Impetigo and Cellulitis: How to Tell Them Apart and Choose the Right Antibiotic

What’s the difference between impetigo and cellulitis?

You might think both are just "skin infections," but they’re not the same. Impetigo sits on the surface - it’s the red, oozing sores you see on a child’s face or hands, often called "school sores." It’s contagious, messy, and annoying, but rarely dangerous. Cellulitis, on the other hand, digs deeper. It’s a red, swollen, warm patch of skin that hurts to touch, sometimes spreading fast. If left untreated, it can turn into a life-threatening infection.

Both are caused by bacteria - mostly Staphylococcus aureus and Streptococcus - but how they behave is totally different. Impetigo loves broken skin: a scratch from playing, a bug bite, or even eczema flakes. Cellulitis often starts where the skin barrier is weakened - a cut, a fungal infection between the toes, or a surgical scar. And unlike impetigo, cellulitis doesn’t always have a clear border. It just spreads.

How do you know if it’s impetigo?

Impetigo shows up fast. In kids, it usually starts as tiny red bumps around the nose or mouth. Within hours, they turn into blisters that burst and leave a sticky, honey-colored crust. That’s the classic sign. There are two types: nonbullous (70% of cases) and bullous. Nonbullous is the one you’ve probably seen - crusty, not too big, and not deep. Bullous impetigo is rarer. It forms bigger, fluid-filled blisters (2-5 cm wide) that pop easily, leaving a ring-like edge. It’s less itchy, more alarming.

It’s not just kids. Adults get it too, especially if they have diabetes, eczema, or live in hot, humid places like Brisbane. The bacteria can even invade intact skin - no cut needed. That’s why it spreads so fast in daycare centers or sports teams. One kid with impetigo can turn a whole classroom into a hygiene nightmare.

What does cellulitis look like?

Cellulitis doesn’t crust. It swells. The skin becomes tight, shiny, and hot to the touch. It’s usually on the lower legs, but can happen anywhere - face, arms, even around the eyes. The redness doesn’t have a clean edge. It fades into normal skin like a bad watercolor painting. You might feel feverish, tired, or get chills. If the infection spreads under the skin, it can cause pus or fluid leakage. In severe cases, it can lead to sepsis or tissue death.

Unlike impetigo, cellulitis doesn’t just sit there. It grows. If you notice your skin getting redder, harder, or more painful over 12-24 hours, don’t wait. Go to a doctor. Erysipelas is a cousin of cellulitis - it looks similar but has a sharp, raised border and is almost always caused by Streptococcus. It’s more common in older adults and people with lymphedema.

Which antibiotics work for each?

This is where things get messy. There’s no one-size-fits-all answer. It depends on where you live, what bacteria are common there, and whether the infection is mild or severe.

For impetigo, if it’s just a few spots, topical mupirocin ointment works in 90% of cases. You apply it three times a day for 5-7 days. No pills needed. But if it’s widespread, or if the child has a fever, you need oral antibiotics. In the UK and Belgium, flucloxacillin is the go-to. In France, they use amoxicillin-clavulanate or pristinamycin. Why the difference? Because resistance patterns vary. In some areas, more than 30% of Staph aureus strains are MRSA - resistant to flucloxacillin. That’s why doctors in Australia and the US are starting to avoid flucloxacillin as first-line unless they’re sure the strain is sensitive.

For cellulitis, oral antibiotics are almost always needed. The standard is flucloxacillin in the UK, but in the US and Australia, cephalexin or dicloxacillin are more common. In France, amoxicillin is now preferred for mild cases. If MRSA is suspected - think abscess, recent hospital stay, or no improvement after 48 hours - doctors switch to clindamycin or doxycycline. For severe cases with fever, swelling, or diabetes, you’ll likely need IV antibiotics in hospital.

Why does antibiotic choice matter so much?

Every time we use the wrong antibiotic, we help superbugs survive. MRSA is no longer rare. In some Australian hospitals, over 25% of skin infections are caused by MRSA. That means flucloxacillin - once a miracle drug - doesn’t work anymore. Using it when it’s not needed doesn’t just waste money. It makes future infections harder to treat.

Doctors are learning to be smarter. Instead of guessing, they’re starting to culture the infection - swabbing the sore or draining pus - to see exactly what bacteria are there. That’s not always possible in a busy clinic, but it’s becoming more common. If you’ve had cellulitis before, or if your infection didn’t improve after 2 days of antibiotics, ask for a culture. It could save your next treatment.

What about home care and prevention?

Antibiotics help, but they’re not magic. Good hygiene does the rest.

• Wash the infected area daily with soap and water. Pat dry - don’t rub.
• Cover impetigo sores with a light bandage. Change it daily.
• Don’t share towels, clothes, or bedding. Wash them in hot water.
• Keep fingernails short. Scratching spreads the infection.
• Clean cuts immediately with soap and apply an antiseptic.
• If you have eczema, keep it moisturized. Dry, cracked skin is a doorway for bacteria.

For cellulitis, elevate the affected limb. Reduce swelling. Rest. And never ignore a red patch that’s getting worse. The window to stop it from spreading is 48-72 hours. After that, the risk of complications jumps.

When should you see a doctor?

For impetigo: see a doctor if it’s spreading fast, if you have a fever, or if it doesn’t improve after 3 days of mupirocin. Kids should stay home from school until they’ve been on antibiotics for 24 hours.

For cellulitis: go to the emergency room if you have:

• Redness spreading rapidly
• Fever over 38.5°C
• Chills or nausea
• Pain that gets worse instead of better
• Diabetes, heart failure, or a weak immune system

Even if you’re not sure - if something feels off, get it checked. Cellulitis can kill if it reaches the bloodstream.

What’s new in treatment?

Doctors are shifting away from broad-spectrum antibiotics. The goal now is "antibiotic stewardship" - using the right drug, at the right dose, for the right time. New research shows that 7-day courses work just as well as 14-day ones for most cases. Shorter courses mean fewer side effects and less resistance.

Topical treatments are also improving. Mupirocin is still the gold standard for impetigo, but newer options like retapamulin are being tested for MRSA cases. And in some clinics, they’re using rapid DNA tests to identify bacteria in under 2 hours - instead of waiting 2-3 days for culture results.

One big change: more doctors now test for MRSA before prescribing flucloxacillin. If you’re in a high-risk group - recent hospital stay, IV drug use, or living in a crowded home - they’ll skip flucloxacillin and start with something that covers MRSA.

What’s the bottom line?

Impetigo and cellulitis look similar at first glance, but they’re different beasts. One’s a surface problem. The other’s a deep threat. The right antibiotic depends on the infection, your health, and your local bacteria. Don’t assume your last prescription will work again. Don’t wait for symptoms to get worse. And don’t share your antibiotics - even if they "worked before." If you’re a parent, keep an eye on your kids’ scrapes. If you’re older or diabetic, treat every skin break like a potential infection. Early action saves lives - and antibiotics.

Caspian Sterling

Hi, I'm Caspian Sterling, a pharmaceutical expert with a passion for writing about medications and diseases. My goal is to share my extensive knowledge and experience to help others better understand the complex world of pharmaceuticals. By providing accurate and engaging content, I strive to empower people to make informed decisions about their health and well-being. I'm constantly researching and staying up-to-date on the latest advancements in the field, ensuring that my readers receive the most accurate information possible.