What causes an epidermoid cyst?

The sac is usually made from cells similar to those on the skin surface. Keratin, a thick skin protein, collects inside it, creating a rounded lump that may feel firm or move slightly under the skin. A small central opening or dark plug can sometimes be visible. These cysts are often called sebaceous cysts, although they do not usually begin in an oil gland.

A cyst may follow blocked skin cells, local injury or an inflamed hair follicle. It is not the same as an abscess, but it can become red, tender, swollen and foul-smelling if inflamed or infected. A new or changing Skin Lump should be examined when its identity is uncertain.

Do not squeeze, pierce or repeatedly massage the lump. A warm, damp compress may ease tenderness, but it does not remove the cyst wall. Keep the area clean and avoid friction from clothing or equipment. A clinician can discuss observation, a steroid injection into the skin for selected inflammation, drainage when a collection needs releasing, or Cyst Removal when removing the sac is appropriate.

Arrange an assessment if a lump grows, keeps returning, becomes painful, drains, changes colour or interferes with movement. Seek prompt care for spreading redness, increasing warmth, fever, red streaks or rapidly worsening pain. A clinician may need to distinguish a cyst from an abscess or another skin lump before choosing treatment.

Ask whether the lump is an epidermoid cyst, whether inflammation or infection is present, which treatment fits its current state, and how to reduce recurrence after any procedure.