Why might one of my arms be swollen while the other is not?

Reviewed by Yoshinori Abe, MD

Internal Medicine

Swelling in one arm while the other stays normal is usually caused by a localized issue affecting that specific limb. Common causes include injury or trauma, infection (such as cellulitis), a blood clot (deep vein thrombosis), or lymphatic blockage (lymphedema). Less commonly, it may signal an underlying condition like a tumor pressing on blood or lymph vessels. Because one-sided arm swelling can range from minor to medically urgent, identifying the cause quickly matters.

Since symptoms overlap across many conditions—some harmless, some serious like blood clots—guessing isn't safe. A free, instant, online symptom check can help you clarify possible causes based on your specific symptoms and guide your next steps, whether that's home care or seeing a doctor promptly.

Reviewed for medical accuracy: 07/15/2026

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Explanation

Swelling in only one arm often points to a problem affecting that specific area, such as:

Injury: Sprains, fractures, or muscle strains can cause swelling in one arm. Infection: Localized infections like cellulitis cause swelling, redness, and warmth. Blood clots (deep vein thrombosis): A clot can block blood flow, leading to swelling and sometimes pain. Lymphedema: Blockage or damage to lymph nodes or vessels often causes swelling in just one arm, especially after surgery or radiation. Venous insufficiency or obstruction: Poor blood flow or vein blockage on one side can cause swelling. Allergic reactions: A bite or sting affecting one arm may cause localized swelling.

If swelling is sudden, painful, or accompanied by other symptoms like fever or chest pain, seek medical care promptly. For a personalized assessment of your arm swelling and related symptoms, try our free symptom checker to help identify potential causes.

(References)

Ciocon JO, & Galindo-Ciocon D. (1998). Arm edema, subclavian thrombosis, and pacemakers. Angiology, 9555935.
Coates GR, Clements JB, Yium J, & Watlington J. (1988). Painful edema of the arm after insertion of single-needle .... Southern medical journal, 3347860.
Geller BM, Vacek PM, O'Brien P, & Secker-Walker RH. (2003). Factors associated with arm swelling after breast cancer .... Journal of women's health (2002), 14670172.

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