What causes phlebitis?

Clot: Inside a vein occludes blood flow and then inflammatory process starts leading to pain and swelling leading to phlebitis

Phlebitis: Phlebitis is inflammation of a vein. itis means inflammation. Phleb means vein. Phlebitis can be from thrombosis (clot), also known as thrombophlebitis. Phlebitis can occur from injury, drugs (birth control pills), stasis or from thrombophilic disorders (genetic), among other causes.