An epidermoid cyst is a firm lump under the skin, lined with the same cells as the skin surface and slowly filling with keratin. It is harmless and often sits quietly for years. The trouble starts when the wall ruptures, which is why squeezing one is the worst thing you can do to it. A keratin-filled cyst arising from the hair root sheath, usually on the scalp.
The same eight facts on every condition comparison.
Round lump Smooth and movable under skin.
Central opening A small dark pore on top.
Inflamed cyst Red, swollen and tender.
Pilar Cyst Parted hair reveals a smooth raised bump beneath the skin.
A sac lined by skin-like cells forms beneath the surface and fills with shed keratin. If the lining ruptures, escaped keratin can provoke inflammation in the surrounding tissue.
Cells from the hair root sheath form a cyst lining beneath the skin. Keratin produced by this lining accumulates inside the cyst.
Epidermal Inclusion Cyst. Most often develops in adults, though it can occur at other ages.
Pilar Cyst. Most often recognised in adults.
An epidermal inclusion cyst forms when surface skin cells get trapped under the skin and keep making keratin.
Keratin accumulates within a cyst lined by cells from the hair root sheath.
Evidence labels come from each condition’s own treatment list.
A small injection of steroid into an inflamed cyst early in a flare, which settles the swelling and pain over a few days. It is for the flare, not the cyst — the sac and its lining are still there afterwards. It works best in the first day or two, before the lump has come to a head.
The only thing that ends a cyst, because it takes out the sac wall as well as the contents. It is a single minor procedure under local anesthetic, done through a small cut that is usually placed along a natural skin crease. Done on a quiet cyst it lifts out whole and leaves a thin line; done on an inflamed one it tears, fragments get left behind, and it is more likely to come back.
Incision and drainage. A small cut to let out the contents of a large, painful, inflamed cyst. The relief is immediate and it is exactly the right thing to do for an abscess. It is not a cure: the lining stays behind and keeps making keratin, so it usually refills over weeks to months. The usual plan is to settle things this way, then remove the sac properly a month or two later.
Can remove a symptomatic or troublesome cyst and its wall; the specimen may be examined.
Left alone, a cyst sits quietly for years, punctuated by flares. The pattern matters more than any single episode - a cyst that has never flared can come out whenever it suits you, while one that has flared twice is on a trajectory. Plan removal during a quiet spell.
Pilar cysts are usually benign and often remain unless removed. A painful or inflamed cyst needs assessment; recurrence is possible if the cyst wall is not completely removed.
Rupture and a painful flare
The wall tears and keratin spills into the tissue around it, and the immune system attacks it. The lump becomes hot, swollen and painful over a day or two, and feels bigger and firmer than it did. Most of these are not infections. Squeezing is the single most common reason it happens, so leaving a quiet cyst alone is the best prevention there is.
Infection or an abscess
Sometimes bacteria do get in, and the cyst becomes a genuine abscess. It looks much like an ordinary flare, so the things that point to infection are spreading discoloration, pus, fever and feeling unwell. This is the version where antibiotics belong, and a large abscess usually needs draining as well. A hot, inflamed cyst around the nose, eyes or upper lip is treated more cautiously than one anywhere else.
Scars and keloids from repeat flares
Every rupture and every emergency drainage lays down its own scar, and after a few episodes the area is tethered and marked before anyone has operated. Raised, thickened scars and keloids are more likely on the chest, shoulders, upper back and jawline, and more likely on deeper skin tones. A planned removal on a quiet cyst usually leaves a thin line along a natural skin crease, which is the argument for doing it sooner.
Most are benign; a rapidly growing, ulcerated or recurrent lump needs assessment.
Seek assessment if a lump is growing, recurrently inflamed or uncertain. Rapidly increasing pain, redness, drainage or fever may require prompt treatment.
Have painful, growing, bleeding or uncertain lumps examined.
Epidermoid cysts are benign. They do not spread and do not turn into cancer. Cancers arising inside a cyst are described but genuinely rare. Have it examined if it grows rapidly, feels hard and fixed rather than mobile, bleeds, or has a sore over it that will not heal - those suggest the lump may not be a cyst.
The contents are keratin and broken-down skin cells, sealed in for a long time, and skin bacteria break that material down. The smell comes from the contents, not from infection.
You can, and for a large, painful, inflamed cyst that is the right thing for relief. But draining empties the contents and leaves the lining, and the lining makes keratin, so it refills over weeks to months. Removing the whole sac is what ends it.
Because the result is worse. Inflamed tissue is swollen and fragile, so the sac tears instead of lifting out whole, fragments get left behind, the cyst is more likely to come back, and the scar is wider. Settle the flare first, then remove it a month or two later.
Not if the whole lining comes out, which is the goal. Recurrence happens when a fragment is left behind, more likely if the cyst was inflamed or heavily scarred from previous flares. New cysts can form elsewhere - that is a new cyst, not the old one.
Not reliably, because most people who get one have no identifiable cause. You can reduce flares - do not squeeze them, take pressure and friction off them, and treat significant acne if cysts keep appearing where it was. If you are getting a lot from a young age, mention it, because a few people have an inherited reason.
A keratin-filled cyst arising from the hair root sheath, usually on the scalp.
Avoid picking or squeezing and protect it from comb trauma.
Have painful, growing, bleeding or uncertain lumps examined.
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