Cellulitis is a bacterial infection of the deeper skin, often starting where the skin barrier was broken by a cut, bite, ulcer or athlete's foot. It typically produces an area of skin that is red or discoloured, warm, swollen and tender, and that tends to spread outward over hours to days. It most commonly affects the lower legs but can occur anywhere.
Because cellulitis can worsen quickly and sometimes spread to the bloodstream, it usually needs prompt treatment with antibiotics from a doctor. Marking the edge of the redness with a pen can help you and a clinician judge whether it is spreading.
Seek same-day medical advice for suspected cellulitis, and urgent or emergency care if you develop fever, chills, rapidly spreading redness, severe pain out of proportion to the appearance, blistering, or you feel generally very unwell. Facial cellulitis and infections in people with diabetes or weak immunity need extra caution. This is general information only.