What should you know about a large red lump on your arm?

Redness may reflect increased blood flow, irritation, or infection around the lump. A tender, warm area that expands can occur with a skin or soft-tissue infection. A firm, fixed, or steadily enlarging mass needs examination to identify its tissue of origin. A lump on the arm is not by itself a diagnosis of cancer.

A clinician may ask when it appeared, whether it followed an injury or injection, and whether you have fever, drainage, numbness, or reduced movement. Examination may be followed by ultrasound or another scan, with tissue sampling considered when the nature of the mass remains uncertain.

Arrange an appointment promptly, especially if the lump is growing, painful, warm, or present without a clear cause. Photographing the area and noting its approximate size, changes in colour, and associated symptoms can help your assessment.

Do not squeeze, puncture, or repeatedly massage it. Keep the skin clean, avoid friction from tight sleeves, and mention medicines that affect immunity or blood clotting. If an infection is suspected, treatment may involve prescribed medicine or drainage; a persistent solid mass follows a different pathway.

Seek urgent medical help if redness is spreading quickly, pain is severe, fever or chills develop, pus appears, the arm becomes very swollen, or you feel faint or unwell. Immediate assessment is also needed for new weakness, numbness, pale or blue skin, or difficulty moving the hand.

Ask what features suggest infection versus a solid mass, whether imaging is needed, and whether the lump should be sampled. You can also ask what changes should prompt earlier review and how to protect arm movement while the cause is being investigated.