History and exam

Key diagnostic factors

common

acute onset of red, painful, hot, swollen skin (cellulitis)

Spreads rapidly.[20][23] 

Most commonly occurs on the leg.[20][23][25] 

May have a well-demarcated or more diffuse border.[20][22][23] 

[Figure caption and citation for the preceding image starts]: Cellulitis of lower leg with open woundMartin Shields, Science Source, Science Photo Library [Citation ends].Cellulitis of lower leg with open wound

well-demarcated, bright-red raised skin (erysipelas)

Typically affects the face and lower limbs.[26]

The skin will often be fiery red with small vesicles on the surface.[20][34]

[Figure caption and citation for the preceding image starts]: Facial erysipelasCDC/Dr Thomas F. Sellers/Emory University [Citation ends].Facial erysipelas

Other diagnostic factors

common

orange-peel appearance

Also known as 'peau d’orange'.[20]

Caused by superficial oedema around hair follicles, which remain connected to the dermis.[20]

blistering

May occur within the area of cellulitis.[23]

bleeding

Superficial bleeding into blisters, or cutaneous haemorrhage, may present as petechiae or ecchymoses.[20][23][24]

lymphangitis

A red line that spreads proximally along lymphatics towards lymph nodes.[23] 

Seek advice from a senior decision-maker as this suggests that the infection is spreading to the lymphatic system.[21]

unilaterality

Bilateral leg cellulitis is rare.[23]

Practical tip

Unilaterality greatly increases the odds of cellulitis if diagnosis is uncertain in a patient with a red leg. Lack of warmth compared with the unaffected limb can help to exclude cellulitis.

Bear in mind that, although uncommon, bilateral cellulitis may complicate chronic dependent oedema or lymphoedema.[22]

fever

Temperature >38℃ (>100.4°F) indicates severe infection.[20]

malaise

May be associated with cellulitis and erysipelas.[23]

lymphadenopathy

May be associated with cellulitis and erysipelas.[23]

toe-web abnormalities

Evidence of fungal infection (tinea) may reveal the point of bacterial entry.[22] 

Fissures, scaling, and maceration may be a source of pathogen colonisation.[20]

risk factors

Infections can occur when bacteria breach the skin surface, particularly where there is fragile skin or decreased local host defences.[20] These situations may arise in association with:[21]

  • Diabetes[20][21]

    • For information about history and examination of diabetic foot, see our topic Diabetic foot infections 

  • Venous insufficiency[20][21]

  • Eczema[20][21]

  • Oedema and lymphoedema[20][21]

  • Obesity[20]

  • Toe-web abnormalities[20] 

    • Evidence of fungal infection (tinea) may reveal the point of bacterial entry[22] 

    • Fissures, scaling, and maceration may be a source of pathogen colonisation.[20]

uncommon

other constitutional symptoms

In practice, some patients report other constitutional symptoms such as rigors and nausea.

source of infection

Recent cutaneous trauma or surgery.[20] 

Toe-web abnormalities may indicate a common entry site for infection.[20]

immunocompromising factors

Risk for atypical organisms.

recent travel

May indicate the possibility of an unusual organism.

fluctuance deep to the cellulitis

In practice, this finding is rare. It indicates a possible abscess that may be associated with retained foreign material.

dermal necrosis

Occurs rarely in cellulitis.

  • May indicate necrotising fasciitis.[23]

signs of sepsis

The patient may present with non-specific or non-localised symptoms (e.g., acutely unwell with a normal temperature) or there may be severe signs with evidence of multi-organ dysfunction and shock.[27][28][29]

  • Remember that sepsis represents the severe, life-threatening end of infection.[35]

Ensure urgent review by a senior clinical decision-maker (e.g., ST4 level doctor in the UK).[28]

signs of necrotising fasciitis

Key signs include:

  • Rapid progression and pain out of proportion to clinical signs[31] 

  • Skin inflammation, swelling, and dusky discoloration[20] 

  • Numbness[20]

  • Subcutaneous tissue that feels wooden and hard, and that extends beyond the area of apparent skin involvement[20] 

  • High fever, disorientation, and lethargy[20]

  • Crepitus, which indicates gas in the tissues.[20]

See our topic Necrotising fasciitis. 

In practice, because this is life-threatening, refer the patient urgently (within 30 minutes of initial clinical assessment) for senior review, or to surgery or orthopaedics where patients with this condition are usually managed.

signs of orbital or peri-orbital cellulitis

In clinical practice, it may be difficult to differentiate between orbital and peri-orbital cellulitis. Key signs of orbital cellulitis include:

  • External eye muscle ophthalmoplegia and proptosis[39] 

  • Decreased visual acuity and chemosis[40] 

  • Blurred or double vision.[41] 

See our topic Peri-orbital and orbital cellulitis. 

Because this is a sight-threatening condition, refer the patient urgently to ophthalmology; in practice, refer within 30 minutes of initial clinical assessment.

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