Abscess, furuncle and carbuncle !

Painful, pus-filled lumps in the skin, usually from staph bacteria. Large ones need draining; a cluster of linked boils is called a carbuncle.

Updated 2026-11-01

Structures involved

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Why it happens

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Hair follicles, sebaceous and sweat glands, nails

What it is

Purulent skin and soft-tissue infections. A skin abscess is a collection of pus in the dermis and subcutaneous tissue. A furuncle (boil) is a deep infection of a single hair follicle; a carbuncle is a group of furuncles joined under the skin with several draining points.

Who gets it

Very common in all ages and a frequent reason for emergency and primary-care visits. Community-acquired methicillin-resistant Staphylococcus aureus (MRSA) has become a leading cause in the Americas, including Colombia and other Latin American countries. Outbreaks occur in prisons, military units, contact sports teams and households.

Causes

Staphylococcus aureus in most cases, including MRSA
Streptococci and mixed flora, especially in perineal or perianal sites and in people who inject drugs
Entry through hair follicles, small cuts, insect bites or injection sites

Risk factors

Nasal or skin carriage of S. aureus
Diabetes mellitus, obesity and immunosuppression
Close contact, crowding, shared towels, razors or sports equipment
Injection drug use
Poor hygiene, friction and sweating (armpits, buttocks, neck)
Previous MRSA infection or recent hospitalisation

Pathophysiology

Bacteria invade a follicle or a break in the skin and attract neutrophils. Bacterial toxins (for example the Panton-Valentine leukocidin of many community MRSA strains) kill tissue and white cells, and the resulting pus is walled off by a fibrin capsule. The capsule limits spread but also keeps antibiotics from penetrating well, which is why drainage, not antibiotics, is the key treatment.

Classification

Furuncle: single follicle, often on the neck, face, armpit or buttocks
Carbuncle: several connected furuncles, typically on the nape of the neck or back
Simple skin abscess
Recurrent furunculosis
Severity: mild (no systemic signs), moderate, severe (systemic toxicity or immunosuppression)

Symptoms and signs

Red, warm, painful nodule that becomes soft and fluctuant
A yellow or white point (pustule) on top that may drain pus
Surrounding redness and swelling
Several draining openings in a carbuncle
Fever and malaise, more common with carbuncles or large abscesses

Diagnosis

Clinical: Clinical: a tender, fluctuant nodule, sometimes with a central pustule; look for spreading cellulitis and systemic signs.
Tests: Gram stain and culture of pus after drainage, especially for recurrent, severe or treatment-failing infections, to identify MRSA and guide antibiotics. Blood cultures and laboratory tests if systemic signs. Check glucose in recurrent cases.
Imaging: Bedside ultrasound confirms a fluid collection when it is unclear whether pus is present and guides drainage.

Differential diagnosis

Cellulitis without abscess
Inflamed epidermoid cyst
Hidradenitis suppurativa (recurrent nodules in armpits and groin)
Septic bursitis or septic arthritis
Myiasis (furuncular) in travellers or rural areas

Goal of treatment

Drain the pus, control infection and its spread, prevent recurrence and transmission, and recognise severe infection early.

Treatment

Conservative: Small furuncles: warm, moist compresses to promote spontaneous drainage; do not squeeze.
Procedure: Incision and drainage is the main treatment for fluctuant abscesses and carbuncles, with breaking of loculations and wound care.
Medical: Antibiotics are added for systemic signs, surrounding cellulitis, large or multiple abscesses, difficult sites, extremes of age or immunosuppression; empirical choices cover MRSA (e.g. trimethoprim-sulfamethoxazole, doxycycline or clindamycin; vancomycin intravenously for severe infection), adjusted to culture.
Follow-up: Wound checks, hand hygiene and contact precautions for draining wounds; decolonisation (nasal mupirocin, antiseptic washes) for recurrent infection.

Drugs for this condition

Dalbavancin

Complications

Cellulitis and lymphangitis
Bacteraemia, sepsis and seeding to bones, joints or heart valves
Cavernous sinus thrombosis from facial furuncles
Recurrence and spread to household contacts
Scarring

Prognosis

Most abscesses heal well after drainage, usually within one to two weeks. Recurrence is common with MRSA colonisation, diabetes or ongoing exposure.

Prevention

Hand hygiene and not sharing towels, razors or sports gear
Covering draining wounds until healed
Glycaemic control in diabetes
Decolonisation for patients with recurrent infection

Test yourself

Think of the answer, then tap the question to see it.

What is the most common cause of skin abscesses and furuncles?

Staphylococcus aureus, increasingly community-acquired MRSA.

What is the key treatment of a fluctuant skin abscess?

Incision and drainage; antibiotics are added only in selected cases.

How does a carbuncle differ from a furuncle?

A carbuncle is several interconnected infected follicles with multiple draining points, usually on the nape or back.

Why is a furuncle on the central face of concern?

Infection can spread through valveless facial veins to the cavernous sinus.

Which test helps when it is unclear whether a red swelling contains pus?

Bedside ultrasound.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Boils (MedlinePlus, US National Library of Medicine, 2026); Carbuncle (MedlinePlus, US National Library of Medicine, 2026); Methicillin-resistant Staphylococcus aureus (MRSA) Basics (Centers for Disease Control and Prevention (CDC), 2026).

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Skin highlighted on the Durgical 3D model