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, their mom wakes up with a swollen, hot patch on her leg that hurts to touch. Both have skin infections-but they’re not the same. One is impetigo, the other is cellulitis. They look similar at first glance, but they’re different in how they spread, how deep they go, and most importantly, how they’re treated.

What Impetigo Really Looks Like

Impetigo is the classic "school sores" infection. It’s everywhere in daycare centers and primary schools, especially in kids aged 2 to 5. You’ll see small red blisters or sores, usually around the nose, mouth, or hands. They don’t stay as blisters for long. Within hours, they burst and leave behind a sticky, honey-colored crust. That’s the hallmark. It’s not usually painful, but it’s incredibly itchy-and contagious.

There are two types: nonbullous (70% of cases) and bullous. Nonbullous is what most people think of-those crusty patches. Bullous impetigo is rarer. It shows up as larger, fluid-filled blisters, 2 to 5 cm across, that look like they’re about to pop. When they do, they leave a thin, ring-like edge. It’s more common in babies and younger children.

What causes it? Mostly Staphylococcus aureus, sometimes Streptococcus pyogenes. These bacteria don’t even need a cut to get in. They can invade healthy skin, especially if it’s dry, irritated from eczema, or already scratched from bug bites. Once one kid has it, it spreads fast-through towels, toys, shared clothing, or even just touching.

What Cellulitis Actually Is

Cellulitis is deeper. It’s not just on the surface. It’s an infection of the dermis and the fatty tissue underneath. You’ll notice a red, swollen, warm, and tender area on the skin-often on the lower legs, but it can happen anywhere. The edges are blurry, not sharp. It doesn’t crust over like impetigo. Instead, the skin might feel tight, look shiny, and sometimes leak clear or yellow fluid.

It’s not just a rash. It’s an infection that’s spreading under the skin. If left untreated, it can move toward the bloodstream, causing fever, chills, and even sepsis. That’s why it’s treated as seriously as it is. Unlike impetigo, cellulitis rarely spreads person-to-person. It usually starts from a break in the skin-a cut, a burn, a fungal infection between the toes, or even a bug bite.

Most cases are caused by Streptococcus bacteria, especially group A Streptococcus. But Staphylococcus aureus is also common. And here’s the twist: more than 30% of cases now involve MRSA-methicillin-resistant Staphylococcus aureus. That’s the strain that laughs at regular antibiotics like amoxicillin or flucloxacillin.

Why the Treatment Is Totally Different

You might think, "Both are bacterial skin infections-why not just give the same antibiotic?" But that’s where things go wrong.

For mild impetigo, you don’t even need pills. Topical mupirocin ointment applied three times a day for 7 to 10 days works in about 90% of cases. It’s cheap, targeted, and keeps the infection from spreading. If it’s widespread or not improving, then oral antibiotics like cephalexin or dicloxacillin are used.

Cellulitis? You can’t just rub something on it. It needs to go deep. Oral antibiotics like flucloxacillin, cephalexin, or amoxicillin-clavulanate are standard. But here’s the catch: if you’re in Australia, the UK, or Canada, flucloxacillin is the go-to. In France, doctors often start with amoxicillin. In Belgium, there’s no official guideline-so it’s up to the doctor’s experience.

And if it’s MRSA? Flucloxacillin won’t touch it. You need clindamycin, doxycycline, or trimethoprim-sulfamethoxazole. That’s why doctors are starting to test cultures more often-especially if the infection doesn’t improve after 48 hours, or if the patient has diabetes, a weak immune system, or has been in the hospital recently.

Regional Differences in Antibiotic Use

Antibiotic choices aren’t the same everywhere. In the UK, flucloxacillin prescriptions for cellulitis jumped from 41% to over 51% between 2018 and 2023. In France, amoxicillin use for cellulitis nearly doubled in the same period. For impetigo, the UK and Belgium rely heavily on flucloxacillin-prescriptions climbed to over 80%. But in France, they’re using pristinamycin and amoxicillin-clavulanate more, because resistance to older drugs is rising.

Why the difference? It’s all about local resistance patterns. In some areas, MRSA is rare. In others, it’s everywhere. Doctors in Adelaide, for example, are seeing more MRSA in community-acquired infections than they did five years ago. So they’re starting to think twice before prescribing flucloxacillin for someone who doesn’t improve quickly.

That’s why the best approach isn’t one-size-fits-all. It’s about knowing your community’s bugs. If you’re treating a child with impetigo in a school where 10 kids had it last month, you might skip the culture and just start mupirocin. But if you’re treating an older adult with diabetes and a leg infection that’s getting worse after two days of amoxicillin, you need a culture-and maybe a hospital admission.

When to Worry: Red Flags for Both Infections

Most cases are mild and clear up with treatment. But some turn dangerous fast.

For impetigo, worry if:

• The sores spread rapidly over large areas of the body
• The child develops a fever or seems unusually tired
• The skin around the sores becomes swollen, red, and hot (signs it’s turning into cellulitis)

For cellulitis, the red flags are clearer:

• Fever or chills
• The red area spreads quickly-like 1 cm per hour
• Red streaks running up the leg or arm
• Numbness, tingling, or blistering in the infected area
• Diabetes, poor circulation, or a weakened immune system

If you see any of these, don’t wait. Go to a clinic or ER. Cellulitis can turn into sepsis in under 24 hours if ignored.

Prevention Is Simpler Than You Think

You can’t always avoid these infections, but you can cut the risk big time.

For impetigo:

• Wash hands often-especially after touching sores
• Don’t share towels, bedding, or clothing
• Cover sores with a clean bandage
• Keep kids home for at least 24 hours after starting antibiotics
• Treat eczema well-dry, cracked skin is an open door for bacteria

For cellulitis:

• Clean every cut, scrape, or bite with soap and water
• Apply antibiotic ointment and cover it
• Watch for swelling or redness after injury-don’t ignore it
• If you have diabetes, check your feet daily
• Don’t delay treating athlete’s foot-it can lead to cracks that become infected

And if you’ve had cellulitis before? You’re at higher risk for it again. Doctors may prescribe a low-dose antibiotic long-term to prevent recurrence-especially if you have chronic swelling in your legs.

How Long Does It Take to Get Better?

With the right treatment:

• Impetigo: Crusts start to fade in 3 to 5 days. Sores heal completely in 7 to 10 days.
• Cellulitis: Redness and swelling should improve within 48 to 72 hours. Full recovery takes 5 to 14 days.

If you don’t see improvement in 2 days, call your doctor. That’s the golden window. Delayed treatment means the infection spreads deeper, and you might need IV antibiotics in the hospital.

And don’t stop antibiotics just because it looks better. Finish the full course. Stopping early is how MRSA becomes resistant in the first place.

What About Natural Remedies or Home Treatments?

Some people try tea tree oil, honey, or garlic pastes. There’s no strong evidence they work for impetigo or cellulitis. In fact, using them instead of antibiotics can be dangerous. These infections aren’t like a cold-they don’t get better on their own. Bacteria multiply fast under the skin. Waiting for "natural healing" can mean the difference between a quick fix and a hospital stay.

What does help? Keeping the area clean, dry, and covered. Warm compresses can ease pain from cellulitis. But they don’t kill the bacteria. Antibiotics do.