cellulitis
Meaning of cellulitis: Redness appearing on both legs at once is rarely cellulitis, since the infection almost always settles on one side only.
Definition of cellulitis
Cellulitis is a bacterial infection of the deeper layer of skin and the fatty tissue beneath it. Bacteria usually enter through a break in the surface, such as a cut, a bite, a crack between the toes or a patch of eczema, though no entry point is found in many cases. The affected skin turns red, warm, swollen and tender.
Which bacteria cause it, and how does it spread?
Two groups account for most cases. Streptococci spread rapidly through tissue planes and produce a diffuse, fast-moving redness. Staphylococcus aureus is more often involved when there is a wound, an abscess or pus. Once past the surface, the bacteria multiply in the dermis and the soft tissue below, and the visible redness is largely the immune response rather than the organisms themselves. Spread follows the lymphatic channels, which is why tender lymph nodes may swell in the groin or armpit and why a red streak sometimes tracks up the limb. Fever, chills and a raised white cell count show the response has become systemic.
What is it confused with?
| Condition | How it differs |
|---|---|
| Erysipelas | More superficial; the border is raised and sharply defined rather than fading out |
| Stasis dermatitis | Both legs, chronic, itchy rather than tender, with skin staining from old blood |
| Deep vein thrombosis | Swelling and pain with less redness and no entry wound |
| Contact dermatitis | Itchy and sharply shaped to whatever touched the skin |
| Necrotizing fasciitis | Pain far out of proportion to appearance, rapid change, systemic collapse |
Misdiagnosis runs mainly in one direction. A large share of people admitted for lower-leg cellulitis turn out to have one of the mimics instead, and the bilateral pattern is the most useful warning that the label may be wrong.
What raises the risk of it recurring?
Anything that damages the skin barrier or the drainage beneath it. Athlete's foot cracks the skin between the toes and is a common silent doorway. Persistent leg swelling from lymphedema or venous disease impairs the clearance of organisms, and every episode of infection scars lymphatic channels a little further, so each attack makes the next one likelier. Obesity, diabetes, eczema and previous surgery to lymph nodes all contribute. Because the redness may keep spreading for a day or two after treatment begins, its border is sometimes marked so that later change can be judged against a fixed line rather than memory.
Used in a sentence
The area of spreading redness and warmth on the leg was diagnosed as cellulitis.
Good to know
The spreading, poorly defined redness of cellulitis is distinguished from the sharply demarcated rash of erysipelas, a related but more superficial skin infection, and redness affecting both legs symmetrically is more often a mimic than true cellulitis.
Word origin
Where “cellulitis” comes from
Formed from Latin cellula, meaning small cell or chamber, combined with -itis, from Greek, indicating inflammation.