A black lump on the leg

Dark colour may come from dried blood, bruising, a blocked skin opening, a blood-filled blister, a pigmented skin growth, or damaged tissue. Its appearance alone cannot show whether it is harmless, infected, related to circulation, or cancerous.

A clinician will check whether the lump sits in the skin or deeper tissue, whether it is firm or soft, and whether the surrounding leg is warm, swollen, numb, or discoloured. They may ask about an injury, insect bite, injection, recent surgery, diabetes, circulation problems, blood-thinning medicine, immune suppression, and any cancer history.

Some cancers can cause skin or soft-tissue lumps, and lymphoma can produce enlarged nodes, although a black leg lump is not enough to establish either diagnosis. Cancer of unknown primary describes cancer found after it has spread when the starting site has not yet been identified; it cannot be diagnosed from colour or location alone.

Arrange an appointment soon and take a clear photograph beside a ruler so changes can be compared. Record when the lump appeared and whether it is growing, draining, itching, or becoming tender. Keep it clean and protect it from friction with a dry, non-stick dressing if the surface is open.

Do not squeeze, puncture, cut, or apply corrosive wart remedies to the lump. If bleeding starts, press a clean pad firmly over it without repeatedly lifting the pad to check. Tell the clinician about fever, night sweats, unexplained weight change, or lumps elsewhere.

Seek same-day medical care if the black area is spreading, the lump rapidly enlarges, the surrounding skin becomes hot and red, pus appears, pain is severe, or fever develops. Use emergency services if bleeding will not stop with firm pressure, the whole leg suddenly swells, the foot becomes cold or numb, or you feel faint, confused, or short of breath.

Ask whether the lump arises from skin, blood vessels, or deeper tissue; whether imaging, a skin examination, or a biopsy is appropriate; and how to manage the surface while awaiting results. Clarify when a change should trigger an earlier return and whether any current medicine affects bruising, bleeding, or healing.