Phlebitis refers to the inflammation of a vein. It describes the process when veins become swollen, bulging and inflamed due to blood clotting inside of the vein, or because the vein walls are damaged. Phlebitis can occur in both superficial veins that are closer to the skin’s surface, or deeper veins. These veins can become sore, red, itchy and tender, and may develop an infection if the blood clot is severe, leading to deep vein thrombophlebitis. Superficial phlebitis, which affects shallow veins is rarely serious, but may develop into Deep Vein Thrombophlebitis. This describes clotting in the larger and deeper blood vessels that usually rest in the legs. Large blood clots can form, which may break off and travel to the lungs. This is a serious condition called pulmonary embolism and requires immediate medical attention.