Black cyst on the skin: what to check

An epidermoid cyst is often a rounded lump in or just below the skin and may have a visible central pore. A dark spot is not enough to distinguish a cyst from a dilated pore, inflamed follicle, abscess or another skin growth.

Keratin at a cyst opening can be exposed to air and mixed with skin debris, creating a dark plug. Rubbing, squeezing or spontaneous drainage can instead leave dried blood or a crust over the surface.

Inflammation can make a cyst red, tender and swollen even without infection. Increasing warmth, pus, spreading redness or feeling unwell raises concern for infection or an abscess and changes how the lump should be managed.

Leave the opening alone, wash gently and protect the bump from rubbing. A warm clean compress may soothe a tender closed lump, but it should not be hot enough to burn the skin.

Do not squeeze, pierce or attempt to pull out the dark plug. This can rupture the cyst wall under the skin, worsen inflammation and introduce bacteria. A clinician can decide whether observation, an injection, drainage or complete removal fits the diagnosis.

Seek prompt care if pain or swelling is rapidly worsening, redness spreads, pus drains, fever develops, the skin becomes very dark beyond the central pore, or the lump is near the eye and swelling affects vision.

Make a routine dermatology appointment if the diagnosis is uncertain, the lump returns after draining, repeatedly catches on clothing, grows, feels fixed or firm, bleeds without manipulation, or develops changing pigmentation.

Ask what features support a cyst diagnosis, whether active inflammation should settle before removal, whether drainage would leave the cyst lining behind, what scarring to expect from a procedure, and whether tissue should be examined after removal.