Cellulitis
A common bacterial infection of the skin and the soft tissue just beneath it, causing an area of skin that is red, warm, swollen and tender — usually on a leg. It spreads if untreated, so it needs antibiotics; a rapidly spreading or severely painful case needs urgent care.
What it is
Cellulitis is a bacterial infection of the deeper layers of the skin and the soft tissue below it. Bacteria — commonly streptococci or staphylococci — enter through a break in the skin, which may be as small as a crack between the toes, an insect bite, a cut, an ulcer or a patch of eczema. The infection then spreads through the tissue, producing a spreading area of skin that is red, warm, swollen and tender to touch, usually with a poorly defined edge. It most often affects a lower leg but can occur anywhere, including the face. There may also be fever and feeling generally unwell, and sometimes tender swollen glands nearby. It is diagnosed clinically from the appearance; blood tests can support it and gauge severity when the person is unwell. Most cases respond well to a course of antibiotics, with the redness settling over several days, though it can take a while for swelling to fully resolve. Left untreated it can spread and, uncommonly, lead to a serious deep infection or blood infection (sepsis). A small number of rapidly worsening, extremely painful infections signal a rare surgical emergency (necrotising fasciitis) that must be recognised urgently.
Key lab markers
- Full blood count (WBC and neutrophils) — often raised, reflecting infection.
- CRP and ESR — inflammatory markers, typically elevated; help gauge severity.
- Blood cultures — if the person is febrile or systemically unwell.
- Blood glucose — diabetes raises the risk and affects healing.
- Diagnosis is mainly clinical from the appearance; tests support severity assessment rather than confirm the diagnosis.
Symptoms
- An area of skin that is red, warm, swollen and tender
- A spreading edge to the redness, often poorly defined
- Usually on a lower leg, but can be anywhere
- Skin that may look tight, shiny or dimpled
- Fever and feeling generally unwell
- Sometimes tender, swollen glands nearby
- Often a break in the skin nearby (cut, bite, crack between the toes, ulcer)
Related symptoms
Related lab panels
When to discuss with a doctor
See a doctor promptly if you have an expanding area of red, warm, swollen and tender skin, especially with fever — cellulitis needs antibiotics and tends to spread if left. It helps to mark the edge of the redness so its spread can be watched. Seek urgent care if the redness is spreading quickly, the pain seems out of proportion to how the skin looks, the skin blisters or turns dusky, you develop a high fever, confusion or feel very unwell, or if cellulitis affects the face or the area around an eye — these can signal a more serious infection needing immediate treatment. People with diabetes, poor circulation, leg swelling or a weakened immune system should be seen early. Mediora.AI can point you to this topic and show any inflammatory-marker pattern, but cellulitis is diagnosed and treated by a doctor from the skin itself — starting treatment promptly is what prevents it spreading.