A sebaceous cyst is a small, dome-shaped lump that develops just beneath the skin, made up of a sac filled with a thick, keratin-rich material. They feel firm, smooth, and slightly moveable when pressed, often described as feeling like a pea or marble under the skin. Many have a small dark central pore visible on the surface.

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Sebaceous cysts most commonly develop on the face, neck, scalp, chest, back, and shoulders, though they can appear almost anywhere on the body. They range in size from smaller than a pea to several centimetres across. They grow slowly and are extremely common, most people develop at least one in their lifetime.

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The two main types are epidermoid cysts (typically on the face, neck, chest, or shoulders) and pilar cysts (most often on the scalp, sometimes running in families). The term "sebaceous cyst" is now used as a general label, since most don't actually arise from the sebaceous glands themselves.

Sebaceous cysts are non-cancerous and generally harmless. However, unlike lipomas, they have a real tendency to become inflamed, infected, or rupture, releasing thick, often foul-smelling contents. Once a cyst has been infected, the surrounding capsule thickens, and removal becomes more difficult, which is why early removal of sebaceous cysts is usually recommended.

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We may recommend removal of a cyst if it is:

• Is causing pain, tenderness, or pressure

• Has been infected before, or keeps getting infected

• Is growing or has changed in appearance

• Is in a visible area and affecting your confidence

• Is catching on clothing, jewellery, or a comb

• Has features that warrant further investigation to rule out other conditions