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

What’s the Difference Between Impetigo and Cellulitis?

You wake up to find your child’s face covered in sticky, honey-colored crusts. Or maybe your leg suddenly swells, turns red, and feels hot to the touch. Both could be bacterial skin infections - but they’re not the same. Impetigo and cellulitis are among the most common skin infections you’ll see, especially in kids and older adults. One is mostly a surface problem. The other digs deep. Getting them mixed up can delay treatment and lead to serious complications.

Impetigo is a surface infection. It starts with tiny red sores, usually around the nose and mouth, that burst and leave behind a thick, golden crust. It’s contagious - think daycare centers, sports teams, or sharing towels. The main culprits are Staphylococcus aureus and sometimes Streptococcus pyogenes. These bacteria don’t always need a cut to get in; they can invade even healthy skin.

Cellulitis is deeper. It attacks the fat and tissue under the skin. You won’t see crusts. Instead, the area becomes swollen, warm, red, and tender - often with blurry edges. It can happen after a cut, insect bite, or even a crack in the skin from eczema. While Streptococcus is the usual cause, Staphylococcus can be involved too, especially if MRSA is around. Unlike impetigo, cellulitis doesn’t always look obvious at first. Many people mistake it for a bug bite or rash until it spreads.

Why Antibiotic Choice Matters - And Why It’s Not One-Size-Fits-All

Both infections are treated with antibiotics. But the right one depends on where you are, what bacteria are circulating, and whether the infection is mild or severe. A doctor in Wellington might prescribe something different than one in London or Paris - and that’s by design.

In the UK and Belgium, flucloxacillin is the go-to. It’s a penicillin-based antibiotic that works well against Staphylococcus aureus, the top cause of impetigo. For cellulitis, it’s also first-line unless there’s a known allergy. Over the past decade, its use for cellulitis has climbed from 41% to over 80% in some areas.

In France, doctors lean toward amoxicillin for cellulitis and pristinamycin for stubborn impetigo. Why? Because local resistance patterns show Streptococcus is more common in their cellulitis cases, and flucloxacillin doesn’t cover it as well. They’ve also seen rising MRSA rates, which means they’re avoiding broad-spectrum drugs unless necessary.

And then there’s MRSA - methicillin-resistant Staphylococcus aureus. This strain doesn’t respond to flucloxacillin, amoxicillin, or any penicillin-type drug. If you’ve had a skin infection that didn’t improve after a few days, or if you’ve been in a hospital or gym recently, MRSA is a real possibility. In those cases, doctors turn to clindamycin, doxycycline, or even vancomycin for severe cases.

Topical vs. Oral: When to Use Creams and When to Take Pills

Not every skin infection needs pills. For small, localized impetigo - say, one or two sores on the cheek - mupirocin ointment works brilliantly. Studies show it clears up 90% of cases within a week. You apply it three times a day for 5-10 days. No pills. No side effects. Just clean hands and a cotton swab.

But if the infection is spreading - more than five sores, or if it’s on the arms or legs - you need oral antibiotics. Same goes for cellulitis. Even if it looks small, it’s growing under the skin. Oral antibiotics like flucloxacillin or amoxicillin-clavulanate are needed for 7-10 days. If you’re allergic to penicillin, alternatives include clindamycin or doxycycline.

Here’s a quick rule: if you can cover the infected area with a postage stamp, try mupirocin. If it’s bigger, or if the skin feels hot and tight, you need oral meds. And if you have a fever, chills, or the redness is moving fast - go to the clinic. That’s not a wait-and-see situation.

Who’s at Risk - And Why Kids and Older Adults Are Most Vulnerable

Impetigo loves children, especially those between ages two and five. Why? They’re in close contact, they scratch, they don’t wash hands, and their skin is thinner. It spreads like wildfire in classrooms and playgroups. One kid with impetigo can infect half a class in a week.

Adults aren’t safe. Older adults, especially those with diabetes, poor circulation, or leg ulcers, are at high risk for cellulitis. A tiny scratch from a fall or a dry crack from winter skin can become an entry point. The infection can spread to the bloodstream - leading to sepsis - if not caught early.

People with eczema are double-risk. Their skin barrier is broken. Bacteria hang out in the cracks. That’s why many doctors recommend daily moisturizing and avoiding harsh soaps for eczema patients. It’s not just about comfort - it’s prevention.

Even healthy people can get infected if they share towels, razors, or sports equipment. Locker rooms, gyms, and swimming pools are hotspots. The CDC estimates over 14 million outpatient visits each year in the U.S. for skin infections like these. That’s a lot of missed work, school, and sleep.

What Happens If You Delay Treatment?

Impetigo might look harmless - just a few crusty spots. But if left untreated, it can lead to kidney problems (post-streptococcal glomerulonephritis) or spread to deeper tissues. Cellulitis? It’s a ticking clock.

After 48-72 hours without antibiotics, the infection can spread beyond the skin. It can reach the lymph nodes. It can enter the blood. It can cause abscesses, tissue death, or even toxic shock syndrome. In older adults or diabetics, cellulitis can lead to amputation if it reaches the foot.

One study found that patients who waited more than three days to start antibiotics had nearly double the risk of hospitalization. That’s not just inconvenient - it’s dangerous. If your skin is red, warm, and spreading - don’t wait until tomorrow. Go today.

Prevention: Simple Steps That Actually Work

You don’t need fancy products. Just basic hygiene.

• Wash cuts and scrapes immediately with soap and water. Cover them with a clean bandage.
• Don’t share towels, clothing, or razors - especially in households with kids or someone with eczema.
• Keep fingernails short. Scratching spreads bacteria.
• If someone in your home has impetigo, wash their bedding and clothes in hot water daily until they’re no longer contagious.
• For kids with impetigo, keep them home from school or daycare until they’ve been on antibiotics for at least 24 hours. Most schools require this.
• If you have diabetes or poor circulation, check your feet daily. Even a tiny blister can turn into cellulitis.

Antibiotic stewardship matters too. Don’t ask for antibiotics for a cold. Don’t use leftover pills. Misuse drives resistance. When your doctor prescribes flucloxacillin or mupirocin, take it exactly as directed - even if the redness fades after two days. Stopping early lets the toughest bacteria survive and multiply.

When to See a Doctor - And What to Expect

You don’t need to panic over every rash. But here’s when to act:

• Impetigo: Sores spreading, not improving after 3 days of mupirocin, or if you have a fever.
• Cellulitis: Redness spreading, swelling, pain, warmth, fever, chills, or if it’s near your eye or groin.

At the clinic, they’ll likely ask: How long has it been there? Did you have a cut or bug bite? Are you diabetic? Have you been in a hospital? They’ll check for swollen lymph nodes and may take a swab or blood test if it’s severe.

For mild impetigo, you’ll get mupirocin. For moderate to severe, you’ll get oral antibiotics. For cellulitis, you’ll almost always get oral meds - and if you’re very sick, you might need IV antibiotics in the hospital.

Most people feel better within 2-3 days. The redness fades. The swelling goes down. But the full course must be finished. That’s non-negotiable.

Final Thought: Don’t Guess - Get It Checked

Skin infections like impetigo and cellulitis are common, but they’re not harmless. What looks like a simple rash could be a fast-spreading infection. What seems like a minor crust could be a highly contagious condition that spreads through your whole family. The good news? Both respond well to the right antibiotics - if caught early.

Know the signs. Practice good hygiene. Don’t delay treatment. And if you’re unsure - see a doctor. It’s not overreacting. It’s protecting yourself, your kids, and your community.