Skip to main content

Health condition · Clinically reviewed

Cellulitis, antibiotics, red flags and stopping it coming back.

A spreading skin infection that responds well to prompt antibiotics - and needs urgent care when it doesn't. Here is how UK clinicians approach it.

Jump to treatment
A radiographer guides a patient onto the bed of an advanced 3 Tesla MRI scanner in a London imaging suite

Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against NICE NG141, CREST and BAD sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK antibiotic stewardship, ERON classification and recurrence prevention.

Key facts

Cellulitis at a glance.

The essentials, in plain English - what it is, which bugs cause it, and how UK antibiotics are chosen today.

  • What it is

    Acute bacterial infection of the skin and subcutaneous tissue, most often on the lower leg, causing spreading redness, warmth and swelling.

  • Main pathogens

    Beta-haemolytic streptococci (Groups A, C and G) most commonly, plus Staphylococcus aureus including MRSA and PVL-producing strains.

  • Special exposures

    Pasteurella after cat or dog bites, Vibrio from seawater, Aeromonas from freshwater and Erysipelothrix in butchers and fishermen.

  • Erysipelas

    A superficial variant with well-demarcated raised borders, classically on the face or leg.

  • First-line therapy

    Oral flucloxacillin 500 mg four times daily for 5 to 7 days in mild cellulitis, adjusted for allergy or severity.

  • Red flag

    Severe pain out of proportion, rapid progression, systemic toxicity or crepitus points to necrotising fasciitis - a surgical emergency.

Why this guide matters

Prompt antibiotics, careful review, prevention that lasts.

Cellulitis is common and usually straightforward, but a few situations turn it serious quickly. Three points shape the rest of this page.

  • Severity decides the setting

    ERON I is treated at home with oral flucloxacillin; ERON II to IV usually needs hospital admission for IV antibiotics.

  • Red flags cannot wait

    Severe pain out of proportion, orbital signs and rapid spread are not for a GP appointment next week - they are for A&E now.

  • Prevention beats recurrence

    Treat tinea pedis, venous eczema and lymphoedema, and consider prophylactic penicillin for recurrent episodes in the same site.

How the diagnosis is made

From a hot, red patch to a clear plan.

The steps a UK GP, out-of-hours doctor or acute team will normally follow - and why each one matters.

  1. 01

    Assessing

    Clinical assessment and border marking

    The border of the erythema is marked with a skin marker and dated so progression can be tracked hour by hour.

  2. 02

    Assessing

    ERON severity classification

    Grade I to IV guides whether care can be at home or needs hospital admission for intravenous antibiotics.

  3. 03

    Assessing

    Search for a portal of entry

    Interdigital tinea pedis, wounds, ulcers, insect bites, eczema and IV drug use sites are examined carefully.

  4. 04

    Confirming

    Bloods and cultures

    FBC, CRP and U&Es guide severity. Blood cultures are taken if febrile or systemically unwell, and a wound swab if the skin is broken.

  5. 05

    Confirming

    Imaging when needed

    Ultrasound for abscess, Doppler for suspected DVT and CT for orbital, deep or necrotising infection or suspected osteomyelitis.

  6. 06

    Confirming

    Exclude the mimics

    DVT, stasis dermatitis, lipodermatosclerosis, contact dermatitis, erythema migrans, septic arthritis, gout and Charcot arthropathy all need ruling out.

  7. 07

    Reviewing

    Plan review and safety-net

    Clear review points at 24 to 48 hours with instructions on when to return, escalate or attend A&E.

Typical timeline: first review to settling infection in days, not weeks.

Symptoms

What cellulitis actually looks like.

A hot, spreading, tender patch of skin plus systemic upset - with a few patterns that mean it's time to escalate straight away.

  • Well-demarcated erythema

    A hot, red, tender area with a spreading margin, usually unilateral - bilateral changes more often mean stasis dermatitis.

  • Warmth, swelling and tenderness

    The affected skin feels hot and taut, with pitting oedema and tenderness on light pressure.

  • Fever, rigors and malaise

    Systemic features suggest at least ERON II disease and warrant closer review, bloods and often admission.

  • Regional lymphadenopathy

    Tender lymph nodes upstream of the infection, sometimes with lymphangitic streaks tracking towards the groin or axilla.

  • Blisters, bullae, purpura or necrosis

    Signs of more severe disease - a trigger for admission, imaging and specialist input.

  • Erysipelas pattern

    A superficial, raised, sharply demarcated plaque - classically on the cheek or shin, often with fever at onset.

  • Periorbital and orbital signs

    Eyelid swelling and redness need same-day review. Proptosis, painful eye movement or reduced vision is a surgical emergency.

  • Red flag - necrotising fasciitis

    Severe pain out of proportion, dusky or purple skin, crepitus and rapid systemic decline. Urgent surgery and broad-spectrum antibiotics.

Treatment

How cellulitis is treated in the UK.

Flucloxacillin first for most, IV regimens for moderate to severe disease, and specific cover for bites, seawater exposure and MRSA.

  • Oral flucloxacillin

    First-line for mild cellulitis (ERON I) - 500 mg four times daily for 5 to 7 days, extended if slow to settle.

  • Clarithromycin or doxycycline

    Alternatives if there is true penicillin allergy, chosen for local sensitivities and patient factors.

  • IV benzylpenicillin + flucloxacillin

    Hospital regimen for moderate to severe cellulitis (ERON II to IV), switched to oral once clearly improving.

  • IV co-amoxiclav

    Used for facial cellulitis, animal bites and mixed infections to cover Pasteurella and oral anaerobes.

  • IV teicoplanin or vancomycin

    Reserved for MRSA cover, severe sepsis or where local resistance patterns require it.

  • Doxycycline with ceftriaxone

    For seawater-associated cellulitis with suspected Vibrio, especially in immunocompromised patients.

  • Prophylactic penicillin V

    250 to 500 mg twice daily for recurrent cellulitis (two or more episodes a year in the same site), alongside treating underlying causes.

  • Surgical debridement

    Urgent operative care for necrotising fasciitis, drainage of abscesses and management of deep or complicated infections.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and specialist society standards, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your GP, out-of-hours service or emergency department knows your skin and history and can tell you which parts apply to you. If in doubt, get seen.

  • NICE. Cellulitis and erysipelas: antimicrobial prescribing (NG141).

  • CREST. Guidelines on the management of cellulitis in adults.

  • British Association of Dermatologists (BAD). Cellulitis and erysipelas patient information.

  • NICE CKS. Cellulitis - acute.

  • UK Health Security Agency. Managing common infections guidance.

Red flags

When cellulitis needs urgent attention.

Most cellulitis settles with oral antibiotics. These are the situations where waiting is the wrong call.

  • Necrotising fasciitis

    Severe pain out of proportion to the visible signs, rapid progression, dusky skin, crepitus or systemic toxicity. This is a surgical emergency needing broad-spectrum antibiotics and theatre.

  • Orbital cellulitis

    Painful eye movement, proptosis or reduced vision alongside eyelid swelling. Needs urgent CT and specialist ophthalmology and ENT input.

  • Sepsis and systemic decline

    High fever, rigors, confusion, low blood pressure or rapid heart rate need urgent hospital care rather than oral antibiotics at home.

  • Failure to improve at 48 hours

    No settling of pain, spread or systemic signs within 48 hours of oral antibiotics warrants review, cultures and often admission for IV therapy.

  • Rapidly spreading erythema

    Advancing borders on the marked skin over hours rather than days - reassess for deeper infection and step up care.

  • Animal or human bite wounds

    Bites need co-amoxiclav cover, tetanus review and, for animal bites, rabies risk assessment based on species and location.

  • Immunocompromise or diabetes

    Lower threshold for admission, IV antibiotics and imaging - infection can progress quickly and mask usual signs.

  • Suspected DVT

    Unilateral calf swelling, tenderness and warmth can overlap with cellulitis. Doppler ultrasound helps separate the two.

  • IV drug use

    Cover Staph aureus, MRSA and mixed flora, consider PVL toxin and screen for endocarditis when systemically unwell.

Living with it

Treatable now, preventable next time.

Four things that make the biggest difference - treating the doorway on the skin, simple supportive care, thinking about prophylaxis, and knowing your red flags.

A quiet reminder

The best treatment for the next episode is preventing it.

Once you have had cellulitis, small habits - daily skin care, treating athletes foot, using compression when advised - stack up over months.

  1. 01 Skin care

    Treat the portal of entry

    Athletes foot, cracked heels, eczema and leg ulcers are the usual doorways. Fix them and recurrence drops sharply.

  2. 02 Support

    Elevate, hydrate, analgesia

    Elevate the affected limb above heart level when resting, keep well hydrated and use simple pain relief while antibiotics take effect.

  3. 03 Recurrence

    Ask about prophylaxis

    Two or more episodes a year in the same site is a trigger for long-term low-dose penicillin V and specialist follow-up.

  4. 04 Escalate

    Know your red-flag signs

    Rapid spread, severe pain, fever, confusion or eye symptoms - go straight to A&E rather than waiting for a GP slot.

Frequently asked

Everything we get asked about cellulitis.

Quick answers on antibiotics, admission thresholds, necrotising fasciitis and recurrence.

  • What is cellulitis?

    Cellulitis is an acute bacterial infection of the skin and the fatty layer underneath. It causes a hot, red, tender, spreading patch, usually on the lower leg, and often comes with fever and feeling generally unwell. Most cases are caused by beta-haemolytic streptococci or Staphylococcus aureus.

  • How is cellulitis different from erysipelas?

    Erysipelas is a more superficial form of the same family of infections. It has a raised, sharply demarcated border and often appears on the face or shin. The bacteria involved and the treatment approach overlap, but erysipelas tends to be more clearly outlined on the skin.

  • How is cellulitis treated in the UK?

    Mild cellulitis is treated with oral flucloxacillin 500 mg four times daily for 5 to 7 days, following NICE NG141. Clarithromycin or doxycycline are used for penicillin allergy. Moderate and severe disease needs hospital admission for intravenous antibiotics, sometimes including MRSA cover.

  • When does cellulitis need hospital admission?

    Admission is considered for ERON class II to IV disease - features include systemic toxicity, comorbidities such as diabetes or immunocompromise, rapid spread, facial or orbital involvement, failure of oral antibiotics, or an unstable social situation that prevents safe home care.

  • What warns of necrotising fasciitis?

    Severe pain that seems out of proportion to the visible skin changes, rapid progression, dusky or purple skin, blisters, crepitus under the skin and systemic collapse. It is a surgical emergency and needs immediate hospital care, broad-spectrum antibiotics and urgent operative debridement.

  • Can cellulitis come back, and how is that prevented?

    Yes - once you have had cellulitis in a limb the risk of recurrence is higher, especially with lymphoedema, venous disease or ongoing tinea pedis. For two or more episodes a year in the same site, NICE and CREST support long-term low-dose penicillin V alongside treating the underlying skin problem, weight management and compression where indicated.

Related content

Keep reading.

Pulse Healthcare concierge

Send us your enquiry

A concierge service for UK private healthcare. We match you with the best vetted clinics and consultants in our network - they then contact you directly.

So we can match you to the right clinician close to you.

We reply to every enquiry within 24 hours (Mon–Fri). Confidential - your details are never shared outside our vetted consultant network.