When a vein is inflamed, the surrounding skin is red and hot, the vein becomes cord-like and swellings due to the accumulation of fluid in the tissue (oedema) may appear. As a result of the inflammation, blood components collect on the walls of the vein and form a blood clot that can be felt as a hard thread.

Phlebitis is generally caused by varicose veins but may also be triggered by injuries (knocks, punctures), allergies and other foci of inflammation in the body, e.g. badly infected tonsils.

Phlebitis can occur in the legs, arms and - very rarely - in other areas of the body (breast, neck, penis).

A specialist (phlebologist, angiologist, vascular surgeon, dermatologist) needs to be consulted straightaway, because phlebitis of superficial veins can spread to the deep vein system and then cause a dangerous occlusion or deep venous thrombosis.