Pulmonary embolism occurs due to damage to the vessel lining, stasis, and an increased tendency for blood clotting.

Cardiovascular diseases increase the risk of clot formation. Occupations requiring prolonged standing lead to varicose veins, which also increase clot risk.

Some medications increase blood clotting. Birth control pills can increase blood clotting rates.

Prolonged immobility, such as in bedridden individuals or during long journeys (e.g., over 4 hours), can cause clot formation and embolism.

There is an increased risk of embolism after certain surgeries, such as abdominal surgeries, leg surgeries, or surgeries involving general anesthesia and long durations, with the possibility of embolism occurring in the postoperative period.

Fat emboli can occur after liposuction.

In deep-sea divers, rapid ascent can lead to fat or air emboli, a condition also known as "the bends."

Cancer patients, particularly those with lung cancer, have a higher blood clotting rate and an increased risk of pulmonary embolism. Cancer patients undergoing chemotherapy also have an increased risk of clot formation.

Genetic predispositions can also increase blood clotting. Genetic factors such as Protein C deficiency, Factor V Leiden mutation, and antithrombin III deficiency can contribute to pulmonary embolism. Individuals with these genetic predispositions can develop clots at any age.

Smoking and obesity are also risk factors for pulmonary embolism.