pulmonary embolism causes

February 12, 2026

Pulmonary embolism is usually caused by a blood clot that forms elsewhere in the body (most often in the deep veins of the leg) and then travels to the lungs, blocking a pulmonary artery.

What actually causes a pulmonary embolism?

In the vast majority of cases, a pulmonary embolism (PE) comes from a deep vein thrombosis (DVT) in the legs that breaks loose and moves through the bloodstream into the lung arteries.

Less commonly, clots can originate in deep veins of the pelvis or upper body, or in the right side of the heart, and embolize to the lungs.

In rare situations, PE can be caused by material other than a standard blood clot.

Air emboli – air bubbles entering the bloodstream (for example from certain medical procedures or trauma).
Fat emboli – fat droplets, typically after major long-bone fractures or severe trauma.
Tumor emboli – fragments of cancer tissue that travel to the pulmonary arteries.

These non‑clot causes are uncommon but important in specific clinical settings like severe trauma or advanced cancer.

Underlying mechanism: Virchow’s triad

Most causes and risk factors for pulmonary embolism can be understood through Virchow’s triad :

hypercoagulability (blood clots more easily),
venous stasis (sluggish blood flow),
endothelial injury (damage to blood vessel lining).

When more than one element of this triad is present—such as a person with cancer (hypercoagulable) who is also immobilized after surgery (stasis and vessel injury)—the risk of DVT and therefore PE rises sharply.

Major medical causes and risk factors

Conditions that make blood more likely to clot (hypercoagulable states)

Cancer, especially certain solid tumors and blood cancers (pancreatic, lung, gastric, brain, hematologic malignancies) significantly increase the risk of venous thromboembolism (VTE), which includes DVT and PE.

Inherited thrombophilias , such as factor V Leiden, prothrombin gene mutation, protein C or S deficiency, and antithrombin deficiency, make the blood more prone to clotting even at a young age.

Acquired thrombophilias , like antiphospholipid syndrome or conditions such as nephrotic syndrome and paroxysmal nocturnal hemoglobinuria, also promote abnormal clot formation.

Hormonal factors , including estrogen-containing birth control pills and hormone replacement therapy, raise clotting risk, especially in people who smoke or are overweight.

Pregnancy and the postpartum period create a naturally more pro‑coagulant state, increasing the likelihood of DVT and PE.

Infections and inflammatory states , including severe systemic infections, are recognized triggers for venous thromboembolism.

Situations that slow blood flow (stasis)

Prolonged immobility , such as long‑haul flights, extended car travel, long hospital stays, or being confined to bed, slows venous return from the legs and favors clot formation.

Recent surgery , especially orthopedic procedures (hip or knee replacements) and major abdominal or pelvic surgery, is a leading cause of postoperative DVT and subsequent PE.

Stroke, heart failure, or severe illness can confine a person to bed and reduce muscle pumping in the legs, increasing clot risk.

Traumatic hip fractures or joint fixation often involve immobilization of the lower limbs, which further increases the risk.

Damage to the vessel wall (endothelial injury)

Surgery and invasive procedures can directly injure blood vessels, creating a surface where clots can form.

Trauma, severe burns, and fractures damage tissues and vessels and trigger a cascade of clot-promoting signals.

Central venous catheters or other indwelling lines can irritate or injure veins and lead to upper‑extremity DVT that may embolize.

Lifestyle and chronic health contributors

Several chronic conditions and lifestyle factors don’t “cause” PE on their own but raise the background risk by interacting with the mechanisms above.

Advanced age – clot risk rises steadily with age as veins and clotting systems change and comorbidities accumulate.

Obesity – excess body weight is linked to higher VTE risk, especially when combined with immobility or estrogen use.

Smoking – tobacco use appears to increase clot risk, particularly in people who also have other risk factors like estrogen therapy or cardiovascular disease.

Chronic cardiovascular disease , including heart failure and prior myocardial infarction, is associated with a higher incidence of PE.

Diabetes and varicose veins are listed as associated risk factors in some clinical references, partly through vascular damage and altered blood flow.

Recent years have also highlighted severe COVID‑19 infection as a trigger for abnormal clotting throughout the body, including pulmonary embolism, particularly in hospitalized or critically ill patients.

HTML table: main causes and risk patterns

Below is an HTML-formatted table summarizing the core causes and risk patterns for pulmonary embolism:

html

<table>
  <thead>
    <tr>
      <th>Category</th>
      <th>Specific cause / setting</th>
      <th>How it leads to PE</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>Typical source of embolus</td>
      <td>Deep vein thrombosis (leg veins)</td>
      <td>Clot forms in deep leg veins, breaks off, travels through venous system and right heart to block pulmonary arteries.[web:1][web:3][web:5][web:9]</td>
    </tr>
    <tr>
      <td>Other thrombus sources</td>
      <td>Pelvic, upper-extremity, or right-heart thrombi</td>
      <td>Clots form in pelvic or arm veins or right heart, then embolize into pulmonary circulation.[web:1][web:3][web:9][web:10]</td>
    </tr>
    <tr>
      <td>Non-thrombotic emboli (rare)</td>
      <td>Air emboli</td>
      <td>Air enters venous system (e.g., trauma, procedures) and obstructs pulmonary vessels.[web:1][web:5][web:9]</td>
    </tr>
    <tr>
      <td>Non-thrombotic emboli (rare)</td>
      <td>Fat emboli</td>
      <td>Fat droplets from long-bone fractures or major trauma reach lung circulation and lodge in small arteries.[web:1][web:3][web:9]</td>
    </tr>
    <tr>
      <td>Non-thrombotic emboli (rare)</td>
      <td>Tumor emboli</td>
      <td>Fragments of malignant tumors travel via veins and block pulmonary arteries.[web:1][web:5][web:9]</td>
    </tr>
    <tr>
      <td>Hypercoagulability</td>
      <td>Cancer (pancreatic, lung, gastric, brain, hematologic cancers)</td>
      <td>Tumors release pro-coagulant factors, markedly increasing VTE and PE risk.[web:1][web:3][web:9]</td>
    </tr>
    <tr>
      <td>Hypercoagulability</td>
      <td>Inherited thrombophilia (e.g., factor V Leiden, prothrombin mutation, protein C/S or antithrombin deficiency)</td>
      <td>Genetic changes make clotting system overactive, promoting unprovoked DVT and PE.[web:3][web:9]</td>
    </tr>
    <tr>
      <td>Hypercoagulability</td>
      <td>Acquired thrombophilia (antiphospholipid syndrome, nephrotic syndrome, PNH)</td>
      <td>Acquired disorders alter clotting proteins or cell surfaces, predisposing to venous clots.[web:3][web:9]</td>
    </tr>
    <tr>
      <td>Hormone-related</td>
      <td>Estrogen-containing contraceptives or hormone replacement</td>
      <td>Estrogen increases clotting factors; risk is higher in smokers and people with other risk factors.[web:1][web:3][web:7]</td>
    </tr>
    <tr>
      <td>Hormone-related</td>
      <td>Pregnancy and postpartum</td>
      <td>Natural hypercoagulable state and reduced venous return from pelvic and leg veins increase DVT and PE risk.[web:3][web:5]</td>
    </tr>
    <tr>
      <td>Stasis / immobility</td>
      <td>Prolonged bedrest, paralysis, severe illness</td>
      <td>Reduced muscle pumping in the legs slows venous flow, encouraging clot formation.[web:1][web:3][web:9]</td>
    </tr>
    <tr>
      <td>Stasis / immobility</td>
      <td>Long-haul flights or long car trips</td>
      <td>Sitting still for many hours causes blood pooling in legs and can allow small clots to form.[web:1][web:3][web:5]</td>
    </tr>
    <tr>
      <td>Surgery and trauma</td>
      <td>Major surgery (especially orthopedic, abdominal, pelvic)</td>
      <td>Combines vessel injury, immobility, and systemic inflammatory response, making PE a common postoperative complication.[web:1][web:3][web:7][web:9]</td>
    </tr>
    <tr>
      <td>Surgery and trauma</td>
      <td>Major fractures, burns, or multiple trauma</td>
      <td>Cause endothelial injury and pro-thrombotic signaling; may also cause fat embolism in long-bone fractures.[web:1][web:3][web:9]</td>
    </tr>
    <tr>
      <td>Cardiovascular disease</td>
      <td>Heart failure, recent myocardial infarction, stroke</td>
      <td>Reduced mobility and altered hemodynamics create conditions for venous thrombosis and embolism.[web:1][web:3][web:9]</td>
    </tr>
    <tr>
      <td>Infection / inflammation</td>
      <td>Severe systemic infections, including severe COVID‑19</td>
      <td>Inflammation and endothelial activation promote abnormal clot formation in veins and pulmonary arteries.[web:7][web:9]</td>
    </tr>
    <tr>
      <td>Chronic / lifestyle</td>
      <td>Obesity, smoking, advanced age</td>
      <td>Increase baseline risk of VTE and interact with other risk factors like surgery or estrogen therapy.[web:3][web:7][web:9]</td>
    </tr>
    <tr>
      <td>Other associated factors</td>
      <td>Varicose veins, diabetes, pulmonary hypertension</td>
      <td>Associated with vascular damage and altered hemodynamics that may contribute to DVT and PE risk.[web:3]</td>
    </tr>
  </tbody>
</table>

“Quick Scoop” style takeaway

The core cause of pulmonary embolism is a clot—usually from a leg DVT—blocking blood flow in the arteries of the lungs.

The main background drivers are things that make blood clot more easily, slow blood flow, or damage vessels: cancer, surgery, immobility, hormonal changes, trauma, and certain inherited or acquired blood conditions.

Non‑clot emboli (air, fat, tumor) are rare but serious and typically arise in very specific situations like major trauma or advanced cancer.

Information gathered from public forums or data available on the internet and portrayed here.