Phlebitis is swelling of a vein caused by a blood clot. It usually occurs in your legs. If the affected vein is just beneath the skin, the condition is usually not dangerous. A clot in a deeper vein, called deep vein thrombosis, can break loose and cause a serious problem in the lung, called a pulmonary embolism, or a heart attack or stroke.
Sitting still for a long time can make you more likely to get phlebitis. Some medicines and disorders that increase your risk for blood clots can also lead to phlebitis.
