furuncle

A furuncle, commonly called a boil, is a deep-seated infection of a hair follicle and surrounding dermis. It is usually caused by Staphylococcus aureus and often begins with folliculitis that progresses to an abscess. Furuncles are most frequent on the neck, face, armpits, buttocks, and thighs and are more common in adults and people with skin trauma or conditions that affect immunity.

Clinical features include a tender, erythematous nodule that enlarges and becomes fluctuant with a central pus-filled head. The lesion is typically painful and may be accompanied by fever or malaise if the infection is extensive. Diagnosis is clinical; cultures may be considered for recurrent or severe cases, or to guide antibiotic choices.

Management depends on the stage and extent. Fluctuant furuncles require incision and drainage (I&D) as first-line treatment; warm compresses may help small lesions. Antibiotics are not routinely needed after I&D but are indicated for extensive surrounding cellulitis, systemic signs, immunocompromise, or multiple concurrent furuncles. When antibiotics are used, agents effective against Staphylococcus aureus are chosen (for MSSA: cephalexin or dicloxacillin; for MRSA: trimethoprim–sulfamethoxazole, doxycycline, or clindamycin). Avoid squeezing or rupturing the lesion and keep it clean.

Recurrent furuncles may reflect nasal carriage of S. aureus; decolonization and hygiene measures can reduce recurrence. Potential complications include cellulitis, abscess formation, scarring, and, rarely, bacteremia or septicemia.