Imagine your child comes home from school with red, crusty sores around their nose. Or you wake up with a swollen, hot patch on your leg that’s spreading fast. These aren’t just rashes-they’re bacterial skin infections, and they’re more common than most people think. In the UK alone, impetigo and cellulitis make up a huge chunk of GP visits, especially in kids and older adults. The good news? They’re treatable. The bad news? Getting the diagnosis and treatment right matters more than ever because antibiotics aren’t working like they used to.
What’s the Difference Between Impetigo and Cellulitis?
Impetigo and cellulitis look similar at first glance-red, inflamed skin-but they’re totally different in how deep they go and how they spread.
Impetigo stays on the surface. It’s a shallow infection of the top layer of skin, the epidermis. You’ll usually see it on the face-especially around the nose and mouth. It starts as tiny blisters or pimples, then turns into oozing sores that form that unmistakable honey-colored crust. Kids between 2 and 5 are most at risk, and it spreads like wildfire in nurseries and schools. About 70% of cases are the non-bullous type. The other 30% are bullous impetigo, which affects babies under 2 and causes larger, fluid-filled blisters that burst easily.
Cellulitis, on the other hand, digs deeper. It hits the dermis and the fatty tissue underneath. You won’t see a crust. Instead, you’ll notice a red, swollen, warm patch of skin that doesn’t have clear edges. It often shows up on the lower legs in adults, and it can spread quickly. Unlike impetigo, cellulitis isn’t contagious. It happens when bacteria sneak in through a cut, scrape, insect bite, or even a crack in the skin from athlete’s foot.
One key difference: impetigo is mostly caused by Staphylococcus aureus, sometimes mixed with Streptococcus pyogenes. Cellulitis? Usually Streptococcus pyogenes, with Staphylococcus aureus as a common second player. This matters because it changes what antibiotics work.
Why Penicillin Doesn’t Work Anymore
For decades, penicillin was the go-to for skin infections. But that’s history now. Around 85% of Staphylococcus aureus strains in the US and UK produce an enzyme called penicillinase that breaks down penicillin before it can kill the bacteria. That means if you’re still prescribing penicillin for impetigo, you’re probably wasting time-and letting the infection get worse.
Studies from the 1990s showed penicillin failed in about 68% of cases. Today, it’s even worse. In some areas, over half of community-acquired Staphylococcus aureus infections are now methicillin-resistant (MRSA). That’s not just a buzzword-it means drugs like flucloxacillin and cephalexin, which used to be reliable, might not work either.
That’s why doctors now start with antibiotics that actually kill these bugs. For impetigo, topical mupirocin (Bactroban) is the first-line treatment. It’s applied three times a day for five days. It works on 90% of cases if the infection is mild and limited. For more widespread or bullous impetigo, oral antibiotics like cephalexin or dicloxacillin are used. But if MRSA is suspected, doxycycline or trimethoprim-sulfamethoxazole are better choices.
How Antibiotics Are Chosen Today
There’s no one-size-fits-all anymore. Treatment depends on three things: how bad the infection is, where it is, and what bugs are likely causing it.
For impetigo:
- Mild, localized: Topical mupirocin. Clean the area with warm soapy water first, gently remove crusts, then apply the ointment.
- Widespread or bullous: Oral antibiotics like cephalexin (25-50 mg/kg/day in two doses) for 7 days.
- MRSA suspected: Doxycycline (100 mg twice daily) or trimethoprim-sulfamethoxazole (160/800 mg twice daily) for 7-10 days.
For cellulitis:
- Mild: Oral cephalexin or dicloxacillin, 500 mg four times a day for 5-14 days.
- Severe (fever, swelling, spreading fast): Hospital admission, IV antibiotics like cefazolin (1-2 g every 8 hours).
- MRSA suspected: Add doxycycline or trimethoprim-sulfamethoxazole to the regimen.
There’s also a new option: topical retapamulin (Altabax). A 2024 study showed it cured 94% of impetigo cases in kids-making it a strong alternative if mupirocin isn’t available or if resistance is a concern.
When It Gets Dangerous
Most cases of impetigo clear up without trouble. But it can lead to something serious: post-streptococcal acute glomerulonephritis. That’s a kidney problem that can happen after a strep infection-even if the skin sore looks gone. It’s rare (1-5% of cases), but it’s why doctors still check urine in kids with strep-related impetigo.
Cellulitis? It’s far more dangerous. About 5-9% of cases lead to bacteria entering the bloodstream (bacteremia). In 0.3% of cases, it turns into necrotizing fasciitis-the flesh-eating infection you hear about in the news. And in 2-4% of hospitalized patients, it leads to sepsis.
There’s also Staphylococcal Scalded Skin Syndrome (SSSS). It’s rare, mostly in babies under 2, and it’s terrifying. The skin turns red, then peels off like a burn. It’s not an infection of the skin itself-it’s a toxin from Staphylococcus aureus that attacks the skin’s glue. If your child has a high fever and skin that looks like it’s been scalded, call emergency services immediately. Mortality is low with prompt treatment, but delay can be fatal.
What You Can Do to Prevent It
Prevention is easier than you think.
- Wash hands often, especially after touching sores or changing bandages.
- Keep cuts, scrapes, and insect bites clean. Use antiseptic cream and cover them.
- Don’t share towels, clothing, or bedding if someone in the house has impetigo.
- Treat athlete’s foot-it’s a common gateway for cellulitis.
- If your child has impetigo, keep them home from school or nursery until 24 hours after starting antibiotics, or until the sores are dry and crusted.
During outbreaks in schools or care homes, daily washing with antibacterial soap can cut transmission by up to 50%. That’s not just advice-it’s backed by data.
Why Diagnosis Matters More Than Ever
Doctors don’t always need a lab test. Impetigo is usually diagnosed by sight-the honey crust is unmistakable. Cellulitis? It’s also mostly clinical. But the tricky part is ruling out mimics: deep vein thrombosis, gout, or even allergic reactions can look like cellulitis.
That’s why antibiotics shouldn’t be handed out like candy. If you’ve had cellulitis before and it came back, or if it’s not improving after 48 hours, you need a culture. Same with impetigo that doesn’t respond to mupirocin. Resistance is rising, and we’re running out of options.
That’s why new tools are coming. The NIH is funding research into point-of-care tests that can identify the exact bacteria and its resistance profile in under 30 minutes. Imagine walking into a clinic, getting a quick swab, and walking out with a targeted antibiotic-not a guess.
What to Watch After Treatment
Even after the redness fades, keep an eye out.
- For impetigo: Watch for new sores or signs of kidney problems-swelling in the face or ankles, dark urine, or high blood pressure.
- For cellulitis: If the redness spreads again, you develop a fever, or the pain gets worse, go back. That’s not a relapse-it’s a warning.
Most people recover fully. But if you’re over 65, diabetic, or have poor circulation, you’re at higher risk for recurrence. That’s why ongoing skin care matters. Moisturize dry skin, manage diabetes tightly, and treat fungal infections fast.
Is impetigo contagious?
Yes, impetigo is highly contagious. It spreads through direct skin contact or by touching things like towels, toys, or bedding that have been contaminated. Children in nurseries and schools are most at risk. Once antibiotics are started, they’re no longer contagious after 24 hours.
Can cellulitis spread from person to person?
No, cellulitis is not contagious. It happens when bacteria from your own skin or a minor injury get into deeper layers. You can’t catch it from someone else, even if you touch their infected area.
Why do antibiotics sometimes not work?
Many strains of Staphylococcus aureus now produce enzymes that destroy common antibiotics like penicillin. Over half of community cases in the UK and US are now MRSA, meaning they’re resistant to drugs like flucloxacillin. That’s why doctors now use alternatives like doxycycline or trimethoprim-sulfamethoxazole for suspected resistant cases.
How long does it take for impetigo to clear up?
With proper treatment, impetigo usually improves within 3 days and clears completely in 7-10 days. Without treatment, it can last weeks and may leave temporary skin discoloration. Crusting usually dries up in 48-72 hours.
When should I go to the hospital for a skin infection?
Go to the emergency room if you have a high fever, rapid spreading redness, severe pain, blisters or peeling skin, or if you feel dizzy, confused, or short of breath. These could be signs of sepsis, necrotizing fasciitis, or Staphylococcal Scalded Skin Syndrome-all medical emergencies.
Are there any new treatments for impetigo?
Yes. Topical retapamulin (Altabax) has shown 94% effectiveness in recent trials and is now an approved alternative to mupirocin, especially where resistance is a problem. It’s safe for children over 2 months and applied twice daily for 5 days.
What Comes Next?
The fight against bacterial skin infections is shifting. We’re moving away from broad-spectrum antibiotics and toward smarter, targeted care. That means better diagnostics, better stewardship, and better outcomes.
For now, the rules are simple: treat early, choose the right antibiotic, and don’t ignore the signs. If you’re unsure, see your GP. A small skin sore today could be a major problem tomorrow-if it’s not handled right.