Synopsis
Recognise acute bacterial skin and soft-tissue infection, exclude common mimics and limb-threatening disease, choose oral or intravenous antibiotics by severity and review response within the expected trajectory.
- Cellulitis is an acute, usually unilateral, tender warm expanding infection of dermis and subcutis; erysipelas is more superficial, raised and sharply demarcated.
- Mark the edge with date and time when appropriate, but judge deterioration by physiology, pain, function and new features as well as millimetres of redness.
- Exclude an abscess, necrotising infection, septic joint, orbital disease and common non-infective mimics before issuing routine oral antibiotics.
- NICE first-choice adult oral treatment is flucloxacillin 500 mg to 1 g four times daily for five to seven days.
- Symptoms can worsen during the first 48 hours and skin may take time to normalise; improvement should begin within two to three days.
- Elevation, analgesia, hydration and treatment of tinea pedis, eczema, wounds and oedema support recovery and recurrence prevention.
- Do not routinely swab intact skin; culture pus, an open wound or a portal when unusual exposure, non-response or MRSA risk makes the result actionable.
- Refer to hospital for severe illness, rapid spread, oral-treatment failure with danger features, significant immune compromise or infection near the eye or nose.
Key red flags
Sepsis physiology, necrotising features, orbital or facial danger-site infection, compartment syndrome, septic joint, osteomyelitis, severe immunocompromise, rapidly spreading disease or inability to take oral treatment requires hospital assessment.
Pain out of proportion, rapid spread, skin anaesthesia, crepitus, haemorrhagic bullae, necrosis or shock demands immediate surgery.
Painful eye movements, reduced vision, proptosis, diplopia or ophthalmoplegia with periocular swelling indicates possible orbital cellulitis.
Investigation priorities
Identify systemic severity and determine hospital or intravenous-treatment need.
Management branches
Cellulitis is localised, the patient is stable, oral treatment is feasible and no danger-site or unusual exposure applies.
- Mark and document extent, portal, pain and observations, then start oral flucloxacillin for five to seven days after allergy assessment.
- Advise elevation, fluids, analgesia and treatment of toe-web fungal disease, eczema or wounds while avoiding compression during intolerable acute pain.
- Arrange review if not improving within two to three days and immediate help for systemic decline, rapid spread, blistering or severe pain.