epidermoid cyst forms when epidermal cells become trapped below the skin surface, creating a “keratin sac” — the sac is filled with a mixture of keratin and sebum (often with a stinky-tofu smell).core feature: an intact capsule. Squeezing out the contents without removing the capsule leaves the sac in place; it keeps producing new keratin → repeated swelling → repeated inflammation → larger and more scarred over time. The notion that "epidermoid cyst = acne pimple" is incorrect.
What is an Epidermoid Cyst?
An epidermoid cyst (also called epidermal inclusion cyst, sebaceous cyst — though "sebaceous" is technically inaccurate) is a benign skin cyst formed when epidermal cells become trapped in the dermis and continue to produce keratin. Result: a sac (cyst wall) filled with cheesy keratin debris. They commonly appear on face, neck, trunk, scrotum.
Cyst vs Acne — Critical Distinction
| Epidermoid cyst | Cystic acne / inflamed acne nodule | |
|---|---|---|
| Cause | Trapped epidermal sac with keratin | Sebaceous gland inflammation, bacterial |
| Course | Long-term existing nodule (years), enlarges slowly | Rapid onset over days; resolves in 1-3 weeks |
| Punctum (central pore) | Visible black/dark spot | None |
| Content | White-yellow cheesy keratin (foul-smelling) | Pus or sterile inflammatory exudate |
| Treatment | Surgical excision (only definitive cure) | Topical/systemic antibiotic, isotretinoin |
| Recurrence after treatment | Rare if cyst wall fully removed | Yes, may flare again |
Key teaching: an "acne pimple" that has existed for > 6 months and slowly enlarged is almost certainly NOT acne — likely an epidermoid cyst. Same nodule recurring at the same spot every few months is also classic.
Why You Shouldn't Squeeze It
Many people think "squeezing makes it disappear." It doesn't — and creates problems:
- Squeezing only releases content, NOT the cyst wall — the wall remains and fills with keratin again
- High infection risk: introduced bacteria → cellulitis or abscess. ~15-20% of squeezed cysts develop frank infection requiring antibiotics + I&D
- Inflammation makes future surgery harder: scar tissue obscures cyst boundaries, lowering complete-removal success
- Increased scarring: post-inflammatory pigmentation + tissue distortion
When to Treat?
Indications:
- Cosmetically bothersome (face, exposed areas)
- Mechanical irritation (clothing rubbing, glasses, bra strap)
- Recurrent infection
- Continuing to enlarge
- Diagnostic uncertainty (need biopsy to rule out other lesions)
Asymptomatic small cysts that don't bother the patient can be observed.
Treatment Options
Inflamed phase (red, painful, fluctuant)
- NOT the time for elective excision — wait until inflammation resolves (~4-6 weeks)
- Intralesional triamcinolone (5-10 mg/mL): rapid anti-inflammation
- Oral antibiotic (cephalexin, dicloxacillin) if infection signs (cellulitis, fever)
- Incision & drainage (I&D) if abscessed: relieves pressure and pain; cyst wall remains, will recur — plan elective excision later
Quiet phase — definitive surgery
- Elliptical excision (gold standard): elliptical incision encompassing the cyst + punctum; remove cyst wall en bloc; primary closure with sutures. Recurrence rate < 5% if wall fully removed
- Minimal excision technique: small (3-4 mm) incision over cyst, manual extrusion of contents, then careful dissection and removal of wall. Smaller scar, slightly higher recurrence (~5-10%) if wall remnant left
- Punch biopsy approach: 3-4 mm punch over punctum, extrude contents, grasp and remove wall. Suitable for small cysts
- CO₂ laser: vaporize wall after content removal — alternative for cosmetically sensitive areas
NHI Coverage
Taiwan NHI covers cyst excision under "benign skin tumor excision" (procedure code varies by site / size). Most cases can be done in outpatient under local anesthesia (~30 min). Multiple cyst removal in one session may bundle.
Post-op Care
- Keep dressing dry × 24-48 hours
- Suture removal at 7-10 days (face) or 10-14 days (trunk / extremities)
- Watch for: increasing redness, swelling, drainage (signs of infection)
- Sun protection over scar × 6 months to minimize PIH
- Silicone gel / sheet on scar from week 2-4 to optimize cosmesis
Summary
Epidermoid cysts are common and benign — but they don't go away on their own and cannot be "popped" away. Surgical excision is the definitive cure. Resist squeezing, schedule excision when quiet, and the lesion is gone for good with a small scar.