The medical term for this condition is thrombophlebitis. In it, small blood clots form in a vein of the legs and the vein becomes inflamed. This is usually caused by infection or injury.
Superficial phlebitis affects the veins visible just beneath the skin surface.
People who have varicose veins are susceptible, and the affected area will be red and swollen and feel warm, hard and tender to the touch. Usually amenable to home treatment, this type seldom results in clots that break loose and flow into the bloodstream. Deep vein thrombophlebitis, on the other hand, can result in a blood clot that breaks away from the wall of a vein forming an embolism. The clot can interfere with the circulation to the limb or ca use death if it reaches the lung. This type of phlebitis may occur after prolonged bed rest, major surgery, a heart attack or a stroke.