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, you can check your symptoms to help identify possible causes and determine if you need prompt medical evaluation.