Furunculosis

BASICS

DESCRIPTION

Acute bacterial abscess of a hair follicle (often Staphylococcus aureus)
System(s) affected: skin/exocrine
Synonym(s): boils

EPIDEMIOLOGY

Incidence

Predominant age
- Adolescents and young adults
- Clusters have been reported in teenagers living in crowded quarters, within families, or in high school athletes.
Predominant sex: male = female

Prevalence

Exact data are not available.

ETIOLOGY AND PATHOPHYSIOLOGY

Infection spreads away from hair follicle into surrounding dermis.
Pathogenic strain of S. aureus (usually); most cases in United States are now due to community-acquired methicillin-resistant S. aureus (CA-MRSA), whereas methicillin-sensitive S. aureus (MSSA) is most common elsewhere (1)[A].

Genetics

Unknown

RISK FACTORS

Carriage of pathogenic strain of Staphylococcus sp. in nares, skin, axilla, and perineum
Rarely, polymorphonuclear leukocyte defect or hyperimmunoglobulin E–Staphylococcus sp. abscess syndrome
Diabetes mellitus, malnutrition, alcoholism, obesity, atopic dermatitis
Primary immunodeficiency disease and AIDS (common variable immunodeficiency, chronic granulomatous disease, Chédiak–Higashi syndrome, C3 deficiency, C3 hypercatabolism, transient hypogammaglobulinemia of infancy, immunodeficiency with thymoma, Wiskott-Aldrich syndrome)
Secondary immunodeficiency (e.g., leukemia, leukopenia, neutropenia, therapeutic immunosuppression)
Medication impairing neutrophil function (e.g., omeprazole)
The most important independent predictor of recurrence is a positive family history.

GENERAL PREVENTION

Patient education regarding self-care (see “General Measures”); treatment and prevention are interrelated.

COMMONLY ASSOCIATED CONDITIONS

Usually normal immune system
Diabetes mellitus
Polymorphonuclear leukocyte defect (rare)
Hyperimmunoglobulin E–Staphylococcus sp. abscess syndrome (rare)
See “Risk Factors.”

DIAGNOSIS

HISTORY

Located on hair-bearing sites, especially areas prone to friction or repeated minor traumas (e.g., underneath belt, anterior aspects of thighs, nape, buttocks)
No initial fever or systemic symptoms
The folliculocentric nodule may enlarge, become painful, and develop into an abscess (frequently with spontaneous drainage).

PHYSICAL EXAM

Painful erythematous papules/nodules (1 to 5 cm) with central pustules
Tender, red, perifollicular swelling, terminating in discharge of pus and necrotic plug
Lesions may be solitary or clustered.

DIFFERENTIAL DIAGNOSIS

Folliculitis
Pseudofolliculitis
Carbuncles
Ruptured epidermal cyst
Myiasis (larva of botfly/tumbu fly)
Hidradenitis suppurativa
Atypical bacterial or fungal infections

DIAGNOSTIC TESTS & INTERPRETATION

Initial Tests (lab, imaging)

Obtain culture if with multiple abscesses marked by surrounding inflammation, cellulitis, systemic symptoms such as fever, or if immunocompromised.

Follow-Up Tests & Special Considerations

Immunoglobulin levels in rare (e.g., recurrent or otherwise inexplicable) cases
If culture grows gram-negative bacteria or fungus, consider polymorphonuclear neutrophil leukocyte functional defect.

Test Interpretation

Histopathology (although a biopsy is rarely needed)

Perifollicular necrosis containing fibrinoid material and neutrophils
At deep end of necrotic plug, in SC tissue, is a large abscess with a Gram stain positive for small collections of S. aureus.

TREATMENT

GENERAL MEASURES

Moist, warm compresses (provide comfort, encourage localization/pointing/drainage) 30 minutes QID
If pointing or large, incise and drain: Consider packing if large or incompletely drained.
Routine culture is not necessary for localized abscess in nondiabetic patients with normal immune system.
Sanitary practices: Change towels, washcloths, and sheets daily; clean shaving instruments; avoid nose picking; change wound dressings frequently; do not share items of personal hygiene (2)[B].

MEDICATION

First Line

Systemic antibiotics usually unnecessary, unless extensive surrounding cellulitis or fever. Other indications include a single abscess >2 cm, immunocompromise.
If suspecting MRSA, see “Second Line.”
If multiple abscesses, lesions with marked surrounding inflammation, cellulitis, systemic symptoms such as fever, or if immunocompromised: Place on antibiotic therapy directed at S. aureus for 10 to 14 days.
- Dicloxacillin (Dynapen, Pathocil) 500 mg PO QID or cephalexin 500 mg PO QID or clindamycin 300 mg TID, if penicillin-allergic

Second Line

Resistant strains of S. aureus (MRSA): clindamycin 300 mg q6h or doxycycline 100 mg q12h or trimethoprim-sulfamethoxazole (TMP-SMX DS) 1 tab q8–12h or minocycline 100 mg q12h
If known or suspected impaired neutrophil function (e.g., impaired chemotaxis, phagocytosis, superoxide generation), add vitamin C 1,000 mg/day for 4 to 6 weeks (prevents oxidation of neutrophils).
If antibiotic regimens fail:
- May try PO pentoxifylline 400 mg TID for 2 to 6 months (inhibits neutrophil activation and adhesion)
- Contraindications: recent cerebral and/or retinal hemorrhage; intolerance to methylxanthines (e.g., caffeine, theophylline); allergy to the particular drug selected
- Precautions: prolonged prothrombin time (PT) and/or bleeding; if on warfarin, frequent monitoring of PT

ONGOING CARE

FOLLOW-UP RECOMMENDATIONS

Patient Monitoring

Instruct patient to see physician if compresses are unsuccessful.

DIET

Unrestricted

PROGNOSIS

Self-limited: usually drains pus spontaneously and will heal with or without scarring within several days
Recurrent/chronic: may last for months or years
If recurrent, usually related to chronic skin carriage of staphylococci (nares or on skin). Treatment goals are to decrease or eliminate pathogenic strain or suppress pathogenic strain.
- Culture nares, skin, axilla, and perineum (culture nares of family members)
- Mupirocin 2%: Apply to both nares BID for 5 days each month.
- Culture anterior nares every 3 months; if failure, retreat with mupirocin or consider clindamycin 150 mg/day for 3 months.
- Long-term efficacy of strategies to eliminate carrier state (decolonization) remains unclear.
Especially in recurrent cases, wash entire body and fingernails (with nailbrush) daily for 1 to 3 weeks with povidone-iodine (Betadine), chlorhexidine (Hibiclens), or hexachlorophene (pHisoHex soap), although all can cause dry skin.

COMPLICATIONS

Scarring
Bacteremia
Seeding (e.g., septal/valve defect, arthritic joint)

Figures

Figure 5-14
Furuncle. This patient has a painful, "pointing" furuncular nodule on his thigh.
Figure 5-15
Abscess. This patient has the follicular occlusion triad, which consists of hidradenitis suppurativa, acne conglobata, and dissecting cellulitis of the scalp. This walled-off lesion began as folliculitis that later became a furuncle and then an abscess. Note the older violaceous scars from previous furuncles and cystic acne lesions.

Authors

Zoltan Trizna, MD, PhD

REFERENCES

Lin H-S, Lin P-T, Tsai Y-S, et al. Interventions for bacterial folliculitis and boils (furuncles and carbuncles). Cochrane Database Syst Rev. 2021;2(2):CD013099. [PMID:33634465]
Fritz SA, Camins BC, Eisenstein KA, et al. Effectiveness of measures to eradicate Staphylococcus aureus carriage in patients with community-associated skin and soft-tissue infections: a randomized trial. Infect Control Hosp Epidemiol. 2011;32(9):872–880. [PMID:21828967]

ADDITIONAL READING

Balakirski G, Hischebeth G, Altengarten J, et al. Recurrent mucocutaneous infections caused by PVL-positive Staphylococcus aureus strains: a challenge in clinical practice. J Dtsch Dermatol Ges. 2020;18(4):315–322. [PMID:32196137]
Ibler KS, Kromann CB. Recurrent furunculosis—challenges and management: a review. Clin Cosmet Investig Dermatol. 2014;7:59–64. [PMID:24591845]
Nowicka D, Grywalska E. Staphylococcus aureus and host immunity in recurrent furunculosis. Dermatology. 2019;235(4):295–305. [PMID:30995649]

CODES

ICD10

L02.92 Furuncle, unspecified
L02.12 Furuncle of neck
L02.429 Furuncle of limb, unspecified
L02.32 Furuncle of buttock
L02.425 Furuncle of right lower limb
L02.422 Furuncle of left axilla
L02.426 Furuncle of left lower limb
L02.621 Furuncle of right foot
L02.424 Furuncle of left upper limb
L02.423 Furuncle of right upper limb
L02.229 Furuncle of trunk, unspecified
L02.222 Furuncle of back [any part, except buttock]
L02.02 Furuncle of face
L02.629 Furuncle of unspecified foot
L02.622 Furuncle of left foot
L02.821 Furuncle of head [any part, except face]
L02.221 Furuncle of abdominal wall
L02.225 Furuncle of perineum
L02.828 Furuncle of other sites
L02.529 Furuncle unspecified hand
L02.224 Furuncle of groin
L02.226 Furuncle of umbilicus
L02.421 Furuncle of right axilla
L02.223 Furuncle of chest wall
L02.522 Furuncle left hand
L02.521 Furuncle right hand

SNOMED

40603000 Furunculosis of skin AND/OR subcutaneous tissue (disorder)
47763005 Furuncle of neck (disorder)
60198007 Furuncle of axilla
12430003 Furuncle of buttock (disorder)
37396007 Furuncle of face
67272008 Furuncle of trunk (disorder)
90942002 Furuncle of thigh
2606006 Furuncle of perineum

CLINICAL PEARLS

Pathogens may be different in different localities. Keep up-to-date with the locality-specific epidemiology.
If few, furuncles/furunculosis do not need antibiotic treatment. If systemic symptoms (e.g., fever), cellulitis, or multiple lesions occur, oral antibiotic therapy is used.
Other treatments for MRSA include linezolid PO or IV and IV vancomycin.
Folliculitis, furunculosis, and carbuncles are parts of a spectrum of pyodermas.
Other causative organisms include aerobic (e.g., Escherichia coli, Pseudomonas aeruginosa, and Streptococcus faecalis), anaerobic (e.g., Bacteroides, Lactobacillus, and Peptostreptococcus), and Mycobacteria.
Decolonization (treatment of the nares with topical antibiotic) is only recommended if the colonization was confirmed by cultures because resistance is common and treatment is of uncertain efficacy.

Last Updated: 2026

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