Incision and drainage of a skin abscess

What it is

A skin abscess is a walled-off collection of pus in the dermis or subcutaneous tissue, most often caused by Staphylococcus aureus, including methicillin-resistant strains. It is a red, warm, tender swelling that becomes fluctuant; a furuncle starts in a hair follicle and a carbuncle is several joined furuncles. Antibiotics penetrate the cavity poorly, so incision and drainage (I&D) is the definitive treatment. When it is unclear whether there is pus, point-of-care ultrasound shows a hypoechoic or anechoic collection, sometimes with swirling debris, while cellulitis alone shows a cobblestone pattern without a cavity. The incision is linear, follows the skin tension lines, lies over the most fluctuant point and is long enough to drain the whole cavity; loculations are broken with a blunt instrument and the cavity is irrigated. Packing is no longer routine for small abscesses, and loop drainage through two small incisions is an alternative that leaves smaller scars. Antibiotics are added when there is systemic illness, extensive cellulitis, immunosuppression, a site that is hard to drain or failure of drainage alone. Some abscesses belong to the surgeon: those of the perianal region, the central face, the hand, the breast and deep spaces.

Indications

• Fluctuant skin abscess, furuncle or carbuncle.
• Collection confirmed by ultrasound when the swelling is indurated but not clearly fluctuant.
• Abscess that has not responded to warm compresses and is enlarging or painful.
• Infected epidermoid cyst with a collection (definitive excision of the cyst wall comes later).
• Obtaining pus for culture in recurrent, severe or treatment-resistant infections.

Contraindications and precautions

• Refer to surgery: perianal and perirectal abscesses, which may extend deep or form a fistula.
• Refer: hand and finger abscesses (tendon sheaths and deep spaces), central-face abscesses (venous spread to the cavernous sinus), and deep neck abscesses.
• Breast abscess: needle aspiration under ultrasound is often tried first, especially during lactation.
• Possible pseudoaneurysm or vascular malformation, mostly in the groin, neck or antecubital fossa of people who inject drugs: image first.
• Necrotising infection (pain out of proportion, crepitus, bullae, rapid spread, systemic toxicity): urgent surgery, not bedside I&D.

Equipment

• Gloves, eye protection, antiseptic solution, sterile drape and gauze.
• Local anaesthetic with a fine needle for a field block around the abscess.
• Scalpel with a pointed blade (No. 11) and a curved haemostat to break loculations.
• Syringe and saline for irrigation, a swab or sterile tube for culture.
• Gauze strip for packing if needed, or two small incisions and a soft loop for loop drainage; absorbent dressing; ultrasound if available.

Step by step (and why)

1. Confirm pus by fluctuance or ultrasound, exclude a vascular lesion and consent — cutting cellulitis or a pseudoaneurysm causes harm.
2. Clean the skin and drape — keeping the field clean lowers secondary infection and protects you from splashes.
3. Inject a field block around and under the abscess, not into it — acidic pus weakens the anaesthetic and the cavity is under pressure.
4. Incise linearly along skin lines over the most fluctuant point, across the cavity — a long enough incision avoids early closure.
5. Let the pus drain, express gently and send a sample for culture when indicated — culture guides treatment in recurrent or severe cases.
6. Break all loculations with a curved haemostat — trapped pockets are a common cause of failure.
7. Irrigate the cavity with saline until the return is clear — irrigation removes residual pus and debris.
8. Pack loosely or place a loop only for large or deep cavities, then dress — packing keeps the incision open but adds pain.

Complications

• Incomplete drainage and recurrence, usually from a small incision or missed loculations.
• Spreading cellulitis, lymphangitis or bacteraemia after manipulation.
• Bleeding, particularly with anticoagulation or an unrecognised vascular lesion.
• Injury to nearby nerves, vessels or tendons in thin-skinned or anatomically complex areas.
• Pain during packing changes, scarring and, rarely, a chronic sinus.

Next step

• Review in 24–48 hours: remove or change any packing and check that redness and swelling are improving.
• Prescribe antibiotics covering methicillin-resistant S. aureus according to local resistance when there is systemic illness, extensive cellulitis or immunosuppression.
• Call a senior or surgeon for fever, rapid spread, signs of necrotising infection or an abscess that recurs after drainage.
• In recurrent abscesses look for diabetes, hidradenitis suppurativa and staphylococcal carriage, and consider decolonisation per protocol.
• Teach wound care: keep it covered, wash hands, do not share towels, and return with fever, spreading redness or new swelling.

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Elsewhere in DurgiPedia

• Skin examination: primary and secondary lesions
• Skin infections: the biopsy
• Wound care and dressings: cleaning and choosing a dressing
• Clean and sterile technique: medical and surgical asepsis

Connections

← All clinical skills

Educational content; it does not replace supervised hands-on training, your institution's protocols or a prescriber's order. A procedure is learnt with a teacher and done only once you are trained to do it.

Sources: Incision and Drainage (StatPearls (NCBI Bookshelf), 2023).

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