What should you know about purple cyst under skin?

An epidermoid cyst is a sac beneath the skin that can contain keratin, a thick skin protein. If the cyst wall becomes inflamed or the area is pressed, the overlying skin may turn red, dusky, or purple. A cyst can be tender without being infected, but warmth, increasing pain, pus, or spreading redness raises concern for infection or an abscess. Other lumps can resemble a cyst, so the label should not be assumed from colour alone. The broader guide to [Skin Lumps](/symptoms/skin-lumps/) can help you describe what you notice.

Do not squeeze, puncture, or try to drain the lump yourself. Keep the skin clean and reduce pressure from clothing or bags. A clinician may observe a quiet cyst, use an injection such as [Steroid Injection Into The Skin](/treatments/injectables/intralesional-steroid-injection/) for selected inflammation, or recommend [Abscess Drainage](/treatments/minor-procedures/abscess-drainage/) when infected fluid needs release. [Cyst Removal](/treatments/surgical-dermatology/cyst-removal/) may be considered when the cyst repeatedly returns, remains troublesome, or needs definitive removal.

Arrange prompt assessment if the lump is rapidly enlarging, hot, very painful, draining, or surrounded by spreading redness. Seek urgent help for fever, chills, red streaks, severe swelling, or feeling faint. A new purple lump that does not settle, bleeds, or changes in firmness should also be examined rather than self-treated.

Does this feel like a cyst, abscess, or another lump? Is drainage needed, and would removing the cyst wall reduce recurrence? What symptoms mean I should return quickly?