What Causes a Sebaceous Cyst on the Scalp?

The term sebaceous cyst is commonly used for a rounded lump under the scalp, but many of these are epidermoid cysts rather than cysts arising from an oil gland. A cyst forms when skin cells move into a pocket beneath the surface and continue producing keratin. It may feel smooth, firm, or rubbery and may have a small central opening. Some remain quiet for a long time; others become inflamed after friction or bacterial contamination.

A scalp lump can also be a pilar cyst, lipoma, abscess, or another growth. Size and feel cannot establish the diagnosis, particularly if the lump is deep, fixed, or changing.

Do not squeeze, pierce, or cut the lump. Keep the area clean, avoid repeated pressure from combs or headwear, and arrange an examination if it is new or uncertain. A quiet cyst may only need observation. If it is inflamed, a clinician may discuss an intralesional steroid injection or, when infection and a collection are present, abscess drainage. Cyst removal can address the sac when recurrence or repeated irritation is a concern.

Seek prompt assessment if the lump becomes red, hot, rapidly larger, very tender, or begins draining foul-smelling material. Fever, spreading redness, or feeling unwell can signal a more extensive infection and needs urgent medical advice. Arrange routine review for a lump that persists, changes, bleeds, ulcerates, or interferes with washing or sleep. Do not assume every scalp lump is a cyst.

Does this lump look like an epidermoid or pilar cyst? Is it infected or simply inflamed? Would observation, injection, drainage, or cyst removal be appropriate, and what changes should prompt an earlier review?