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.
• 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 or iron-deficiency anaemia.
• Immunosuppression (illness or drugs such as corticosteroids).
• Atopic eczema or other skin disease.
• Smoking.
• 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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