A smooth, dome-shaped lump that moves under your fingers and grows over months is very often a harmless cyst. Learn how to recognize one, why squeezing it backfires, and which changes mean it should be examined.
What most people call a sebaceous cyst is usually an epidermoid cyst: a keratin-filled sac under the skin that grows slowly and is almost always benign. Many need no treatment at all. Squeezing one out rarely works and often causes infection — complete surgical removal of the sac is the only way to prevent it returning.
Epidermoid cysts form when surface skin cells get trapped beneath the skin — often via a blocked hair follicle or a small injury — and keep producing keratin inside a sac. The result is a firm-to-doughy, rounded lump, typically 0.5–5 cm, that sits just under the skin and often shows a tiny central dark opening (a punctum). True sebaceous cysts (steatocystomas) arising from oil glands are much rarer, but the everyday name has stuck.
They are most common on the face, neck, chest, back and scalp (where a similar lesion is called a pilar cyst), appear most often in adults, and can sit unchanged for years. The cheesy, sometimes odorous material inside is keratin — not pus — unless the cyst becomes inflamed or infected.
An uninflamed cyst that doesn't bother you can simply be left alone. Do not squeeze it: home squeezing almost never removes the sac, so the cyst refills, and forcing keratin into the surrounding tissue triggers painful inflammation and infection. If a cyst becomes red, swollen and tender, warm compresses several times a day ease discomfort; a clinician may drain an acutely infected cyst or prescribe antibiotics if the surrounding skin is infected.
Definitive treatment is minor surgery to remove the entire sac, ideally when the cyst is quiet rather than inflamed — removal during infection has a higher recurrence rate. Reasons people choose removal include recurrent infections, ongoing discharge, rapid growth, friction with clothing, or cosmetic concern. It's a short local-anesthetic procedure.
The cyst is a closed keratin-filled sac. Squeezing may eject some contents through the punctum, but the sac lining stays behind and simply refills over weeks. Worse, pressure ruptures the sac inward, spilling keratin into surrounding tissue — the immune system treats keratin as foreign material, producing the angry, painful, sometimes infected inflammation that finally sends people to a doctor. The kindest thing you can do for a quiet cyst is leave it alone; the definitive fix is complete excision of the sac by a professional.
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Typical clues are a smooth, mobile, slow-growing dome under the skin, often with a small central dark punctum. But lumps that are hard, fixed, fast-growing or ulcerated need a professional exam rather than self-diagnosis.
No. Squeezing leaves the sac behind so the cyst refills, and it commonly ruptures the sac into surrounding tissue, causing painful inflammation and infection. Complete surgical removal is the only reliable fix.
Some stay unchanged for years and occasionally one shrinks after leaking, but the sac persists, so most cysts remain until removed. Uninflamed cysts that don't bother you can safely be left alone.
Epidermoid cysts are almost always benign, and turning cancerous is very rare. The bigger concern is misidentification — a lump that is hard, fixed, rapidly growing or bleeding should be examined promptly.
A minor procedure under local anesthetic: the clinician numbs the area, removes the entire sac through a small incision, and closes with a few stitches. Removing the whole sac is what prevents recurrence, and it's best done when the cyst isn't inflamed.
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