Cellulitis

Cellulitis is a common bacterial infection of the deeper layers of the skin and the tissue beneath. It usually appears as a red, swollen, warm, and painful area of skin, often on the lower legs, but it can occur anywhere. The most frequent causes are streptococci and Staphylococcus aureus, including MRSA in some communities.

Cellulitis can spread rapidly and, if untreated, may lead to serious complications such as bacteremia, abscess, or necrotizing infection. Most cases respond well to oral or intravenous antibiotics. People with recurrent cellulitis may need preventive strategies addressing underlying risk factors such as lymphedema, athlete’s foot, or chronic venous disease.

Signs and symptoms of cellulitis include:

• Redness and swelling that expands over hours to days
• Warmth and tenderness of the affected skin
• Pain
• Skin that appears tight or glossy
• Possible dimpling or “orange-peel” appearance
• Fever, chills, and feeling ill in more severe cases
• Red streaks extending from the area (lymphangitis)
• Swollen nearby lymph nodes

An abscess may form as a fluctuant, painful collection of pus. Severe pain out of proportion to skin findings, rapid progression, or systemic toxicity can signal deeper or necrotizing infection.

Cellulitis occurs when bacteria enter through a break in the skin — cuts, scrapes, surgical wounds, insect bites, ulcers, athlete’s foot, or dermatitis. The most common organisms are beta-hemolytic streptococci and Staphylococcus aureus. In specific settings, other organisms may be involved (Pasteurella after cat/dog bites, Aeromonas or Vibrio after water exposure, etc.). Infection of deeper structures or necrotizing fasciitis is a different, more severe process that requires urgent surgical evaluation.

Risk factors include:

• Cuts, insect bites, surgical incisions, or skin conditions that break the barrier (eczema, athlete’s foot, shingles)
• Chronic leg swelling (lymphedema, venous insufficiency)
• Obesity
• Diabetes and peripheral vascular disease
• Weakened immune system
• Previous cellulitis
• Intravenous drug use
• Tinea pedis (athlete’s foot) as a portal of entry for leg cellulitis

Possible complications include:

• Abscess formation
• Bacteremia and sepsis
• Lymphangitis and chronic lymphedema after repeated episodes
• Osteomyelitis or septic arthritis if infection spreads to bone or joint
• Necrotizing soft-tissue infection (rare but life-threatening)
• Recurrent cellulitis in the same area

To reduce risk:

• Clean and protect cuts and scrapes promptly
• Treat athlete’s foot, eczema, and other skin breaks
• Moisturize dry skin to avoid cracking
• Manage chronic leg swelling with elevation and compression when appropriate
• Maintain good foot care, especially with diabetes
• For recurrent cellulitis, discuss prophylactic antibiotics and management of predisposing conditions with a clinician

Diagnosis is primarily clinical. Blood cultures are considered in patients with fever, severe illness, or immunocompromise. Wound or abscess cultures guide therapy when drainage is present. Imaging (ultrasound, CT, MRI) may be used when abscess, deep infection, or alternative diagnoses (DVT, osteomyelitis) are suspected. Marking the border of redness helps monitor progression.

Seek medical care promptly for expanding redness, warmth, and pain in the skin, especially with fever. Go to the emergency department for rapidly spreading infection, severe pain, blistering, purple discoloration, confusion, rapid heartbeat, or if you have a compromised immune system or are very young or elderly.

Antibiotics are the mainstay of treatment:

• Oral antibiotics for mild, uncomplicated cellulitis (e.g., cephalexin, dicloxacillin, or agents covering MRSA when risk factors are present — such as trimethoprim-sulfamethoxazole, clindamycin, or doxycycline, according to local resistance patterns)
• Intravenous antibiotics for severe infection, systemic signs, rapid progression, or inability to take oral medicine
• Elevation of the affected limb and pain control
• Drainage of abscesses when present
• Hospitalization and surgical consultation if necrotizing infection is suspected
• Adjustment of therapy based on culture results and clinical response

Typical duration is 5–14 days depending on severity and response. Improvement is usually seen within 48–72 hours.

While treating cellulitis:

• Take the full antibiotic course
• Elevate the affected area above heart level when possible
• Rest the area and avoid straining the affected limb
• Keep the skin clean and follow wound-care advice
• Monitor the border of redness and systemic symptoms
• Return promptly if spreading continues, fever worsens, or new symptoms develop

Bring:

• When the redness started and how quickly it has spread
• History of skin breaks, athlete’s foot, swelling, or prior cellulitis
• List of medicines and allergies (especially antibiotic allergies)
• Medical conditions such as diabetes or lymphedema
• Questions about oral vs IV therapy and prevention of recurrence