applying treatment. A cream that has been going onto crust for a week has effectively not been used.

Extent is the second. Topical treatment is intended for a few small sores. When impetigo covers a large area, involves several body regions, or is the bullous form, oral antibiotics are generally recommended instead, because cream cannot be applied reliably everywhere. Mayo Clinic describes this distinction explicitly.

Resistance is the third. Some Staphylococcus aureus strains are methicillin-resistant, known as MRSA, and some are resistant to mupirocin itself. Resistance means the bacteria have changed in ways that let them survive a medicine that would ordinarily kill them. When a clinician suspects this, a swab of the sore can be sent to the laboratory to identify the organism and test which antibiotics it responds to. That result guides the next choice.

Misdiagnosis is the fourth. A patch that was never bacterial will not improve with any antibiotic. Whatever the cause, the decision to swab, switch or stop belongs to the prescribing clinician. Stopping early on one’s own tends to leave surviving bacteria, and switching without guidance tends to waste more time.

Fever with impetigo: when the infection has moved deeper

Uncomplicated impetigo does not usually cause fever. The infection is confined to the surface, the immune system handles it locally, and the person feels fine apart from the itch. A fever, particularly one that appears after several days of treatment, tells you the body is now responding to something larger than a few surface sores.

The most common explanation is cellulitis, described above. A less common but more serious one is ecthyma, a deeper form of impetigo in which the infection punches through the epidermis into the dermis, producing painful sores that turn into ulcers with a thick gray-yellow crust and a raised, purple-red border. MedlinePlus lists ecthyma among the complications of untreated impetigo. Because ecthyma involves the layer of skin that produces scar tissue, it is one of the few forms that can leave permanent marks.

Rarely, group A streptococcal skin infection can be followed by post-streptococcal glomerulonephritis, an inflammation of the kidney’s filtering units. The CDC notes this as an uncommon complication that can occur one to three weeks after the skin infection. Its signs include dark or cola-colored urine, swelling around the eyes or in the legs, and reduced urine output. It is worth knowing about not because it is likely, but because it can appear after the skin has already healed, when nobody is still thinking about impetigo. The CDC also notes that, unlike strep throat, strep skin infections are not thought to trigger rheumatic fever.

Any fever accompanying impetigo warrants a same-day call. In an infant, an older adult, or anyone with a weakened immune system, that call becomes more pressing still, because these groups can deteriorate faster and show fewer of the classic signs.

Who is usually treated straight away, and who is usually asked to wait and watch

Guidelines separate impetigo cases by how many sores there are, where they are, how the person is otherwise, and whether earlier treatment has failed. This is what typically shapes the plan, though every decision sits with the treating clinician who has seen the skin.

People commonly treated with topical measures alone include those with a small number of sores in one area, no fever, no signs of deeper infection, and no underlying condition that weakens immunity. The NHS notes that, in the United Kingdom, an antiseptic cream is often tried first for localized non-bullous impetigo, with a topical antibiotic reserved for cases that do not respond. In the United States, a topical antibiotic is more often the initial choice, as Mayo Clinic describes. Neither approach is a recommendation here; both reflect how guidelines weigh the benefit of treatment against the wider goal of limiting antibiotic resistance.

People more often started on oral antibiotics from the outset include those with widespread sores, bullous impetigo, sores near the eyes or on the scalp where cream is hard to apply, signs of cellulitis or fever, or a failed course of topical treatment. Infants, people with eczema covering large areas, people with diabetes, and those with weakened immune systems are also assessed more cautiously, because their skin barrier or defenses are already compromised.

“Wait and watch” is a legitimate plan for a well person with a couple of small crusts, provided it comes with a clear threshold for re-contact. It stops being the right plan the moment new sores appear, the area spreads, or the person becomes unwell. The value of a first visit is often less the prescription than the agreed point at which to come back.

Reassuring signs versus red flags: a side-by-side guide

Parents and patients often say the hardest part is not the treatment but the uncertainty about whether what they are seeing is normal. The table below sets typical, expected features alongside the ones that call for prompt review. It is a guide to when to ask, not a tool for diagnosing yourself.

Feature	Usually expected	Prompt review advised
Number of sores	Stops increasing within 2–3 days of treatment	New sores appearing after day 3, or many appearing daily
Crusts	Drying, lifting, leaving smooth pink skin	Staying wet, thickening, or turning into ulcers
Surrounding skin	Mild pinkness at the edge that fades	Spreading redness, warmth, swelling, tightness or a red streak
Pain	Itching, mild soreness	Increasing pain, tenderness to light touch
General health	Feels well, eating and sleeping normally	Fever, chills, drowsiness, vomiting, refusing fluids
Timeline	Clear improvement by 7–10 days (NHS)	No improvement after a week of correct use, or recurrence soon after finishing
Urine	Normal	Dark, cola-colored or reduced urine in the weeks after infection

Two notes on reading it. First, one entry in the right-hand column is enough to justify a call; you do not need several. Second, the left-hand column describes the average course reported by the NHS and Mayo Clinic, not a guarantee. Some healthy children take the full ten days to clear and are fine. Some develop a fever on day four and need a different plan. The table is there to make the conversation with your clinician quicker and more specific.

Can impetigo still spread while on antibiotics, and how long is impetigo contagious?

Yes, impetigo can spread during the first day or two of treatment. Antibiotics need time to reduce the bacterial load on the skin, and a sore that is still weeping is still shedding bacteria. This is why guidance focuses on a window rather than a moment.

The NHS states that a person is no longer considered contagious 48 hours after starting treatment, or once all the sores have dried and crusted over, whichever comes first. The CDC gives the same 24-to-48-hour frame for group A strep skin infections once antibiotics begin. Schools and childcare settings commonly use this threshold, so a child started on treatment on Monday morning is usually able to return on Wednesday if the sores are crusted or covered.

Spread during that window happens mainly by touch: hands that scratch a sore then touch another person, a shared towel, a pillowcase, a toy passed between siblings. Covering sores with a light dressing where practical, keeping fingernails short, washing hands after applying cream, and using separate towels and washcloths all interrupt this. Washing bedding, towels and clothing that touched the sores at a normal hot cycle is enough; special disinfection is not needed.

The question hides a second worry that people rarely say out loud: “If it is still spreading on day two, is the treatment failing?” Usually not. Spread that stops by day three is the expected pattern. Spread that continues past day three, or redness that advances under intact skin rather than as new crusted spots, is the pattern that warrants a call. The clock, in other words, only starts once the medicine is being used correctly, on crust-free skin, at the frequency the prescriber set.

Impetigo not healing in a child: eczema, cold sores and other look-alikes

Sometimes the reason impetigo will not heal is that it is not impetigo, or not only impetigo. Several common skin problems mimic it or sit underneath it, and each changes the plan.

Eczema is the most frequent partner. Children with atopic dermatitis have a weakened skin barrier and often carry Staphylococcus aureus on their skin even when it looks calm. Impetigo on top of eczema tends to recur, because clearing the bacteria without settling the eczema simply reopens the door. Clinicians often treat both at once, and a parent who reports “it keeps coming back in the same creases” is giving a valuable clue.

Cold sores, caused by the herpes simplex virus, produce clusters of small blisters around the lips that crust over and can look strikingly similar. They are not bacterial, so an antibiotic does nothing for them, though they can become secondarily infected with bacteria. A history of tingling before the blisters appear, or recurrence in exactly the same spot, points toward a viral cause.

Scabies, an infestation with a tiny mite that burrows into the skin, causes intense night-time itching and often becomes infected from scratching. Treating the infection without treating the mite leaves the itch, and the cycle continues. Ringworm, a fungal infection, forms a ring with a clearer center and does not weep. Contact dermatitis from a soap or fabric can crust when scratched.

None of these can be reliably told apart from a photograph or a description, which is why persistent or recurring sores deserve a hands-on look and, if needed, a swab. The point for a parent is simple: “it should have gone by now” is itself useful information for the clinician, because it widens the list of things worth considering.

How to make sure impetigo doesn't come back

Recurrence is frustrating and common enough that it deserves its own plan. The bacteria involved live on skin and in the nose of a substantial share of healthy people, a state called colonization, meaning the organism is present without causing illness. Impetigo returns when colonized skin meets a fresh break in the barrier.

Protect the barrier first. Keep eczema well controlled with the regimen your clinician has set, moisturize dry skin, treat insect bites and scrapes promptly with soap and water, and keep fingernails short so scratching does less damage. A runny nose in a young child softens the skin under the nostrils and is a classic starting point, so gentle wiping and a thin barrier ointment there can help.

Reduce the bacterial load second. Mayo Clinic and the NHS both emphasize regular hand-washing, individual towels and washcloths, and washing bedding and clothing that touched sores. Do not share razors, and clean shared sports equipment. Where impetigo keeps returning within a household, a clinician may consider swabbing family members’ noses to find who is carrying the organism, and may discuss a short decolonization treatment. That is a clinical decision made case by case; it is not something to attempt with leftover cream.

Finish the course third. Sores can look healed while bacteria persist at the edges. Stopping treatment early because the skin looks fine is one of the most common routes to a return a week later.

Recurrence despite all of this is a reason to go back, not to repeat the same treatment. Repeated impetigo can point to persistent carriage, an undiagnosed skin condition, or a resistant organism, and each has its own answer.

What people often get wrong about impetigo that is not healing

“Impetigo means poor hygiene.” It does not. The bacteria responsible live on the skin of many healthy people. Impetigo follows a break in the skin, and children get more breaks in the skin than anyone. The CDC and NHS both describe it as most common in young children for exactly this reason, not because of how often they are bathed.

“If it’s still spreading, the antibiotic has failed.” Only after the first two to three days. Some spread in that window is expected while the bacterial load falls. Spread that continues after day three, or fever at any point, is the signal to call.

“The crust protects the sore, so leave it alone.” The crust is dried fluid and dead material. It shelters bacteria from topical treatment and makes the sore look worse than it is. Gently soaking off loose crust with warm water before applying medicine is standard advice. Picking or scrubbing, on the other hand, spreads bacteria and damages skin.

“It will scar.” Ordinary impetigo stays in the epidermis and typically heals without a scar, according to both the CDC and Mayo Clinic. Temporary color change is common, especially on deeper skin tones, and fades over weeks to months. Scarring is mainly a risk with ecthyma, the deeper form, and with aggressive picking.

“Antiseptic or antibiotic cream from the cabinet will do.” Leftover products of unknown age, applied on top of crust, are a frequent reason people believe treatment has “already failed” before a clinician has assessed the sores. Impetigo that has not improved after a week of correct use of a prescribed treatment is the meaningful threshold, and it deserves a fresh look rather than a fresh guess.

Questions to ask your care team when impetigo is not improving

A short, specific list turns a rushed appointment into a useful one. These are the questions that tend to change what happens next.

• Is this still impetigo, or could something else be going on underneath, such as eczema, a cold sore or scabies?
• Should a swab be sent to identify the bacteria and check which antibiotics it responds to?
• Am I applying the treatment correctly? Should crusts be soaked off first, and how often should it go on?
• Is the infection still confined to the surface, or are there signs it has gone deeper?
• If this treatment is switched, what improvement should I expect to see, and by when?
• When exactly can my child return to school or childcare?
• Are there signs over the next few weeks, such as changes in urine or swelling, that I should watch for even after the skin has healed?
• Should other people in the household be checked or treated?
• What is the single sign that means I should call you today rather than wait for the next appointment?

Write down the answers, particularly the timeline. “Come back if it isn’t better” is far less useful than “if no new sores by Thursday and crusts drying by Saturday, you’re on track; if not, call.” Ask for that level of detail. Most clinicians are glad to give it, and it is the clearest protection against both over-worrying and under-reacting.

If the treating clinician recommends a swab, a change of medicine, or a period of watching, that decision rests with them, informed by what they can see and what you report. Your job is to report accurately and early.

When to call your doctor: red flags with impetigo

Most impetigo never reaches this section. When it does, the signs below are the ones that guidelines and patient resources from the NHS, CDC and Mayo Clinic consistently flag. One is enough.

Call the same day if:

• There is a fever, chills, or the person seems unusually drowsy, irritable or unwell.
• Redness, warmth or swelling is spreading beyond the sores, especially across skin without crusts, or a red streak is tracking away from the area.
• The area is increasingly painful or tender to light touch.
• Sores are turning into deeper ulcers with thick gray or purplish crusts.
• New sores are still appearing after three days of correct treatment, or there is no clear improvement after a week.
• Sores are near the eye, or the eye becomes red, swollen or sticky.
• The person is an infant, has a weakened immune system, or has diabetes.
• Urine becomes dark or cola-colored, or there is new swelling around the eyes or in the legs, at any point in the weeks after the infection.

Seek emergency care immediately if: the person is very hard to wake, is breathing fast or struggling to breathe, has a rash that does not fade when a glass is pressed against it, has cold, blotchy or mottled skin, is confused, or is a baby who is floppy, not feeding, or has not passed urine for many hours. The NHS lists these among the signs of sepsis, the body’s overwhelming response to infection, which is rare after impetigo but requires urgent hospital treatment.

In every case, the decision about swabs, medicines, referral or observation belongs to the treating team. Your part is recognizing the signs and making the call early, which is exactly what this article has tried to make easier.

Frequently asked questions

Why isn't mupirocin working for my impetigo?

The most common reasons are crust blocking the cream from reaching bacteria, sores too widespread for a topical treatment, a resistant strain of Staphylococcus aureus, or a diagnosis that was never bacterial. Gently soaking off loose crusts before applying is standard advice. If there is no clear improvement after about a week, ask your clinician whether a swab or a different approach is needed rather than continuing unchanged.

How long can you leave impetigo untreated?

Mild impetigo in a healthy person often clears on its own within two to three weeks, according to the NHS. Guidelines still generally favor treatment because it shortens the illness, cuts the contagious period to about 48 hours, and lowers the small risk of deeper infection or kidney complications. Any fever, spreading redness or worsening sores means the watch-and-wait window has closed.

Can impetigo still spread while on antibiotics?

Yes, during roughly the first 48 hours. Antibiotics need time to reduce the bacterial load, and weeping sores still shed bacteria. Both the NHS and CDC consider a person no longer contagious 24 to 48 hours after treatment starts or once all sores have crusted. Covering sores, hand-washing after applying cream, and using separate towels limit spread in that window.

How do I make sure impetigo doesn't come back?

Finish the full course even when the skin looks clear, keep eczema and dry skin well managed, treat scrapes and bites promptly, keep nails short, and avoid sharing towels, washcloths or razors. If it keeps returning within a household, a clinician may consider checking for nasal carriage of the bacteria. Repeated recurrence is a reason to go back rather than to reuse leftover cream.

What does impetigo getting worse look like?

Worsening impetigo shows new sores appearing after the first three days of treatment, crusts that stay wet or thicken, redness that spreads across skin without sores, warmth or swelling around the patches, increasing pain, or a fever. Any of these signs suggests the treatment is not working, the infection has gone deeper, or the diagnosis needs revisiting, and deserves a same-day call.

Is fever normal with impetigo?

No. Uncomplicated impetigo stays in the surface layer of skin and does not usually cause fever. A fever suggests the infection has spread deeper, most often as cellulitis, or that the body is responding to a larger problem. Fever alongside impetigo is a reason to contact a clinician the same day, particularly in infants, older adults, or anyone with a weakened immune system.

Will impetigo leave scars?

Usually not. Because ordinary impetigo affects only the epidermis, the CDC and Mayo Clinic both note it typically heals without scarring. Temporary darker or lighter patches are common and fade over weeks to months. Scarring is mainly a risk with ecthyma, the deeper ulcerating form, or when sores are picked or scrubbed, which damages the layers that produce scar tissue.

Can impetigo spread to the kidneys?

Not directly, but group A streptococcal skin infection can rarely be followed by post-streptococcal glomerulonephritis, an inflammation of the kidney’s filtering units. The CDC describes it as uncommon and typically appearing one to three weeks after the skin infection. Dark or cola-colored urine, reduced urine, or swelling around the eyes or legs should be reported promptly, even if the skin has already healed.

When can my child go back to school with impetigo?

Most guidance, including the NHS, allows return 48 hours after starting treatment or once all sores have dried and crusted over, whichever is sooner. Sores that are still moist should be covered with a light dressing where practical. Individual schools and childcare settings may have their own policies, so it is worth confirming with them and with your clinician.

Should the crusts be removed before applying treatment?

Loose crusts are usually softened and gently removed with warm water and mild soap before medicine goes on, because cream applied over dry crust cannot reach the bacteria underneath. The NHS includes this in its self-care advice. Never pick, scratch or scrub at the sores, as that spreads bacteria and can push the infection deeper. Follow the specific instructions your prescriber gave you.

References

• NHS: Impetigo
• CDC: About Impetigo
• MedlinePlus: Impetigo
• Cleveland Clinic: Impetigo

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.