A skin cyst is a closed pocket under the skin. The most common kind is the epidermoid cyst, also known as an epidermal inclusion cyst or a follicular infundibular cyst. It is often called a sebaceous cyst, though that name is not accurate. It is filled with keratin and dead skin cells. These cysts are very common, most often appear between the ages of 20 and 60, and affect men about twice as often as women. Most are harmless and many never need treatment.
What a cyst looks like
An epidermoid cyst is a round, firm, dome-shaped bump that moves under the skin. It is usually painless and grows slowly, often stopping at a certain size. Some have a small dark pit in the center. They are most common on the face, neck, chest, shoulders and back, and range from about a quarter inch to more than 2 inches across.
A pilar cyst is another type. About 90% grow on the scalp. They have no central pit, are more often found in middle-aged women, and tend to run in families. Milia are another type of skin cyst.
Why cysts form
An epidermoid cyst forms when skin cells end up under the surface instead of shedding, often because a hair follicle is blocked. An injury, acne or long-term sun damage can set this off, and cysts can run in families. They are not contagious.
When to see a dermatologist
Have any new lump looked at, because a few skin cancers can look like a cyst at first. See a dermatologist sooner if a cyst:
- turns red, warm, swollen or painful
- drains pus or a cheesy, foul-smelling material
- grows quickly, or grows larger than about 5 cm
A cyst that ruptures under the skin can become inflamed and infected, and an infected cyst can form a painful abscess.
Do not squeeze, pop or cut a cyst open yourself. It can cause infection, and the cyst will likely return because its lining is still there. A warm, moist cloth may help a mildly inflamed cyst settle while you wait for an appointment.
What a visit involves
Most cysts are diagnosed by looking at and feeling them. If anything about the lump is unusual, the dermatologist may take a biopsy, and occasionally imaging is used. If infection is suspected, a skin culture may be taken.
How dermatologists treat cysts
Treatment depends on whether the cyst is quiet or inflamed.
- Leaving it alone. A small cyst that causes no trouble can simply be watched.
- Calming an inflamed cyst. A steroid injection into the cyst, or incision and drainage, can bring down swelling. Some cysts are inflamed rather than infected, and incision and drainage may help resolve the inflammation. An infected cyst may need antibiotics by mouth.
- Drainage. A small cut lets the contents out and relieves the swelling. It does not remove the lining, so the cyst often refills.
- Removal. Under a local anesthetic, the whole cyst is taken out with its sac and the skin is closed with stitches. This is the treatment that makes a return unlikely. An infected cyst may need to be treated first, with a planned removal saved for once the infection has resolved.
What to expect afterwards
A small cyst removed without stitches usually heals in a few days to a couple of weeks. A larger one can take several weeks or longer. Stitches are usually checked or removed about 7 to 10 days later. Infection, bleeding and scarring are uncommon risks. Fever, pus, a bad smell from the wound or severe pain are reasons to call the office.
How to choose a dermatologist
Ask how often they remove cysts and whether they plan to remove the whole sac or drain it. Ask what they do if the cyst is inflamed on the day of your visit. If you have insurance, ask whether a referral is needed and whether your plan treats the removal as medical or cosmetic, since that can change what you pay. Bring a note of how long the lump has been there and whether it has ever been red or drained.
The city list below shows dermatologists who name cysts on their own websites.