Epidermal Cysts
Common, harmless lumps under the skin filled with keratin
Quick Facts
- Type: Benign skin cyst
- Filled with: Keratin (a skin protein)
- Common sites: Face, neck, trunk, back
- Nature: Harmless; may be removed if bothersome
Overview
Epidermal cysts are common, noncancerous lumps that develop under the skin. Each cyst is a closed sac lined with skin cells that fills with keratin, the soft, cheese-like protein that normally forms the outer layer of the skin. They are often called sebaceous cysts in everyday language, though that term is not entirely accurate because they do not arise from oil (sebaceous) glands.
These cysts most often appear on the face, neck, trunk, and back. They are usually painless and grow slowly. Most cause no problems and do not require treatment, but they can become inflamed, infected, or cosmetically bothersome, in which case a doctor can remove them. Epidermal cysts are closely related to the epidermoid cyst and the term sebaceous cyst, and similar to pilar cysts that form on the scalp.
Epidermal cysts are extremely common and usually nothing to worry about. Many people live with one for years without any trouble. The most frequent problems are cosmetic concern, or a cyst becoming inflamed or infected, which can make it red and painful. Understanding what these cysts are helps people avoid unnecessary worry and resist the urge to squeeze them, which often makes matters worse.
Symptoms
Epidermal cysts typically have these features:
- A round, firm lump under the skin that moves slightly
- A small dark dot (a blocked pore) sometimes visible on the surface
- Slow growth over weeks to years
- Usually painless unless inflamed or infected
- May leak a thick, foul-smelling, cheese-like material if it ruptures
- Sizes ranging from a small pea to several centimeters
If a cyst becomes red, swollen, tender, warm, or starts draining pus, it may be inflamed or infected and should be evaluated rather than squeezed.
Causes
Epidermal cysts form when surface skin cells, which normally shed, instead move deeper and multiply within a sac:
- Trapped skin cells: Cells that produce keratin become enclosed beneath the skin and continue to build up.
- Blocked or damaged hair follicles: Often related to the opening of a hair follicle.
- Skin injury: Minor trauma or surgery can push surface cells deeper.
- Genetic conditions: Rarely, numerous cysts are linked to inherited syndromes.
They are not caused by poor hygiene and are not contagious. The keratin inside is what gives a ruptured cyst its thick, pungent contents.
Risk Factors
- Being past puberty (more common in adults)
- A history of acne or skin injury
- Previous skin trauma or surgery at the site
- Certain rare inherited conditions
- More common in men than women
Diagnosis
Epidermal cysts are usually diagnosed by examination:
- Physical exam: A doctor can often identify the cyst by its appearance and feel, including the central pore.
- Imaging: Occasionally an ultrasound is used to confirm a fluid-filled cyst.
- Biopsy or pathology: If a cyst is removed or looks unusual, the tissue may be examined to confirm the diagnosis.
Most cysts are straightforward to recognize and do not need extensive testing.
Treatment
Many epidermal cysts need no treatment. Options when treatment is wanted include:
- Observation: Leaving a small, painless cyst alone if it is not bothersome.
- Surgical removal: A doctor removes the entire cyst sac, which is the best way to prevent it from returning.
- Treating inflammation or infection: An inflamed cyst may be drained, and antibiotics or a steroid injection may be used; full removal is usually done later once the inflammation settles.
It is best not to squeeze or pop a cyst at home, since this can cause infection, scarring, and recurrence.
Self-Care
- Avoid squeezing, picking, or trying to pop the cyst
- Keep the area clean to reduce the chance of infection
- Apply a warm compress if a cyst is mildly inflamed, then seek care
- See a doctor for removal if a cyst is growing, bothersome, or recurring
- Watch for signs of infection such as redness, warmth, and pain
When to See a Doctor
See a doctor if a cyst becomes painful, red, swollen, or starts draining, grows quickly, or keeps coming back, or if you simply want it removed. Have any new, rapidly enlarging, or unusual lump evaluated to confirm it is benign. Seek prompt care for spreading redness, fever, or significant pain, which can indicate a spreading skin infection that needs treatment.
Frequently Asked Questions
Are epidermal cysts cancerous?
No, epidermal cysts are benign and very rarely become cancerous. They are harmless sacs filled with keratin, a normal skin protein. Any lump that grows rapidly, looks unusual, or behaves differently should still be checked by a doctor to be sure.
What is inside an epidermal cyst?
An epidermal cyst contains keratin, the protein that forms the outer layer of skin. When a cyst ruptures, this keratin can come out as a thick, pale, cheese-like material with a foul smell. It is not pus unless the cyst is also infected.
Should I pop an epidermal cyst?
No. Squeezing or popping a cyst can push contents deeper, cause infection, lead to scarring, and make it more likely to come back. If a cyst bothers you, a doctor can remove the whole sac safely, which gives the best chance of it not returning.
Why did my cyst become red and painful?
A previously quiet cyst can become inflamed or infected, causing redness, swelling, warmth, and tenderness. This may happen if it ruptures under the skin or bacteria get in. See a doctor, who may drain it, prescribe antibiotics, or plan removal once it settles.
Do epidermal cysts go away on their own?
Some small cysts stay stable or occasionally shrink, but most do not fully disappear on their own. They often remain the same or slowly grow. The only reliable way to remove a bothersome cyst permanently is surgical removal of the entire sac.
References
- American Academy of Dermatology (AAD). Cysts: Overview.
- Mayo Clinic. Epidermoid cysts.
- MedlinePlus, U.S. National Library of Medicine. Epidermoid (sebaceous) cyst.
- DermNet. Epidermoid cyst.