Cellulitis

What it is

Cellulitis is a skin and soft tissue infection. Those infections split into the non-purulent, which are cellulitis, necrotizing fasciitis and erysipelas, and the purulent, which are impetigo and ecthyma, furuncle, carbuncle and abscess. Depth separates them further: erysipelas is superficial, cellulitis lies in the dermis and the subcutaneous tissue, and an abscess gives a localised fluctuation. Under the skin: epidermis, dermis, subcutaneous tissue and muscle. Cellulitis involves the deeper dermis and subcutaneous fat, while erysipelas involves the upper dermis and the superficial lymphatics, and there is clear demarcation between involved and uninvolved tissue. A skin abscess is a collection of pus within the dermis or subcutaneous space. Cellulitis and erysipelas both manifest as areas of skin erythema, edema and warmth.

The lexicon of the skin and soft tissue infections (SSTIs) is set out in two and it is worth reading as one list: the nonpurulent SSTIs are erysipelas, cellulitis and necrotizing infections, and the purulent SSTIs are impetigo or ecthyma, furuncle, carbuncle and abscess.