What could cause right arm swelling without pain?

Swelling without pain can still indicate an underlying issue. Some possible causes include:

Lymphedema: A buildup of lymph fluid due to damage or blockage in the lymphatic system—often after surgery or radiation. Venous insufficiency: Poor return of blood from the arm to the heart may lead to fluid pooling and swelling. Blood clot (deep vein thrombosis): Although DVT often causes pain, it can sometimes present with swelling only. Mild injury or overuse: Repetitive motion or a minor strain may cause swelling without noticeable pain. Allergic reaction: Swelling from an insect bite, sting, or mild allergic response may not be painful. Mass or tumor pressing on veins or lymphatics: Rarely, a growth can block drainage in the arm, leading to painless swelling.

Even without pain, ongoing or unexplained swelling should be evaluated—especially if it increases, spreads, or is accompanied by changes in skin color or sensation.