The main symptoms are tenderness and pain in the area of the affected vein. Redness and/or swelling also may be seen. In the case of deep venous thrombosis, there is more swelling than is caused by superficial thrombophlebitis, and the patient may experience muscle stiffness in the affected area. There are many causes of thrombophlebitis.

The main causes can be grouped into three categories; injury to blood veins, increased blood clotting, and blood stasis. When blood veins are damaged, collagen in the blood vein wall is exposed. Platelets respond to collagen by initiating the clotting process. Damage to a vein can occur as a consequence of indwelling catheters, trauma, infection, Buerger's disease, or the injection of irritating substances. Increased tendency of the blood to clot can be caused by malignant tumors, genetic disorders, and oral contraceptives, though newer generation birth control pills carry a lower risk for many women. Stasis, in which the blood clots due to decreased blood flow in an area, can happen following surgery, as a consequence of varicose veins, as a complication of postpartum states, and following prolonged bed rest. In the case of prolonged bed rest, blood clots form because of inactivity, which allows blood to move sluggishly and stagnate (collect) in blood veins. This can lead to blood clots. These clots (also called emboli) sometimes are released when the patient stands up and resumes activity. This can present a problem if the emboli lodge in vital organs. In the case of postpartum patients, a fever developing four to 10 days after delivery may indicate thrombophlebitis. A 2004 study revealed that postmenopausal women taking hormone therapy combining estrogen and progestin had more than a twofold higher risk of venous thrombosis than non-hormone users.