In this guide16 sections
- Key Points
- What Is a Pilar Cyst (Trichilemmal Cyst)?
- What Does a Pilar Cyst on the Head Look and Feel Like?
- What Causes Pilar Cysts?
- What Else Could a Lump on Your Scalp Be?
- Is a Pilar Cyst Cancerous?
- When Should You See a Doctor About a Lump on Your Head?
- Can You Pop or Squeeze a Pilar Cyst?
- What Happens If a Pilar Cyst Bursts or Gets Infected?
- Can Pilar Cysts Go Away on Their Own?
- Pilar Cyst Removal: How Are Pilar Cysts Treated?
- Do Pilar Cysts Come Back After Removal?
- Can You Get Pilar Cyst Removal on the NHS?
- Frequently Asked Questions
- References
- Talk to a Surgeon About a Lump on Your Scalp
Key Points
- A pilar cyst, also called a trichilemmal cyst or, in older books, a wen, is a harmless lump filled with keratin that grows from the root of a hair follicle. About 9 in 10 are on the scalp.
- It feels smooth, firm and round, moves slightly under the skin and usually has no central pore. Many people have more than one, and pilar cysts often run in families.
- Pilar cysts are not cancer. Rarely, one starts to grow quickly and needs to be removed and examined, so see a doctor if a lump on your head grows fast, bleeds, breaks down or feels fixed.
- Squeezing or popping a pilar cyst does not get rid of it and can cause infection. Pilar cysts rarely go away on their own, and an infected cyst is settled first and removed later.
- Pilar cyst removal is a minor procedure under local anaesthetic that takes out the whole cyst with its lining. The scar is usually hidden once the hair grows back, you can wash your hair gently from day 3, and the stitches come out at 10–14 days.
- The NHS usually removes a pilar cyst only if it causes repeated infections, ongoing pain or problems with function, not because of how it looks.
Finding a lump on your scalp, often while brushing or washing your hair, is unsettling. In most adults the cause is a pilar cyst: a common, harmless cyst that grows slowly from a hair follicle. This guide explains what a pilar cyst is, what causes it, how to tell it apart from other lumps on the head, when a lump needs checking, and what pilar cyst removal involves, from the procedure itself to washing your hair afterwards.
If you are not sure what kind of lump you have, our guide to common skin lumps and bumps gives a wider overview.
What Is a Pilar Cyst (Trichilemmal Cyst)?
A pilar cyst is a closed sac under the skin, lined by the same cells that form the outer root sheath of a hair follicle. The lining keeps making keratin, the protein found in hair and nails, and because it has nowhere to go, it packs into a firm ball that slowly grows.
Doctors also call it a trichilemmal cyst (“tricho” means hair and “lemma” means sheath). The old English word for it is a wen. Pilar cysts grow where hair grows densely, so about 90% of them are on the scalp[1], although they can appear on the face, neck, back or limbs.
Pilar cysts are often called sebaceous cysts, and most lumps described as a sebaceous cyst on the head or scalp are in fact pilar cysts. The name is misleading, though. They are not filled with sebum, the oil made by the skin’s sebaceous glands, and they do not come from those glands. Our article on sebaceous cyst vs epidermoid cyst explains how the names became mixed up.
What Does a Pilar Cyst on the Head Look and Feel Like?
A cyst on the head is most likely to be a pilar cyst if it has these features:
- A smooth, dome-shaped lump under the skin, most often a lump on the top of the head (the crown) or on the back of the head.
- Firm and round, a bit like a marble or a pea under the skin when small, and like a golf ball when larger.
- Movable. It sits in the skin and the fat beneath it, so you can usually slide it a little over the skull.
- No central pore. Unlike an epidermoid cyst, a pilar cyst usually has no small dark opening (punctum) on top.
- Skin-coloured and painless, unless it becomes inflamed.
- Slow-growing over months or years, sometimes with several cysts appearing over time.
In a study of 27 people who had trichilemmal cysts removed, the median size was 21 mm, and people had noticed their cyst for a median of 18 months before it was taken out[3]. People with more than one cyst tended to be older and had larger cysts.
Are pilar cysts hard or soft?
Pilar cysts are firm, and many people describe one as a hard lump on the scalp or head. The keratin inside is packed more tightly than in an epidermoid cyst, and it often contains specks of calcium. In an ultrasound study of 54 trichilemmal cysts, 65% contained calcification, and cysts on the scalp were significantly more likely to have it[2]. Even so, a pilar cyst should still move a little and should not feel fixed to the bone. A lump that is rock-hard and does not move at all is more likely to be bone, which is covered below.
What Causes Pilar Cysts?
There is usually no outside cause. Pilar cysts are not caused by poor hygiene, hair products, diet or anything you have done, and they are not contagious. The main pilar cyst causes are:
- Genetics. Pilar cysts often run in families. A 2020 genetic study in Scientific Reports ↗ found that inherited pilar cysts are caused by changes in a gene called PLCD1, passed on in a dominant pattern, so a parent with the gene variant has a 1 in 2 chance of passing it to each child. The same study suggested that about a third of cysts that seem to be a one-off are in fact familial[4].
- Age. They usually appear in adults in middle age. In the ultrasound study the average age was 43[2], and in the surgical study it was 44[3].
- Hair-bearing skin. They grow from the root sheath of hair follicles, which is why the scalp is by far the most common site. Lumps on the face are more often other kinds of cyst, covered in our guides to eyelid lumps and the earlobe cyst.
Why do females get pilar cysts?
Studies consistently find slightly more women than men with pilar cysts: a ratio of about 1.3 women to every man in one series[2] and 59% women in another[3]. Nobody knows exactly why. The surgical study looked at headscarf use and hair thinning in women and found no link with either[3]. What matters more is family history: if a parent had pilar cysts, you are more likely to develop them, whatever your sex.
What Else Could a Lump on Your Scalp Be?
A pilar cyst is the most common reason for a lump on the scalp in adults, but it is not the only one. A doctor can usually tell them apart by examining the lump, and occasionally an ultrasound scan helps.
Pilar cyst vs epidermoid cyst
Epidermoid cysts are the most common skin cyst overall but are found mainly on the face, neck, chest and back. They often have a central pore and can leak soft, cheesy, strong-smelling material. Pilar cysts are firmer, usually have no pore and are mostly on the scalp. In a review of 324 cysts examined under the microscope, 89.8% were epidermoid and 8.9% were trichilemmal[5]. Both are treated the same way, by removing the cyst with its whole lining.
Pilar cyst vs lipoma
A lipoma is a lump of fat. It usually feels softer and more doughy than a cyst, although lipomas on the forehead and scalp can sit under the muscle layer and feel firmer than lipomas elsewhere. Our guide to lipoma vs cyst goes into the differences, and lipoma removal is a similar minor procedure.
Hard lump on the head that does not move: osteoma
An osteoma is a slow-growing lump of normal bone on the skull, most often on the forehead. It feels bone-hard, smooth and completely fixed. It is harmless but is removed differently from a cyst. Our guide to a hard lump on the forehead explains how to tell, and the forehead osteoma removal page covers treatment.
Lump on the back of the head: swollen lymph nodes
A lump on the back of the head, low down near the hairline, can be a swollen lymph node (gland). These are usually small, pea-sized and sometimes tender, and they swell in response to a scalp problem such as an itchy, flaky scalp, a skin infection, head lice or a recent cold. They usually settle within a few weeks once the cause clears. A gland that keeps growing, feels hard or fixed, or comes with fevers, night sweats or weight loss needs to be checked by a GP.
Bump on the head after hitting it
A tender bump that appears soon after you hit your head is usually a bruise or a collection of blood under the scalp, and it goes down over days to a couple of weeks. It is not a cyst. If you have hit your head and have a headache that is getting worse, are being sick, feel drowsy or confused, or have any problems with vision, speech or balance, seek urgent medical help through NHS 111, A&E or 999.
Lumps on the surface of the scalp
Growths on the surface rather than under it, such as raised moles, warty seborrhoeic keratoses or skin tags, are not cysts and are assessed through skin lesion removal. A scaly, crusted, bleeding or non-healing spot on the scalp, especially on sun-exposed or balding skin, should be checked for skin cancer, as our guide to an itchy or bleeding mole explains.
Is a Pilar Cyst Cancerous?
No. A pilar cyst is benign, meaning it is not cancer and does not spread. It does not turn into skin cancer in the vast majority of people.
There is one rare exception worth knowing about. In about 2% of trichilemmal cysts, the lining starts to multiply and the cyst grows into a larger, lumpier swelling called a proliferating trichilemmal tumour, or proliferating trichilemmal cyst[1]. These are mostly still benign, but they can grow quickly, break down on the surface and come back if not fully removed. Very rarely, one becomes malignant: malignant proliferating trichilemmal tumours make up less than 0.1% of all skin cancers[6].
This is the main reason a removed cyst is sent to the laboratory. As a 2023 review of 324 excised skin cysts in the Indian Dermatology Online Journal ↗ concluded, examining the tissue under a microscope is what confirms the diagnosis and picks up the rare unexpected change[5]. Our article can a cyst become cancerous? covers this in more detail.
When Should You See a Doctor About a Lump on Your Head?
A small, smooth lump that has been the same size for months and does not bother you is very likely to be a harmless cyst. It is still sensible to have any new lump on the head checked once by a GP or specialist so you know what it is. See a doctor sooner if the lump:
- is growing quickly, over weeks rather than months
- is larger than about 5 cm
- bleeds, breaks down into an open sore or will not heal
- feels hard and fixed rather than smooth and movable
- has become red, hot, swollen or painful
- has come back after it was removed
- comes with fevers, night sweats or weight loss you cannot explain
The NHS guide to skin cysts ↗ and the British Association of Dermatologists’ leaflet on epidermoid and pilar cysts ↗ are both good independent sources. Our article how do I know if a lump needs to be removed? sets out the warning signs for lumps anywhere on the body.
Can You Pop or Squeeze a Pilar Cyst?
It is not a good idea. Pilar cyst popping videos are popular online, but pilar cyst removal at home, whether by squeezing the cyst or piercing it with a needle, causes problems:
- It does not cure the cyst. Some keratin may come out, but the lining stays behind and fills up again.
- It can cause infection. Breaking the skin lets bacteria in and can turn a quiet cyst into a red, painful, swollen one.
- It makes removal harder. A cyst that has been squeezed or inflamed often becomes stuck to the surrounding tissue, so later removal needs a bigger cut and leaves a more noticeable scar, and it is more likely to come back.
Pilar cysts are also firmer and tighter than epidermoid cysts, so there is often no pore to squeeze through in the first place. Our article on whether you can remove a cyst at home explains the risks in more detail.
What Happens If a Pilar Cyst Bursts or Gets Infected?
A pilar cyst can burst under the skin after a knock, or after being squeezed. When the keratin leaks into the surrounding tissue, the body reacts strongly to it, and the area becomes red, swollen, hot and painful. This inflammation looks like infection but is often a reaction to the keratin rather than to bacteria. True infection can also happen, especially after squeezing.
An infected pilar cyst or a burst pilar cyst is not removed while it is inflamed, because the lining is hard to see and separate and the wound heals less well. Instead:
- A GP may prescribe antibiotics if there are signs of infection.
- A tense, painful collection of pus may need draining through a small cut.
- Once everything has settled, the cyst and its lining are removed through cyst removal so that it does not flare up again.
Get help urgently if redness is spreading quickly, you have a high temperature or shivers, or you feel very unwell: contact your GP or NHS 111, or call 999 if you feel seriously ill.
Can Pilar Cysts Go Away on Their Own?
Rarely. A pilar cyst can shrink for a while after it bursts, leaks or an inflamed episode settles, but the lining that makes keratin is still there, so the cyst usually fills up again. A small, stable cyst that does not bother you can simply be left alone and watched.
There is no cream, oil or pilar cyst shampoo that dissolves a cyst. Shampoos for dandruff or a flaky scalp can help the skin around a cyst, but they do not reach the sac under the skin. If you are wondering how to get rid of a pilar cyst for good, the only treatment that does it is taking out the whole sac.
Pilar Cyst Removal: How Are Pilar Cysts Treated?
Pilar cyst treatment means surgical removal, called excision. Draining a cyst empties it but leaves the lining behind, so it is used only to relieve an infected cyst, not as a cure. Pilar cysts tend to have a thicker, tougher wall than epidermoid cysts, so they often shell out in one piece, which makes removing the whole lining more straightforward.
How is a pilar cyst diagnosed?
A surgeon examines the lump, confirms that it behaves like a pilar cyst, and checks for any other cysts on the scalp. If the diagnosis is not clear, an ultrasound scan can be arranged. You will also be asked whether the cyst has ever been inflamed or drained, as this affects the technique and the scar.
How is a trichilemmal cyst removed?
Pilar cyst removal, also called trichilemmal cyst removal or scalp cyst removal, is a minor procedure done as a day case:
- The hair is parted and the skin over the cyst is cleaned and numbed with a local anaesthetic injection. You stay awake but should feel only pressure, not sharp pain.
- A small cut is made over the cyst, usually in line with the hair, and the cyst is freed and lifted out with its lining intact.
- The wound is closed with stitches and covered.
At Centre for Surgery, cyst removal usually takes 30–90 minutes depending on the size of the cyst. People with several pilar cysts can often have them removed in one visit: up to 4–5 small cysts are usually manageable under local anaesthetic, and for more, or for very large cysts, TIVA allows them to be removed together.
Recovery after scalp cyst removal: when can you wash your hair?
Recovery after scalp cyst removal is usually quick:
- The first day. A mild ache is common once the anaesthetic wears off after 2–4 hours, and it usually settles with paracetamol or ibuprofen. Most people go back to desk work the next day.
- From day 3. You can wash your hair gently with a mild shampoo, rinsing rather than scrubbing over the stitches, and patting the area dry.
- Days 10–14. The stitches on the scalp come out.
- 2–3 weeks. Leave strenuous exercise, swimming and saunas until the wound has healed.
Contact us if pain gets worse rather than better, redness spreads or you develop a fever.
Will removal leave a scar or a bald patch?
Any cut through the skin leaves a scar, but on the scalp it is usually a fine line that is hard to see once the hair grows back over it. Hair does not grow in the scar line itself, so if your hair is very short or thinning, it may show as a thin pale line. Our guide to types of scars explains how scars mature over the following months.
A large pilar cyst can stretch the skin over it, and the skin on top may look smooth and have fewer hairs. This is one of the main ways a pilar cyst causes hair loss. Removing the cyst takes the pressure off, and the hair around the scar usually looks normal once it has healed.
Is the removed cyst tested?
Every cyst we remove is examined by a pathologist. The result usually takes 3–4 weeks, and in almost every case it confirms a benign pilar cyst.
Do Pilar Cysts Come Back After Removal?
It is uncommon once the whole lining has been removed. A cyst is more likely to come back if it was drained rather than removed, or if the lining tore and a fragment was left behind. In a 2002 study of keratinous and pilar cysts removed through a small punch incision in Dermatologic Surgery ↗, the cyst came back in 3.6% of cases in the chart review and 8.3% in the patient survey, and just over half of those returns happened within the first year[7].
Pilar cysts often run in families, so new ones can appear elsewhere on the scalp over the years. These are new cysts, not the old one coming back. Our article will a cyst come back after removal? explains the difference.
Can You Get Pilar Cyst Removal on the NHS?
Usually only if the cyst is causing real problems. Under the NHS rules for removing harmless skin lumps, a pilar cyst can be removed when the diagnosis is clear and, for example, it has needed two or more courses of antibiotics in a year for repeated infection, it causes pain that needs regular daily medication, or it significantly affects function. Removal because of how a cyst looks or feels is not usually offered, as the Evidence-Based Interventions guidance on benign skin lesions ↗ sets out. The same rules cover moles, as our article on mole removal on the NHS explains.
Any lump where the diagnosis is uncertain, or which has worrying features, should be assessed on the NHS through your GP. If your cyst is harmless but you want it removed because it catches on your brush, is visible or keeps growing, private removal is the usual route.
Frequently Asked Questions
What is a wen on the skin?
“Wen” is an old word for a cyst under the skin, especially one on the scalp. Today it usually means a pilar (trichilemmal) cyst, although it was also used for epidermoid cysts. It is not a separate condition.
What is a pea-sized hard bump on my scalp?
In an adult, the most likely cause is a small pilar cyst, especially if it is smooth, round and moves slightly. A pea-sized bump low on the back of the head can also be a lymph node responding to an irritated scalp. Have it checked if it grows, becomes painful or is fixed in place.
Does pilar cyst shampoo work?
No shampoo can remove or shrink a pilar cyst, because the cyst sits under the skin inside its own sac. Products sold as pilar cyst shampoo may soothe a flaky or itchy scalp, but they do not treat the cyst itself.
Can a pilar cyst cause hair loss?
A small one does not. A large pilar cyst can stretch the skin on top so that it looks smooth and has fewer hairs over the lump. This is local to the cyst and usually improves once it is removed. A pilar cyst does not cause general hair thinning.
How big can a pilar cyst get?
Most are between about 1 and 5 cm. Left alone, some keep growing, and a cyst of 9 cm has been reported[1]. Larger cysts need a longer incision, so it is usually easier to remove one while it is still small.
Can I have several pilar cysts removed at once?
Yes. Many people with pilar cysts have more than one, and several can usually be removed in the same visit. Up to 4–5 small cysts are usually manageable under local anaesthetic, and TIVA can be used for more.
Are pilar cysts contagious?
No. You cannot catch a pilar cyst from someone or pass one on through contact, shared brushes or towels. The tendency to get them can be inherited, which is why they often appear in several members of the same family.
Is a pilar cyst dangerous?
No. Pilar cysts are benign. The risks are infection, especially after squeezing, and the rare proliferating change described above, which is why a lump that grows quickly or breaks down should be checked.
References
- Takamura N, Amo K, Yusa Y, Takezawa Y. A case of a giant trichilemmal cyst on the forehead. J Plast Reconstr Surg. 2023;3(1):21-25. doi:10.53045/jprs.2022-0044 ↗
- He P, Cui LG, Wang JR, et al. Trichilemmal cyst: clinical and sonographic features. J Ultrasound Med. 2019;38(1):91-96. doi:10.1002/jum.14666 ↗
- Işıktekin E, Kılıç S, Can B, Gözel B. Clinicopathological factors associated with trichilemmal cysts. JPRAS Open. 2025;48:137-146. doi:10.1016/j.jpra.2025.11.013 ↗
- Kolodney MS, Coman GC, Smolkin MB, et al. Hereditary trichilemmal cysts are caused by two hits to the same copy of the phospholipase C delta 1 gene (PLCD1). Sci Rep. 2020;10(1):6035. doi:10.1038/s41598-020-62959-z ↗
- Khullar G, Chandra M. Clinicopathological appraisal of cutaneous cysts: a 2-year retrospective observational study. Indian Dermatol Online J. 2023;14(6):844-848. doi:10.4103/idoj.idoj_239_23 ↗
- Lee DY, Han KM, Yoon JS. A malignant proliferating trichilemmal cyst arising on the elbow of a man: a case report and review of the literature. Medicine (Baltimore). 2023;102(25):e34035. doi:10.1097/MD.0000000000034035 ↗
- Mehrabi D, Leonhardt JM, Brodell RT. Removal of keratinous and pilar cysts with the punch incision technique: analysis of surgical outcomes. Dermatol Surg. 2002;28(8):673-677. doi:10.1046/j.1524-4725.2002.02020.x ↗
Talk to a Surgeon About a Lump on Your Scalp
If you have a lump on your scalp that you would like checked or removed, you can book a consultation at our Baker Street clinic by calling 020 7993 4849 or using the form below. A patient coordinator will be your point of contact throughout.
