Swelling between the thumb and index finger without pain

The web space is made of muscle, connective tissue and skin that can appear fuller after gripping, exercise or a minor unnoticed knock. A small fluid-filled lump may feel smooth and change size. Tendon irritation around the thumb can cause swelling and may later produce pain with thumb movement; De Quervain's tenosynovitis is one condition a clinician may consider. Note whether the swelling is soft or firm, fixed or mobile, and whether the thumb feels weak, catches or moves less freely.

Compare both hands in the same position and take a simple daily note of size, activity and movement. Avoid repeatedly pressing or squeezing the area, and reduce tasks that require sustained pinching for a few days. Remove constricting jewelry. If the swelling remains, enlarges, becomes firm, or affects thumb use, book a clinical examination; do not try to drain a lump yourself.

Obtain prompt care if swelling develops quickly, becomes red or hot, follows an injury, or is joined by numbness, color change, weakness or difficulty moving the thumb. Fever or a wound near the area also raises concern for infection. A painless lump still needs timely review if it keeps growing or becomes fixed to deeper tissue.

Ask whether the swelling seems to involve a tendon, joint, muscle or cyst, whether imaging would clarify it, and how to modify work or exercise. Tell the clinician when it appeared and whether its size changes during the day.