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Cellulitis

Cellulitis is a bacterial infection of the deeper layers of the skin that causes an expanding area of redness, warmth, and swelling. It needs prompt antibiotic treatment.

Dermatologic
Cellulitis is a bacterial infection of the skin and the tissue just beneath it. It most often affects one lower leg, producing an expanding area of redness, warmth, swelling, and tenderness. Cellulitis is common and very treatable with antibiotics, but because the infection can spread quickly, it should be evaluated promptly rather than watched at home. Causes and Risk Factors: Cellulitis develops when bacteria — usually streptococci or Staphylococcus aureus — enter through a break in the skin. Common entry points and risk factors include:
  • Skin breaks: Cuts, scrapes, insect bites, puncture wounds, ulcers, and surgical incisions can all admit bacteria.
  • Athlete's foot: Cracked, macerated skin between the toes is one of the most common — and most overlooked — entry points for leg cellulitis.
  • Chronic leg swelling: Fluid buildup from vein problems or lymphedema stretches the skin and impairs local defenses; people with venous ulcer disease are at particular risk.
  • Diabetes: Diabetes slows healing and blunts the immune response, making infection easier to start and harder to stop.
  • Previous cellulitis: Having had cellulitis once makes a repeat episode in the same area more likely.
  • Bites and injection drug use: Animal and human bites and injections through unclean skin place bacteria directly into deeper tissue and often need broader antibiotic coverage.
Symptoms: Cellulitis usually develops over hours to a couple of days:
  • An expanding patch of red, warm, tender skin: The border often creeps outward; on darker skin the area may look purple, brown, or simply swollen and shiny.
  • Swelling and tightness: The affected limb can feel firm, heavy, and painful to touch.
  • Fever, chills, or feeling unwell: Signs that the infection is affecting the whole body.
  • One-sided involvement: True cellulitis rarely affects both legs at once; redness on both shins is more often an inflammatory skin condition than an infection.
  • Dimpling or blistering: The surface may take on a pitted, orange-peel texture, and small fluid-filled blisters can form over the most inflamed areas.
  • Tender lymph nodes: Glands in the groin or armpit on the affected side often swell and become sore as they filter the infection.
Diagnosis: There is no single blood test that confirms cellulitis; the diagnosis is made by examination, with blood counts or cultures checked when you are febrile or unwell. Because a blood clot in the leg can look similar — one warm, swollen, tender calf — your clinician may order an ultrasound to rule out deep vein thrombosis. Several other conditions mimic cellulitis, including chronic stasis skin changes from leg swelling, contact dermatitis, and an acute gout flare in a joint near the surface. Marking the edge of the redness with a pen and dating it helps show whether antibiotics are working. Treatment: Most cellulitis is treated at home, and improvement is usually visible within two to three days:
  • Oral antibiotics: Cephalexin covers the streptococci behind most cases; when MRSA (a resistant staph) is suspected — often when there is pus or an abscess — trimethoprim-sulfamethoxazole, doxycycline, or clindamycin is used instead.
  • Elevation and rest: Raising the affected leg above the level of the heart for much of the day reduces swelling and helps the redness recede.
  • Treating the entry point: Clearing athlete's foot, cleaning and dressing wounds, and moisturizing dry, cracked skin close the doorway the bacteria used.
  • Drainage when needed: A walled-off pocket of pus will not clear on antibiotics alone and has to be drained.
  • Intravenous antibiotics: Reserved for severe infection, high fever, rapid spread, or cellulitis that is not improving after a couple of days of oral therapy.
Complications: Untreated or under-treated cellulitis can form an abscess, spread into the bloodstream, or seed a nearby bone or joint. Repeated episodes also damage lymphatic drainage, leaving chronic swelling that makes the next infection more likely — which is why skin care and swelling control matter as much as the antibiotic course itself. When to Seek Immediate Care: Go to the emergency department for rapidly spreading redness, red streaks running toward the groin or armpit, high fever with shaking chills, confusion, blistering or blackening skin, or pain that feels far worse than the skin looks — these can signal a deeper, dangerous infection. After recovery, protecting the skin, moisturizing dry legs, and controlling swelling reduce the risk of another episode. The internal-medicine team at Zimmer Medical Group treats cellulitis and the conditions that invite it — schedule prompt care if a patch of skin is red, warm, and growing.

Related Medications

Commonly prescribed medications for this condition

CephalexinClindamycinDoxycyclineTrimethoprim-Sulfamethoxazole

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