A sebaceous cyst is a small, non-cancerous lump that develops beneath the skin. It forms when a sebaceous gland or its duct becomes blocked. Sebaceous glands produce sebum, an oily substance that helps keep the skin and hair moisturised.
A sebaceous cyst is a slow-growing, non-cancerous lump beneath the skin. The term is commonly used to describe skin cysts, but most so-called “sebaceous cysts” are actually epidermoid cysts, which form from skin cells rather than sebaceous glands.
True sebaceous cysts arise from sebaceous (oil-producing) glands and are less common. In everyday medical practice, however, the terms are often used interchangeably. They are typically harmless and slow growing. Most do not require treatment unless they become painful, infected or bothersome.
Sebaceous and epidermoid cysts typically:
They are usually:
Many have a small central opening called a punctum, which represents the blocked follicle or gland. If the cyst ruptures, a thick, yellowish or white material may drain from the opening. The cyst contains a thick, oily or cheese-like material made up of sebum and keratin.
The contents are often described as having a strong or unpleasant odour due to the build-up of keratin and skin debris.
Most skin cysts form when:
Risk factors can include:
The trapped cells continue producing keratin, which accumulates within a sac under the skin.
True sebaceous cysts arise from sebaceous glands themselves, but these are uncommon compared to epidermoid cysts.
Most cysts are painless and cause no symptoms other than a visible lump beneath the skin.
Problems tend to arise only if the cyst becomes inflamed, ruptures or develops an infection. When this happens, the area may become red, warm and increasingly tender. Swelling can develop and the cyst may enlarge more quickly than usual. Infected cysts can release pus and may feel similar to a boil, often becoming more uncomfortable or painful over time.
Any cyst that changes suddenly, becomes painful or shows signs of infection should be assessed by a healthcare professional.
A sebaceous cyst is usually diagnosed by clinical examination. A GP or dermatologist will assess:
In most cases, no scans or tests are required. If there is uncertainty about the diagnosis, rapid growth, unusual features or concern about another condition, the cyst may be surgically removed and sent for histological examination to confirm the diagnosis. Imaging tests such as ultrasound are rarely required unless the lump is unusually large or located deeper under the skin.
Treatment is not always necessary. Many sebaceous cysts can be left alone if they are:
You should seek medical advice if the cyst:
Surgical removal is the most effective treatment. This is usually done under local anaesthetic. The entire cyst and its lining are removed to reduce the risk of recurrence.
If the cyst is infected, antibiotics may be prescribed. In some cases, the cyst may need to be drained before complete removal can be carried out.
Incision and drainage alone may relieve symptoms temporarily but does not remove the cyst wall, so the cyst may return. You should not squeeze or attempt to burst or pop a sebaceous cyst at home, as this can cause infection or scarring.
Surgical removal under local anaesthetic, with minimal scarring
Sebaceous cysts are benign and do not usually cause serious problems.
If completely removed, they are unlikely to return. However, recurrence can occur if part of the cyst lining remains.
Sebaceous cysts do not increase the risk of skin cancer. However, any lump that changes rapidly, bleeds without injury or behaves unusually should be assessed by a healthcare professional.
There is no guaranteed way to prevent sebaceous cysts.
General skin care measures may help reduce the risk of blockage:
If you notice a new lump or a change in an existing one, speak to a dermatologist for advice.
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