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Cellulitis is a bacterial infection of the deeper layers of skin and subcutaneous tissue, typically caused by Streptococcus pyogenes or Staphylococcus aureus. Skin abscesses are localized collections of pus within tissue spaces, often developing as complications of cellulitis or from direct bacterial inoculation through breaks in the skin.
Cellulitis occurs when bacteria penetrate compromised skin barriers through wounds, cracks, or medical devices, leading to spreading inflammation of dermis and subcutaneous fat. Abscesses form when the immune system walls off bacterial infections, creating a cavity filled with neutrophils, cellular debris, and bacteria that cannot be cleared by systemic antibiotics alone.
Diagnosis relies on clinical presentation of erythema, warmth, swelling, and tenderness, with cellulitis showing spreading borders and abscesses presenting as fluctuant masses. Treatment differs significantly: cellulitis responds to systemic antibiotics targeting gram-positive organisms, while abscesses require drainage plus antibiotic therapy, particularly covering MRSA in areas of high prevalence.