Thrombophlebitis can cause painful swollen veins, according to Mayo Clinic. In addition, deep vein thrombosis (DVT) has the same effect.
Alongside causing pain and swelling, thrombophlebitis makes veins feel warm to touch. Some people also see hard red cords beneath their skin. Patients with DVT may not see the vein itself, but can experience pain and swelling in the leg if it is located there.
Patients who experience these symptoms should see a doctor immediately. People showing signs of DVT along with chest pain and shortness of breath should go to their local emergency room. Such symptoms indicate that a blood clot is present, which can travel to the lungs.