An abscess is a confined pocket of pus that develops in tissue as the immune system attempts to isolate an infection. The English word comes from the Latin abscessus. Abscesses may form in the skin and soft tissues or within organs such as the liver, brain or teeth. They vary in size from small boil-like lesions to large collections that distort normal anatomy and can impair organ function.

Signs and characteristics

The typical local features are pain, heat, redness and swelling, and the area often feels fluctuant — that is, compressible and like it contains fluid. The surrounding area of erythema frequently extends beyond the central raised collection. Skin abscesses that arise in hair-bearing areas may begin as a follicle infection (a furuncle or "boil") and multiple adjacent infected follicles can coalesce into a carbuncle. Deep abscesses produce more subtle signs related to the affected organ and may present with fever, malaise or localized dysfunction.

Causes and microbiology

Most abscesses are caused by a bacterial infection, commonly involving more than one species; a variety of bacteria can participate in a single lesion. In many regions methicillin-resistant Staphylococcus aureus (MRSA) is a frequent pathogen for skin and soft tissue abscesses. Less commonly, microorganisms such as parasites or fungi produce abscesses — parasitic causes are seen more often in parts of the world with different epidemiology or sanitation patterns and may produce organ-specific abscesses related to travel or exposure risk (parasites).

Diagnosis and imaging

Superficial abscesses are usually diagnosed on clinical examination, but confirmation and assessment of extent can require imaging. Point-of-care ultrasound is useful to distinguish a fluid-filled collection from cellulitis and to guide aspiration. For perianal or deep pelvic collections (for example those around the anus) and for intra-abdominal or retroperitoneal collections, cross-sectional imaging such as computed tomography (CT) or magnetic resonance imaging helps define depth and connections and guides intervention.

Treatment and management

  • Incision and drainage: definitive treatment for most skin and soft-tissue abscesses is evacuation of the pus and debridement of necrotic tissue when present. Adequate drainage relieves pressure and removes the bulk of bacteria and inflammatory material.
  • Antibiotics: not always required for healthy people when drainage is complete, but indicated for systemic signs, spreading cellulitis, immunosuppression, certain locations (face, hand, perineum), or when high-risk organisms such as MRSA are suspected.
  • Wound care: recent evidence supports primary closure after adequate drainage for selected patients rather than traditional long-term packing; decisions are individualized by clinician and wound characteristics.
  • Needle aspiration alone may be insufficient for many abscesses and surgical opening is often necessary; image-guided percutaneous drainage is used for deep or organ-based collections.

Risks, prevention and notable facts

Complications include spread of infection, formation of fistulas, scarring and, in severe cases, bloodstream infection (sepsis). Risk factors for recurrent or extensive abscesses include diabetes, intravenous drug use, foreign bodies, poor hygiene and immunosuppression. Preventive measures emphasize wound hygiene, prompt treatment of superficial skin infections, harm-reduction practices for people who inject drugs, and control of underlying chronic conditions. Understanding when to seek care is important: worsening pain, fever, rapidly expanding redness, or signs of systemic illness all warrant medical evaluation.

Clinicians use the history, physical examination and selective imaging to decide between outpatient incision and drainage, antibiotic therapy or more invasive interventions. Public health attention to resistant organisms, sterile technique in healthcare settings and patient education all help reduce the burden of abscess disease.