Cellulitis

Cellulitis is a common acute bacterial infection of the dermis and subcutaneous tissues. It typically presents with a localized area of redness, warmth, swelling, and tenderness, and may be accompanied by fever or malaise. While it most often affects the lower limbs, it can occur on any part of the body, including the face.

Causes and risk factors include disruption of the skin barrier from cuts, ulcers, insect bites, surgical wounds, dermatitis, or athlete’s foot. The most frequent pathogens are beta-hemolytic streptococci (such as Streptococcus pyogenes) and Staphylococcus aureus, including methicillin-resistant strains in some settings. Risk factors for more severe disease include diabetes, chronic edema, venous insufficiency, immune suppression, and skin conditions that promote moisture and bacterial growth.

Diagnosis is usually clinical. Key features are acute onset, localized infection, and signs of inflammation of the dermis and subcutaneous tissue. Blood tests and imaging are not routinely required but may be used when the presentation is atypical, if there is systemic illness, or to rule out abscess, deep infection, or involvement of adjacent structures. Cultures are often reserved for wounds, severe disease, or treatment failures.

Treatment depends on severity. Mild, non-purulent cellulitis can often be managed with oral antibiotics that cover streptococci and Staphylococcus aureus. Options include penicillin derivatives or cephalexin; if MRSA is a concern, alternatives such as doxycycline or trimethoprim-sulfamethoxazole may be used. More severe disease or systemic symptoms require intravenous antibiotics and hospital observation. Supportive care includes limb elevation and wound care; addressing precipitating factors like edema or dermatologic conditions is important.

Complications can include abscess formation, lymphangitis, bacteremia, osteomyelitis, septic arthritis, or, rarely, necrotizing fasciitis. Recurrence is common, particularly with ongoing edema or venous insufficiency. Prevention focuses on skin care, prompt treatment of breaks in the skin, and management of chronic risk factors.