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

Two kids come home from school with red, crusty sores around their noses. A few days later, an adult wakes up with a swollen, hot patch on their leg that won’t go away. Both have bacterial skin infections-but they’re not the same. One is impetigo, the other is cellulitis. Mistake one for the other, and you could delay treatment, spread the infection, or even risk serious complications.

What Impetigo Looks Like-and How It Spreads

Impetigo is the most common bacterial skin infection in children, especially between ages 2 and 5. It’s contagious, fast-spreading, and often called "school sores" for a reason. You’ll see it in daycare centers, sports teams, and crowded households.

There are two types. The most common-about 70% of cases-is nonbullous impetigo. It starts as small red bumps or blisters, usually around the nose and mouth. Within hours, they burst, ooze, and form a thick, honey-colored crust. It doesn’t hurt much, but it itches. Kids scratch, then spread it to their hands, arms, or legs.

The other type, bullous impetigo, is less common. It shows up as larger, fluid-filled blisters (2-5 cm wide) that look like balloons. They’re fragile and pop easily, leaving behind a raw, red area with a ring-like border. These are more likely to appear on the trunk or diaper area.

What causes it? Mostly Staphylococcus aureus, sometimes Streptococcus pyogenes. These bacteria don’t always need broken skin to get in-they can invade healthy skin. But they love it when there’s a cut, scrape, insect bite, or eczema flare-up. That’s why kids with dry, itchy skin are more likely to get it.

It spreads fast. Touching the sores, sharing towels, or even just being in the same room can pass it along. The CDC says bacterial skin infections like this are among the top 30 reasons people visit doctors. In the U.S., over 14 million outpatient visits each year are for skin and soft tissue infections-and impetigo makes up a big chunk.

What Cellulitis Is-and Why It’s More Dangerous

Cellulitis is deeper. It doesn’t just sit on the surface. It burrows into the dermis and fat layer under the skin. That’s why it’s more serious.

You’ll notice a red, swollen, warm patch that feels tender to the touch. The edges are blurry, not sharp. It often shows up on the lower legs, but it can happen anywhere-arms, face, even around the eyes. Sometimes, fluid leaks out. In severe cases, you might get fever, chills, or feel generally sick.

Unlike impetigo, cellulitis rarely causes crusts or blisters. Instead, the skin looks like it’s been bruised or swollen from an injury-even if there wasn’t one. People often mistake it for a bug bite or a rash at first. That’s dangerous. Delayed treatment can lead to abscesses, sepsis, or even tissue death.

Most cases are caused by Streptococcus bacteria, though Staphylococcus aureus is also common. If the infection comes from a cut or wound, MRSA (methicillin-resistant Staphylococcus aureus) is a growing concern. MRSA doesn’t respond to common antibiotics like amoxicillin or cephalexin. It needs stronger drugs.

People with diabetes, poor circulation, or weakened immune systems are at higher risk. So are older adults and those with leg swelling from heart or vein problems. A 2022 study from Orem Dermatology Center found that the average cellulitis episode lasts 7-10 days with treatment. Without it? It can turn life-threatening in under 48 hours.

Antibiotic Choices: What Works and What Doesn’t

Both infections need antibiotics-but not the same ones. And where you live matters.

For impetigo, if it’s limited to a few spots, topical mupirocin (Bactroban) works well. Studies show it clears up 90% of cases in under a week. But if it’s spread out, or if the child has a fever or swollen lymph nodes, you need oral antibiotics. In the UK and Belgium, flucloxacillin is the go-to. In France, doctors often use amoxicillin-clavulanate or pristinamycin. Why the difference? Resistance patterns. In some areas, staph has grown resistant to flucloxacillin. In others, it still works fine.

For cellulitis, the first-line oral antibiotic is usually amoxicillin-clavulanate or cephalexin. But if MRSA is suspected-like if the person has had recent hospital stays, IV drug use, or lives in a community with high MRSA rates-doctors switch to clindamycin or doxycycline. In severe cases, hospitalization and IV antibiotics like vancomycin are needed.

Here’s a quick comparison:

First-Line Antibiotics for Impetigo and Cellulitis by Region

Condition	UK & Belgium	France	US Guidelines
Impetigo (mild)	Mupirocin cream	Mupirocin cream	Mupirocin cream
Impetigo (widespread)	Flucloxacillin	Amoxicillin-clavulanate or pristinamycin	Cephalexin or dicloxacillin
Cellulitis (no MRSA)	Flucloxacillin	Amoxicillin	Cephalexin or amoxicillin-clavulanate
Cellulitis (MRSA suspected)	Clindamycin or doxycycline	Clindamycin	Clindamycin or trimethoprim-sulfamethoxazole

Doctors now avoid using broad-spectrum antibiotics unless they have to. Overuse leads to resistance. That’s why culture and sensitivity tests are recommended for recurrent cases, treatment failures, or if MRSA is suspected. In 65% of those cases, labs now test for resistant strains before prescribing.

When to See a Doctor-And When to Worry

For impetigo: Call your doctor if the sores spread quickly, don’t improve after 3 days of treatment, or if your child has a fever. Don’t wait for it to get worse. It’s contagious. Keep kids home until they’ve been on antibiotics for at least 24 hours.

For cellulitis: Go to urgent care or the ER if you see any of these signs:

• Redness spreading rapidly (more than 1 inch per hour)
• Fever, chills, or nausea
• Severe pain or numbness in the area
• Red streaks leading away from the infection
• Swelling that makes it hard to move a limb

These could mean the infection is entering your bloodstream. That’s sepsis territory. Emergency treatment is needed.

Even if it doesn’t seem bad, don’t try to treat either infection with leftover antibiotics. A wrong drug can make things worse. And never squeeze or pop the sores. That spreads bacteria.

Prevention: Stop It Before It Starts

The best treatment is avoiding infection in the first place.

• Wash hands often-especially after touching sores or bandages.
• Clean and cover cuts, scrapes, or insect bites right away.
• Don’t share towels, clothing, or razors.
• Keep skin moisturized if you have eczema or dry skin.
• If someone in your home has impetigo, wash their bedding and clothes daily in hot water.
• For people with diabetes or poor circulation, check feet and legs daily for redness or breaks in the skin.

Doctors are starting to focus more on "antibiotic stewardship"-using the right drug, at the right dose, for the right time. A 2023 study predicted that within five years, doctors will cut unnecessary antibiotic use by 40% by using faster tests to identify the exact bacteria and its resistance profile.

That means less resistance. Fewer side effects. Better outcomes.

What Happens If You Don’t Treat It?

Impetigo usually clears up on its own-but not without risk. Untreated, it can lead to kidney inflammation (post-streptococcal glomerulonephritis), especially in children. It also spreads like wildfire. One child with impetigo can infect half a classroom in a week.

Cellulitis? It doesn’t wait. Left untreated, it can turn into:

• An abscess (a pocket of pus that needs draining)
• Necrotizing fasciitis (a rare but deadly "flesh-eating" infection)
• Sepsis (body-wide inflammation that can shut down organs)
• Recurrent infections (up to 20% of people get it again within a year)

That’s why early treatment is non-negotiable. Most people feel better within 2-3 days of starting antibiotics. But they must finish the full course-even if the redness is gone. Stopping early lets the toughest bacteria survive and come back stronger.

Final Thought: Don’t Guess. Get Tested.

These infections look similar at first glance. But the treatment? Totally different. A rash that seems harmless could be the start of something dangerous. A crusty sore might look like a minor annoyance-but it’s contagious and can spread fast.

The key is knowing when to act. If you’re unsure, see a doctor. Don’t wait. Don’t self-diagnose. And don’t share antibiotics. The right treatment starts with the right diagnosis-and that means letting a professional identify the bacteria behind the redness.