Cephalexin (Keflex) is a first-generation cephalosporin antibiotic and a first-line treatment for uncomplicated skin infections like cellulitis, infected cuts, and impetigo. Typical adult dosing for skin infections is 500 mg every 6 to 12 hours for 5 to 10 days, with visible improvement usually within 48 to 72 hours. It covers the staph and strep species that cause most skin infections.
Skin and soft tissue infections drive over 14 million outpatient visits a year in the US, and cephalexin is one of the most prescribed answers. If a scrape has turned red and warm, or you keep a cephalexin course in an emergency kit, here’s what it does and how it’s used.
What counts as a skin infection cephalexin treats
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Cellulitis: spreading redness, warmth, swelling, and tenderness, usually on a leg. The classic cephalexin case
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Infected wounds: cuts, scrapes, and punctures that develop increasing redness, pus, or pain after a day or two
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Impetigo: the honey-crusted sores common in kids (topical mupirocin handles small patches; oral cephalexin handles widespread cases)
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Folliculitis and small abscesses: alongside drainage when needed, since antibiotics don’t replace draining a pocket of pus
What it doesn’t reliably cover: MRSA. If an infection features a painful boil or abscess, came from a gym, locker room, or healthcare setting, or worsens on cephalexin, MRSA is the suspect and different antibiotics (like TMP-SMX or doxycycline) come into play. This is exactly the judgment call a prescribing provider is making when they ask about your infection’s appearance and history.
Dosage and course
|
Detail |
Typical adult use for skin infections |
|---|---|
|
Dose |
500 mg capsule |
|
Frequency |
Every 6 to 12 hours depending on severity (often 4 times daily for cellulitis) |
|
Course |
5 to 10 days |
|
With food? |
Optional; food helps if it upsets your stomach |
Mark the improvement clock when you start: redness and pain should stop spreading within 24 to 48 hours and clearly recede by 72. A trick providers use that you can too: trace the redness border with a pen when you begin treatment. If redness crosses the line and keeps going, the antibiotic isn’t winning and you need reevaluation, urgently if there’s fever.
Side effects and the penicillin question
Cephalexin is one of the better-tolerated antibiotics. Most common: diarrhea, nausea, and stomach upset. Taking it with food and a probiotic-friendly diet helps. Severe watery diarrhea during or after a course needs medical attention (C. diff risk, as with any antibiotic).
The classic question: can you take cephalexin with a penicillin allergy? Old teaching said 10% cross-reactivity; modern data puts true cross-reactivity with cephalexin far lower, around 1% or less for most penicillin-allergic patients. But anyone with a history of anaphylaxis to penicillin should treat this as a provider conversation, not a calculated risk taken alone.
Why cephalexin belongs in an emergency kit
Skin infections are among the most common reasons people need antibiotics when access is cut off: post-hurricane cleanup is a cellulitis factory (debris cuts plus flood water), and backcountry trips turn small wounds into big problems. That’s why cephalexin appears in physician-designed preparedness kits. Through OZIO, a licensed physician reviews your health history online and, if appropriate, prescribes cephalexin 500 mg individually or as part of a broader emergency kit, shipped from a US pharmacy.
FAQ
How fast does cephalexin work on a skin infection?
Bacterial killing starts within hours; visible improvement typically shows at 48 to 72 hours. No improvement by 72 hours means reevaluation, not more waiting.
Is cephalexin stronger than amoxicillin for skin infections?
Not stronger, better aimed. Cephalexin’s staph coverage is more reliable than plain amoxicillin’s, which is why it’s preferred for skin. For dental or sinus infections the ranking flips.
Can cephalexin treat MRSA?
No. Suspected MRSA (abscesses, boils, infections that worsen on cephalexin) needs different antibiotics and often drainage.
Can I drink alcohol on cephalexin?
Moderate alcohol doesn’t interact with cephalexin the way it does with metronidazole. Hydration still helps you heal.
This article is for informational purposes only and is not medical advice. Antibiotics require an evaluation by a licensed healthcare provider. Seek immediate care for rapidly spreading redness, red streaks, fever, or infections on the face or hands.
