GPAtlas🧭 When to suspect
A boil (furuncle) is a deep bacterial infection of a single hair follicle that forms a small abscess; a carbuncle is a deeper, interconnected cluster of infected follicles draining through several points. Both sit on a spectrum with simple folliculitis and are usually caused by Staphylococcus aureus. Suspect a boil when there is a painful, firm, red nodule in a hair-bearing, friction-prone area (neck, axilla, buttock, thigh) that enlarges over days and becomes fluctuant; suspect a carbuncle when the lesion is larger, indurated and discharging from multiple sinuses, often with systemic upset.
The two clinical priorities in primary care are to recognise when drainage rather than an antibiotic is the answer, and to identify the minority who need escalation – the systemically unwell, the immunocompromised, the central-face lesion, and the patient with recurrent or clustered boils suggesting PVL-producing S. aureus.
| Lesion | What it is | Typical features |
|---|---|---|
| Folliculitis | Superficial inflammation or infection of a hair follicle | Small papules and pustules, often pierced by a central hair; usually mild and self-limiting |
| Furuncle (boil) | A deeper follicular infection forming a small abscess | Firm, tender, red nodule that enlarges, becomes fluctuant and points; discharges pus and a necrotic core |
| Carbuncle | Coalescence of several adjacent infected follicles | Larger, deeper, indurated mass (classically nape of neck or back) with multiple draining sinuses; systemic upset more likely |
Risk is higher with diabetes, obesity, iron-deficiency anaemia, immunosuppression (illness or drugs such as corticosteroids), atopic eczema or other skin disease, smoking, and nasal or perineal staphylococcal carriage. Transmission is favoured by skin-to-skin contact, shared towels or razors, and close communities such as households and contact-sports teams.
Source: DermNet
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