Steatocystoma multiplex:
the oily skin cysts, what they are and how they are managed

What is steatocystoma?

A steatocystoma is a benign cyst that forms in the duct of a sebaceous gland, the oil gland attached to a hair follicle. Its thin wall is lined by cells that keep producing sebum, so the cyst fills with an oily, yellowish fluid rather than the cheesy keratin of more common skin cysts.

A single cyst is called steatocystoma simplex. Many cysts, often dozens and sometimes hundreds, are steatocystoma multiplex. A third form, steatocystoma multiplex suppurativa, describes cysts that repeatedly become inflamed, painful and discharge, and can leave scars. A 2025 review in Cutis described all three as benign cysts of the sebaceous follicle that usually cause no symptoms but can itch, hurt, become infected or scar.

Why it happens

Many cases run in families. A 2026 systematic review in Clinical, Cosmetic and Investigational Dermatology pooled 145 cases from 82 publications and found that changes in the keratin 17 gene (KRT17) were the most frequent genetic finding. Keratin 17 is a structural protein of the follicle wall, and faults in it are thought to weaken the follicle so that the duct balloons into a cyst. The same review found that about a quarter of cases were familial, and that familial cases began earlier. Hormones also matter: the cysts usually appear or multiply around puberty, when androgens switch on the oil glands.

Steatocystoma can also occur with no family history. In a few families, the same gene change causes thickened nails, a condition called pachyonychia congenita, so nail changes alongside the cysts are worth mentioning to a doctor.

What steatocystomas look and feel like

Steatocystomas are smooth, round, dome-shaped bumps under the skin, skin-coloured or yellowish, ranging from a few millimetres to over a centimetre across. They are usually soft to firm, move slightly under the skin and are not tender unless inflamed.

• Sites: the chest is the commonest site, followed by the underarms, upper arms, neck and, less often, the face, scalp, thighs and groin.
• Contents: if a cyst is punctured, it releases clear to yellow oily fluid, sometimes with fine hairs.
• Onset: the 2026 review found a median age at onset of 23 years and at diagnosis of 31 years, a delay of about eight years that reflects how often the cysts are mistaken for something else.
• Course: new cysts tend to appear slowly over years; existing ones can stay unchanged for a long time.

When cysts inflame, they become red, swollen and painful and may discharge, and in the suppurative form they can resemble hidradenitis suppurativa, a separate condition of the underarms and groin. The same review found hidradenitis suppurativa alongside steatocystoma more often in women than in men.

“A cyst that is only drained keeps its wall, and the wall is what refills. That is why removal means the lining, not just the oil.”

Dr Sin YongOn steatocystoma

Steatocystoma or something else? Cysts and bumps that look alike

Several common lumps look like steatocystomas, and the distinction changes what is done. Examination, the way a cyst feels and, when needed, the fluid or a small sample under the microscope usually sort them.

Small, firm cysts across the chest in a young adult are sometimes eruptive vellus hair cysts, a related condition that can occur alongside steatocystoma and is told apart under the microscope.

How steatocystoma is diagnosed

Steatocystoma is usually diagnosed from the pattern of many smooth, yellowish cysts on typical sites, a history of onset around puberty and, often, similar cysts in a parent or sibling. Confirmation, where it is needed, comes from looking at a removed cyst under the microscope.

• Examination: number, sites, size and whether any cysts are inflamed.
• History: when the cysts appeared, whether new ones keep forming, family history and any nail changes.
• Contents: oily fluid from a punctured cyst supports the diagnosis.
• Histology: the cyst wall shows a characteristic folded lining with sebaceous gland tissue within it, which separates it from an epidermoid cyst.
• Imaging: ultrasound is sometimes used when a lump's nature or depth is unclear.

A lump that is growing quickly, hard, fixed, bleeding or unlike the others is examined promptly and may need a biopsy, whatever the background of cysts.

Steatocystoma treatment options

Steatocystoma treatment aims to remove bothersome cysts together with their lining, because a cyst that is only drained keeps its wall and refills. Treatment does not stop new cysts forming, and cysts that cause no trouble can simply be left alone.

Published evidence is limited to small series. A 2014 study in Dermatologic Surgery described eight patients with multiple cysts treated by CO2 laser perforation followed by removal of the cyst wall with a small curette, and reported clinical improvement with minimal scarring and low recurrence. Any removal leaves a mark, and on the chest and shoulders, sites prone to keloid, that risk is weighed before treatment; see keloids and hypertrophic scars.

Squeezing or pricking cysts at home is not advised: the wall stays behind, the cyst refills, and the risk of infection and scarring rises.

How skin cysts are approached at this clinic

Every lump is examined in person before any treatment is discussed, because the right plan depends on what the lump is. At the clinic on Orchard Road, Singapore, Dr Sin Yong examines the cysts, asks about their history and family pattern, and explains which options are reasonable for their number, size and site, including leaving them alone.

• Inflamed or infected cysts are settled before any removal is considered.
• A lump that does not fit the pattern is examined further, with histology where its nature is uncertain.
• Where specialist dermatology or surgical care suits the situation better, for example extensive suppurative disease, referral is arranged; see second opinions and referral.

How a first visit runs is on the consultation process.

When to see a doctor about a skin cyst

See a doctor about a skin cyst when it is new and growing, painful, red or discharging, or when cysts are multiplying and affecting how you feel about your skin. Any lump that is hard, fixed, bleeding or changing quickly should be examined promptly.

• A cyst that becomes red, hot and painful, which suggests inflammation or infection.
• Many cysts appearing over the chest, underarms or arms, especially with a family history.
• Cysts with thickened or unusual nails.
• Recurring painful lumps in the underarms or groin, which may be hidradenitis suppurativa.
• A single lump that does not match the others.