Bacterial Skin Infections: Impetigo, Cellulitis, and Antibiotics Explained

When your child comes home from school with red, crusty sores around the nose, or you wake up with a swollen, hot patch of skin on your leg, it’s easy to assume it’s just a minor rash. But these could be signs of bacterial skin infections - specifically impetigo or cellulitis. These aren’t just annoying rashes. They’re infections that spread fast, need the right antibiotics, and can turn dangerous if ignored.

What Is Impetigo, and Why Is It So Common in Kids?

Impetigo is the most common bacterial skin infection in children under 5. You’ll see it in daycare centers, schools, and playgrounds. It starts as tiny red bumps or blisters that quickly turn into oozing sores. Within a few days, they form a thick, honey-colored crust - which is why doctors call it "school sores."

It’s not just ugly - it’s contagious. One kid with impetigo can spread it to others through shared towels, toys, or even a quick hug. About 70% of cases are the nonbullous type, meaning small sores that crust over. The other 30% are bullous - larger, fluid-filled blisters that burst easily, leaving raw patches behind. These are more common in babies under 2.

The bacteria behind it? Not what you might think. For decades, people blamed Group A Strep. But today, Staphylococcus aureus is the main culprit in 80-90% of cases, often mixed with Streptococcus pyogenes. And here’s the catch: nearly all these staph strains make an enzyme called penicillinase that breaks down penicillin. That means if your doctor prescribes penicillin, it’s likely to fail - about 68% of the time.

How Cellulitis Is Different - and Much More Serious

While impetigo stays on the surface, cellulitis digs deep. It attacks the dermis and fatty tissue under the skin. You’ll notice a red, swollen, warm, painful area that spreads quickly. The edges are blurry, not sharp. It often shows up on the lower legs in adults, but can hit any part of the body.

Cellulitis doesn’t spread from person to person. It starts when bacteria - usually Streptococcus pyogenes or Staphylococcus aureus - get in through a cut, scrape, insect bite, or even a crack in the skin from athlete’s foot. About 65% of cases come from minor injuries you might not even remember.

This isn’t a rash you can wait out. If left untreated, it can lead to sepsis, abscesses, or worse - necrotizing fasciitis, the "flesh-eating" infection. Around 5-9% of people with cellulitis develop bacteremia (bacteria in the blood), and 2-4% of hospitalized patients die from complications. The risk spikes with age, diabetes, obesity, or poor circulation. People over 65 are 24.6 times more likely to get it per 1,000 people each year.

Antibiotics: What Works, What Doesn’t, and Why

Getting the right antibiotic isn’t just about killing bacteria - it’s about matching the bug, the location, and the resistance patterns.

For mild, localized impetigo, topical treatment works best. Mupirocin (Bactroban) is applied three times a day for 5 days. Studies show a 92% cure rate. You clean the area with warm soapy water first, then gently remove the crusts before applying. Most kids start improving in under 3 days and stop being contagious after 24 hours.

But if the infection is widespread, involves the face, or is bullous, you need oral antibiotics. Cephalexin (Keflex) or dicloxacillin are standard. Dosing is based on weight in kids - usually 25-50 mg/kg per day split into 4 doses. Treatment lasts 7 days.

For cellulitis, topical antibiotics won’t cut it. You need drugs that reach deep into tissue. For mild cases, oral cephalexin or dicloxacillin (500 mg four times daily) for 5-14 days is common. But if the infection is spreading fast, you have a fever, or you’re immunocompromised, you’ll need IV antibiotics like cefazolin in the hospital.

Here’s the big shift in 2025: MRSA - methicillin-resistant Staphylococcus aureus - is now behind half of community skin infections in the U.S. That means traditional antibiotics like penicillin, amoxicillin, and even some cephalosporins won’t work. The Infectious Diseases Society of America now recommends doxycycline or trimethoprim-sulfamethoxazole (Bactrim) as first-line for suspected MRSA. These have 85-90% success rates in 7-10 days.

New Treatments and What’s Coming Next

Antibiotic resistance is rising. Globally, 65% of Staph strains are resistant to erythromycin. In some areas, over 45% of staph infections are MRSA. That’s why new options are emerging.

Retapamulin (Altabax), a topical antibiotic approved for impetigo, showed 94% effectiveness in a 2024 trial with over 1,200 children. It’s a promising alternative for parents who want to avoid oral meds.

But the real game-changer might be faster diagnostics. The NIH is funding research into point-of-care tests that can identify the exact bacteria and its resistance profile in under 30 minutes. Right now, doctors guess based on symptoms. In the future, they’ll know - before prescribing - whether to use cephalexin or doxycycline. That could cut unnecessary antibiotic use by 40%.

The American Academy of Dermatology is pushing hard for antimicrobial stewardship - meaning no antibiotics unless absolutely needed. For mild rashes that look like impetigo but aren’t, watchful waiting or antiseptic washes might be enough.

When to Worry - Red Flags for Emergency Care

Not every red patch needs an ER visit. But some signs mean you need help immediately:

• High fever (over 101°F) with skin that looks burned or peeling - could be Staphylococcal Scalded Skin Syndrome (SSSS), which kills 2-5% of affected children.
• Redness spreading faster than 2 cm per day.
• Pain that gets worse instead of better after starting antibiotics.
• Swelling in the face, neck, or around the eyes.
• Confusion, rapid heartbeat, or trouble breathing.

If your child has these symptoms, call emergency services. SSSS can look like a sunburn but is a medical emergency. Cellulitis that spreads to the face or eyes can threaten vision or brain function.

Prevention: Simple Steps That Make a Big Difference

You can’t always stop infection, but you can cut your risk:

• Wash cuts and scrapes right away with soap and water. Apply an antiseptic like chlorhexidine.
• Don’t share towels, clothing, or razors - especially in households with kids or athletes.
• Treat athlete’s foot early. Those tiny cracks between toes are prime entry points for cellulitis.
• Keep fingernails short to prevent scratching open sores.
• If someone in the house has impetigo, wash bedding and towels daily in hot water.
• Children with impetigo should stay home from school or daycare until 24 hours after starting antibiotics - or until sores are dry and crusted.

During summer months, impetigo cases spike by 45%. That’s when kids are barefoot, playing in dirt, and sharing pool toys. Be extra vigilant.

Long-Term Risks and What Happens After

Impetigo usually clears without scars - but not always. About 5% of cases turn into ecthyma, a deeper infection that forms painful ulcers and leaves permanent scars. And if the infection was caused by Streptococcus, there’s a 1-5% risk of developing post-streptococcal glomerulonephritis, a kidney condition that can appear weeks later.

Cellulitis can recur. If you’ve had it once, your risk doubles. People with diabetes or chronic swelling in their legs (lymphedema or venous insufficiency) are especially prone. One study found those with venous insufficiency are 4.5 times more likely to get cellulitis again.

That’s why follow-up matters. Even if the redness fades, check in with your doctor if swelling returns, or if you notice new sores. Preventing recurrence means managing underlying conditions - controlling blood sugar, wearing compression socks, or treating fungal infections.

What You Should Know Before Your Next Doctor Visit

Don’t assume your doctor knows everything about your skin infection. Bring this info:

• When did it start? How fast did it spread?
• Have you had similar infections before?
• Are you diabetic, obese, or have poor circulation?
• Did you have a cut, bite, or foot fungus before this?
• Have you taken antibiotics recently? Which ones?

Ask: "Could this be MRSA?" If the infection doesn’t improve in 48 hours, insist on a culture or a change in treatment. Don’t accept "just keep taking the pill" if things are getting worse.

What Comes Next?

If you’ve had one bacterial skin infection, you’re at higher risk for another. Stay alert. Keep skin clean and moisturized. Treat minor wounds fast. Watch for signs of recurrence. And if you’re ever in doubt - don’t wait. A few hours can make the difference between a simple treatment and a hospital stay.