What are the possible reasons for swelling in my upper arm?

Possible reasons for upper arm swelling include:

Injury or trauma: Sprains, strains, bruises, or fractures can cause swelling. Infections: Skin infections like cellulitis or abscesses can cause redness, warmth, and swelling. Allergic reactions: Bites, stings, or contact with allergens can cause localized swelling. Blood clots (deep vein thrombosis): A clot in a vein may block blood flow and cause swelling. Lymphedema: Blockage or damage to lymph vessels, often related to surgery or radiation, can cause fluid buildup. Venous obstruction: Compression or blockage of veins can lead to swelling.

If swelling is sudden, worsening, painful, or accompanied by other symptoms such as fever or numbness, seek medical evaluation promptly.