Furuncles, carbuncles & cutaneous abscess
Also called boil, furunculosis, skin abscess
The follicular deep end of staphylococcal skin disease: boils, their multi-headed cousin the carbuncle, and the walled-off abscess. One management idea dominates: pus under pressure needs a way out.
How it looks
A tender, fluctuant erythematous nodule with a central pustular point, surrounded by firm induration, at a hair-bearing site.
Rose is the lesion, grey the pattern the lesions make, green where on the body it lives.
Across skin tones
Erythema around a deep abscess can be nearly invisible in deeply pigmented skin; rely on tenderness, warmth, induration, and fluctuance, and compare with the opposite side rather than hunting for redness.
Don't miss
A 'boil' in the central face triangle can propagate to the cavernous sinus; drain gently, treat systemically, and never squeeze.
Forms & variants
Furuncle (boil)
A deep staphylococcal infection of one follicle: a tender red nodule that points, fluctuates, and discharges.
Carbuncle
Several adjacent follicles infected in continuity, a boggy multi-headed plaque draining through multiple sinuses, classically the nape; more systemic upset, more scarring.
Cutaneous abscess
A walled-off pus collection not necessarily born of a follicle; fluctuance is the sign, and drainage, not antibiotics, is the cure.
Symptoms & course
- Localized throbbing pain and tenderness
- Fluctuance as pus organizes
- Fever mainly with carbuncles or spreading infection
Diagnostic approach
- Clinical; ultrasound when fluctuance is equivocal
- Swab the pus at drainage for culture
- Recurrent boils: swab carriage sites and think decolonization, diabetes, immunosuppression
Differential, and how to separate them
- Acne vulgaris
Favours it: Inflamed nodules in a young patient
Against it: Acne brings comedones and a polymorphic field; a solitary exquisitely tender fluctuant nodule is a boil
- Cellulitis
Favours it: A hot, red, tender area
Against it: Cellulitis is diffuse without a drainable point; an abscess is focal and fluctuant, and ultrasound settles it
Management principles
- Incision and drainage is definitive for fluctuant lesions
- Antibiotics only for surrounding cellulitis, systemic features, or high-risk sites
- Recurrent furunculosis: hygiene measures and staphylococcal decolonization
Clinical pearl: Antibiotics without drainage fail because drugs do not penetrate pus; when the story is 'three courses and it keeps coming back', the answer is usually a blade, not a fourth course.
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