Cellulitis is frequently over-diagnosed.  Clinical signs need to include more than just redness  – other indications of inflammation are required for diagnosis – e.g. tenderness, pain, swelling, lymphangitis.  The onset and progression of the disorder is also a good pointer – streptococcal cellulitis has a rapid onset usually with rapid expansion of the erythematous zone.  New onset inflammation around a pre-existing leg ulcer that extends more than 1 cm from the edge may also indicate cellulitis (beware contact allergy from dressing materials however). 

Erysipelas, infection of the superficial dermis is associated with a sharply demarcated raised border and elevation of the involved skin. Cellulitis is a deeper process involving dermis and subcutaneous fat that causes brawny (less well-demarcated) oedema and a diffuse red border to the involved skin.

Conditions that may masquerade as cellulitis include: 

• Stasis dermatitis (also termed ‘venous eczema’) – brown skin pigmentation present from haemosiderin
• Altered vascular dynamics from disordered sympathetic control of vascular tone
• Contact allergy
• Resolved cellulitis – signs of resolution include cessation of the advance, fading redness, diminished oedema, skin peeling
• Other forms of dermatitis

Altered vascular tone

Lymphangitis

Resolving cellulitis in setting of severe chronic stasis dermatitis