What is a primary symptom of phlebitis?

Swelling and tenderness at the site is a primary symptom of phlebitis because this condition involves inflammation of a vein, typically resulting from irritation, injury, or infection. When the vein becomes inflamed, it often leads to localized symptoms such as swelling, pain, and tenderness in the affected area. These symptoms arise as the body's immune response is triggered, leading to increased blood flow and fluid accumulation in the tissues surrounding the inflamed vein. Recognizing these signs is crucial for timely intervention and management of phlebitis, which can help prevent complications like thrombosis.