Furuncle

A furuncle is an acute purulent-necrotic inflammation of a single hair follicle, sebaceous gland, and the surrounding connective tissue. It is one of the most common forms of staphylococcal pyoderma (purulent skin infections).

Unlike more superficial inflammatory conditions such as folliculitis, a furuncle involves a deep purulent infiltrate and a central necrotic core. The condition when multiple or recurrent furuncles develop is referred to as furunculosis.

Aetiology and Pathophysiology

In over 90 % of cases, the primary causative agent is Staphylococcus aureus. Initially, the infection penetrates the hair follicle, where the bacteria begin to proliferate.

This triggers a robust inflammatory response. A firm, painful nodule then develops, with central necrosis of the follicle and adjacent tissue, forming a purulent-necrotic core. This core is a hallmark feature of a furuncle.

Clinical significance

A furuncle typically progresses through several stages. Initially, a painful red papule appears. The lesion enlarges, and a pustule forms at its apex. Within a few days, the furuncle “matures”, ruptures, and drains pus, followed by the expulsion of the necrotic core.

Uncomplicated solitary furuncles are usually treated conservatively. Warm compresses are applied to promote maturation and spontaneous drainage. Furuncles — especially on the face — must not be squeezed due to the risk of hematogenous spread of infection and potentially life-threatening complications such as cavernous sinus thrombosis or sepsis.

Larger lesions, signs of systemic toxicity, or involvement of high-risk anatomical areas require surgical incision and drainage, along with systemic antibiotic therapy.

Differential Diagnosis

It is essential to distinguish a furuncle from other purulent skin conditions:

• Carbuncle. A more severe condition involving inflammation of multiple adjacent hair follicles that coalesce into a single extensive lesion.

Folliculitis. A superficial inflammation limited to the hair follicle, without deep infiltration or a necrotic core.