An epidermal inclusion cyst is a benign sac under the skin, lined by epidermis and filled with keratin, a soft, cheesy material. It forms when surface skin cells get trapped deeper, often in a hair follicle, and is most common on the face, neck and trunk.
Key symptoms
- Slow-growing, round lump under the skin
- Usually painless
- Cheesy, foul-smelling material may leak out
- Sudden pain, redness and swelling if it ruptures or gets inflamed
What you find on exam
- Firm, mobile, dome-shaped nodule 0.5 to 5 cm across
- Small dark central pore (punctum)
- Inflamed cyst: red, warm, tender and sometimes fluctuant
- Check for spreading redness around it
Tests
- Clinical diagnosis
- Ultrasound if the lump is deep or the diagnosis is unclear
- Pathology of the removed cyst if atypical; culture any pus if infection is suspected
Treatment basics
- No treatment needed if it causes no problems
- Complete surgical excision of the cyst wall once it is calm, to prevent recurrence
- Inflamed but not infected: warm compresses or intralesional triamcinolone
- Fluctuant abscess: incision and drainage; antibiotics only if there is surrounding cellulitis
Red flags
- Spreading redness, fever or signs of sepsis
- Rapid growth, a hard fixed mass or ulceration
- Many cysts in a young person (consider Gardner syndrome)
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Sources: NCCPA PANCE Content Blueprint; NBOME COMLEX-USA clinical presentations; AAMC Core Entrustable Professional Activities (Core EPAs). Written by Making Synapses. Making Synapses is not affiliated with these organizations.