# Epidermoid cyst
An **epidermoid cyst** is a benign, slow-growing lump under the skin, derived from the infundibulum (upper portion) of a hair follicle and encapsulated in a thin layer of epidermis-like epithelium, typically filled with keratin and lipid-rich debris[1](https://dermnetnz.org/topics/epidermoid-cyst). It is also called an epidermal cyst, epidermal inclusion cyst, follicular infundibular cyst, infundibular cyst, keratin cyst, or epithelial cyst[1](https://dermnetnz.org/topics/epidermoid-cyst) • [2](https://medlineplus.gov/ency/article/000842.htm). The name "sebaceous cyst" is a common misnomer: these cysts do not involve sebaceous glands and do not contain sebum, while a true sebaceous cyst, filled with yellowish oily material, is called a steatocystoma[1](https://dermnetnz.org/topics/epidermoid-cyst) • [2](https://medlineplus.gov/ency/article/000842.htm).
| Key fact | Detail |
|---|---|
| Definition | Benign cyst from the hair follicle infundibulum, lined by epidermis-like stratified squamous epithelium and filled with keratin[1](https://dermnetnz.org/topics/epidermoid-cyst) |
| Typical appearance | Firm, flesh-colored or yellowish round nodule, 1–3 cm in diameter, fixed to the skin surface but mobile over deeper layers, often with a central punctum[1](https://dermnetnz.org/topics/epidermoid-cyst) |
| Common sites | Central trunk (chest, shoulders) and face; also common on the scrotum and vulva[1](https://dermnetnz.org/topics/epidermoid-cyst) |
| Who gets them | Most common in young-to-middle-aged adults; occur twice as frequently in men as in women[1](https://dermnetnz.org/topics/epidermoid-cyst) |
| Diagnosis | Usually made clinically; ultrasound sensitivity 80.0% and specificity 95.4% when imaging is needed[1](https://dermnetnz.org/topics/epidermoid-cyst) • [3](https://doi.org/10.2214/AJR.13.11457) |
| Definitive treatment | Complete surgical excision with an intact cyst capsule; removal of the entire lining decreases recurrence[1](https://dermnetnz.org/topics/epidermoid-cyst) |
| Malignancy | Very rare; in a 15-year review of 13,746 excised cysts, 48 specimens (0.3%) showed malignancy, most commonly squamous cell carcinoma[4](https://pubmed.ncbi.nlm.nih.gov/27070686/) |
## Causes
An epidermoid cyst generally results from an occluded pilosebaceous unit, the structure containing the hair follicle and its associated glands[1](https://dermnetnz.org/topics/epidermoid-cyst). On non-hair-bearing areas such as the buttock, palm of the hand, or sole of the foot, a cyst may instead arise from traumatic implantation of epidermal cells into the dermis, where keratin accumulates within an epithelium-lined sac[1](https://dermnetnz.org/topics/epidermoid-cyst). MedlinePlus describes the same process in plain terms: elements of the surface skin get beneath the skin surface, and the enclosed skin cells keep growing without being shed, filling the sac with dead skin until the cyst reaches a certain size and usually stops growing[2](https://medlineplus.gov/ency/article/000842.htm).
Multiple epidermoid cysts can be a cutaneous sign of genetic disorders including Gardner syndrome, pachyonychia congenita type 2, and basal cell naevus syndrome[1](https://dermnetnz.org/topics/epidermoid-cyst). Early-onset cysts or cysts at unusual sites such as the limbs may be a clue to autosomal dominant Gardner syndrome, a condition associated with colorectal polyps that carry a high risk of malignant development[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC6732711/).
## Clinical features
The typical lesion is a firm, flesh-colored or yellowish round papule or nodule, 1–3 cm in diameter, fixed to the skin surface but usually mobile over deeper tissue, with a central punctum (a small pore) through which foul-smelling, cheesy debris can sometimes be expressed[1](https://dermnetnz.org/topics/epidermoid-cyst). Cysts are most common on the central trunk and face but occur almost anywhere on the body, are common on the scrotum and vulva, and may be solitary or multiple; they are generally asymptomatic[1](https://dermnetnz.org/topics/epidermoid-cyst). Scrotal and vulval cysts are frequently multiple and may calcify[6](https://dermnetnz.org/topics/cutaneous-cysts-and-pseudocysts).
## Complications
**Rupture and inflammation.** When cyst contents spill into the dermis, the keratin acts as a foreign material and triggers swelling, redness, and tenderness; histologically, exposed keratin elicits a neutrophilic and then granulomatous reaction[1](https://dermnetnz.org/topics/epidermoid-cyst) • [7](https://dermnetnz.org/topics/epidermoid-cyst-pathology). Rupture can follow trauma or bacterial infection, commonly by *Staphylococcus aureus*, *Escherichia coli*, or group A streptococcus[1](https://dermnetnz.org/topics/epidermoid-cyst). An infected cyst can form a painful abscess[2](https://medlineplus.gov/ency/article/000842.htm).
**Surgical complications and recurrence.** Excision can lead to bleeding, secondary bacterial infection, and scarring, and a cyst may recur if it has ruptured or if the capsule is not removed in its entirety[1](https://dermnetnz.org/topics/epidermoid-cyst).
**Malignant change.** Cutaneous squamous cell carcinoma may very rarely arise within an epidermoid cyst[1](https://dermnetnz.org/topics/epidermoid-cyst). In a 15-year single-institution review of 13,746 excised specimens labeled as sebaceous-type cysts, 48 (0.3%) had a histopathologic diagnosis of malignancy, most commonly squamous cell carcinoma, and in every such case the surgeon had reported diagnostic uncertainty from the history or physical characteristics[4](https://pubmed.ncbi.nlm.nih.gov/27070686/). A retrospective review of 202 excised suspected epidermoid and pilar cysts found malignancy in one case (basal cell carcinoma) and premalignancy in another (keratoacanthoma) among 36 cases misdiagnosed at operation[8](https://academic.oup.com/bjs/article/110/Supplement_7/znad258.066/7254078).
## Diagnosis
The diagnosis is usually made clinically by examining the skin[1](https://dermnetnz.org/topics/epidermoid-cyst) • [2](https://medlineplus.gov/ency/article/000842.htm). Biopsy is usually not required, but histological examination of an excised specimen is recommended because of the small risk of malignant transformation and misdiagnosis[1](https://dermnetnz.org/topics/epidermoid-cyst). Characteristic histological features are a unilocular (single-cavity) cystic structure in the dermis, lined by stratified squamous epithelium resembling epidermis, with a granular layer containing keratinohyaline granules and lamellated keratin in the lumen, and lacking the rete ridges seen in the overlying epidermis[1](https://dermnetnz.org/topics/epidermoid-cyst) • [7](https://dermnetnz.org/topics/epidermoid-cyst-pathology).
Although ultrasound may help when first assessing a soft tissue mass, a routine cyst typically does not need this imaging.[1](https://dermnetnz.org/topics/epidermoid-cyst) Reported ultrasound performance for epidermoid cysts includes sensitivity of 80.0% and specificity of 95.4%[3](https://doi.org/10.2214/AJR.13.11457). In a 2023 study of high-frequency ultrasound (HFUS) for subcutaneous lesions, adding HFUS to clinical examination improved diagnostic accuracy for epidermoid cysts from 59.6% to 86.7%, and reduced the overall indeterminate diagnosis rate from 36.6% to 2.6%[9](https://onlinelibrary.wiley.com/doi/10.1111/srt.13464).
## Differential diagnosis
Conditions that can resemble an epidermoid cyst include[1](https://dermnetnz.org/topics/epidermoid-cyst) • [5](https://pmc.ncbi.nlm.nih.gov/articles/PMC6732711/):
- **Lipoma**, a mobile 2–10 cm dome- or egg-shaped subcutaneous lump with a rubbery or soft, smooth consistency
- **Trichilemmal (pilar) cyst**, a firm, mobile 0.5–5 cm nodule without a central punctum, usually on the scalp, with a thick capsule and not typically prone to rupture
- **Dermoid cyst**, which contains epidermal and dermal components such as hair follicles and sweat glands and arises in early childhood; the absence of skin adnexal structures in the wall is the key histological feature distinguishing an epidermoid cyst from a dermoid cyst[10](https://www.cureus.com/articles/409241-epidermal-inclusion-cysts-of-the-head-and-neck-a-one-year-tertiary-care-experience-with-emphasis-on-the-periauricular-region-and-review-of-literature.pdf)
- **Acne pseudocyst**, which lacks a capsule and occurs with other signs of acne
- **HPV-related epidermal cyst**, a lesion with a hard, keratinous surface
- Cystic basal cell carcinoma and other [cutaneous cysts](https://www.edgepedia.org/cutaneous-cysts) such as milia, branchial cleft cyst, and pilonidal cyst
## Treatment
Most small, uncomplicated epidermoid cysts do not require treatment[1](https://dermnetnz.org/topics/epidermoid-cyst) • [2](https://medlineplus.gov/ency/article/000842.htm). The most effective treatment is complete surgical excision with an intact cyst capsule; removing the entire cyst lining decreases recurrence rates, though this is difficult to achieve after the cyst has ruptured[1](https://dermnetnz.org/topics/epidermoid-cyst). Surgery is best avoided while the cyst is actively inflamed because of a higher risk of infection, wound dehiscence, and recurrence[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC6732711/).
For inflamed or infected cysts, options include incision and drainage, which the 2014 Infectious Diseases Society of America guidelines recommend for inflamed epidermoid cysts (strong recommendation, high-quality evidence), oral antibiotics for infection, or steroid injection for an inflamed, swollen cyst[11](https://academic.oup.com/cid/article/59/2/e10/2895845) • [2](https://medlineplus.gov/ency/article/000842.htm). A warm moist compress over the area may help an inflamed cyst drain and heal[2](https://medlineplus.gov/ency/article/000842.htm).
## Outcome
Epidermoid cysts are typically benign and slow growing, rarely undergoing malignant transformation, and occasionally resolve spontaneously without intervention[1](https://dermnetnz.org/topics/epidermoid-cyst). They may return if not completely removed by surgery[2](https://medlineplus.gov/ency/article/000842.htm).
## References
1. [Epidermoid cyst, DermNet NZ](https://dermnetnz.org/topics/epidermoid-cyst)
2. [Epidermoid cyst, MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000842.htm)
3. [Ultrasound of Musculoskeletal Soft-Tissue Tumors Superficial to the Investing Fascia, AJR](https://doi.org/10.2214/AJR.13.11457)
4. [Is Routine Pathologic Evaluation of Sebaceous Cysts Necessary? A 15-Year Retrospective Review, Annals of Plastic Surgery](https://pubmed.ncbi.nlm.nih.gov/27070686/)
5. [Overview of epidermoid cyst, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC6732711/)
6. [Cutaneous cysts and pseudocysts, DermNet NZ](https://dermnetnz.org/topics/cutaneous-cysts-and-pseudocysts)
7. [Epidermoid cyst pathology, DermNet NZ](https://dermnetnz.org/topics/epidermoid-cyst-pathology)
8. [Should All Excised Suspected Epidermoid and Pilar Cysts Undergo Histological Analysis? BJS](https://academic.oup.com/bjs/article/110/Supplement_7/znad258.066/7254078)
9. [Diagnostic value of high-frequency ultrasound (HFUS) in evaluation of subcutaneous lesions, Skin Research and Technology](https://onlinelibrary.wiley.com/doi/10.1111/srt.13464)
10. [Epidermal Inclusion Cysts of the Head and Neck, Cureus](https://www.cureus.com/articles/409241-epidermal-inclusion-cysts-of-the-head-and-neck-a-one-year-tertiary-care-experience-with-emphasis-on-the-periauricular-region-and-review-of-literature.pdf)
11. [Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections: 2014 Update, IDSA, Clinical Infectious Diseases](https://academic.oup.com/cid/article/59/2/e10/2895845)
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*Topic: Encyclopedia › Life and health › Human health and medicine › Diseases and injuries › Skin and musculoskeletal conditions*
*Initially written Sep 17, 2026 · Reviewed: Oct 21, 2026 · Edited: Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
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