The Difference Between Embolus and Thrombus

Both embolus and thrombus can pose a risk

Blood Clot
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An embolus and thrombus are similar in that they refer to blood clots. However, they have differences as well. An embolus travels through the bloodstream where it can cause a blockage. A thrombus is a blood clot in the vessel.

This article will go over what an embolus and thrombus, and which conditions cause them.

Embolus vs. Thrombus vs. Embolism

An embolus is a particle or mass (often a blood clot) that travels through the bloodstream. An embolus can get stuck in a blood vessel and block it, which causes organ damage. When organ damage is caused by an embolus, doctors will often say that an embolic event has occurred.

Sometimes, there can be more than one embolus. The plural of embolus is emboli.

thrombus is a blood clot that forms within a blood vessel. If a thrombus breaks free and travels through the bloodstream, it has become an embolus. Providers may refer to a thrombus that has become an embolus as a thromboembolism or simply an embolism.

Why Is an Embolus Dangerous?

When an embolus travels through the bloodstream, it is inevitably carried through smaller and smaller blood vessels until it gets stuck. Once lodged, it can obstruct further blood flow through that vessel.

The tissue being supplied by the blocked blood vessel then becomes starved for oxygen and nutrients (ischemic) and is likely to die. The larger the embolus, the larger the blood vessel it blocks, and the more tissue damage it can cause.

If a thrombus that has formed in a vein becomes embolized, it usually gets lodged in one of the pulmonary arteries where it can cause a pulmonary embolism.

If a thrombus forms in the arteries or on the left side of the heart (as in atrial fibrillation), and then becomes an embolus, it can end up damaging almost any organ in the body. It is a common cause of stroke.

However, an embolism can be treated. Anticoagulants (blood thinners) are often used to reduce the risk of tissue damage by thrombosis and emboli in people who are at increased risk.

Examples of Embolic Diseases

If you have certain diseases or medical conditions, you might be more likely to develop an embolus. Here are a few examples of embolic diseases.

  • A pulmonary embolus is an embolus (most typically, a blood clot) that travels to the lungs and produces lung damage. A pulmonary embolus is most often caused by deep vein thrombosis (blood clot formation) in the legs.
  • A cerebral embolus is an embolus that lodges in an artery supplying the brain, producing a stroke. A common cause of cerebral emboli is atrial fibrillation. In fact, a major goal of treating atrial fibrillation is to prevent embolic stroke.
  • fat embolus can occur when the fracture of a long bone releases fat droplets into the bloodstream. Fat emboli most often travel to the lungs or to the brain, producing pulmonary embolus or stroke.
  • A septic embolus is a mass of bacteria-containing tissue or pus that enters the bloodstream from a site of infection. Causes of a septic embolus include infectious endocarditis (an infection of one of the valves of the heart) or infection at the site of an intravenous catheter.
  • An air embolus is caused by small amounts of air that can get into the circulation during a medical procedure (such as surgery or a catheterization procedure).
  • cholesterol embolus is caused by the release of cholesterol crystals from an atherosclerotic plaque. These crystals can lodge in an artery downstream from the plaque and cause tissue damage. Cholesterol emboli most commonly occur with peripheral artery disease, and the damage they cause depends on the location of the plaque. Manifestations may include painful blue toes, gangrene of the lower extremities, skin discoloration, kidney failure, abdominal pain, intestinal bleeding, stroke, or peripheral nerve disease.
  • An amniotic fluid embolus is a rare emergency associated with childbirth. It is caused by amniotic fluid, or cells shed from the baby, entering the mother’s circulation through the placental bed. The damage done to the mother with an amniotic fluid embolus is usually not caused by the embolus lodging in a particular location, but rather, is caused by a general, often overwhelming, allergic reaction to “foreign” tissue. An amniotic fluid embolus is an extremely dangerous event that is often fatal.
  • A foreign body embolus is another rare event, usually associated with a medical procedure. For instance, talc entering the bloodstream can become an embolus.
  • “paradoxical” embolus is an embolus originating in a vein that ends up lodging in an artery. A paradoxical embolus requires a pathway from the right side of the heart to the left; for instance, via a patent foramen ovale.


An embolus is a particle or mass that flows through the bloodstream. A thrombus is a blood clot in a blood vessel. If a thrombus breaks off, it can become an embolus.

An embolus can produce tissue damage or death in almost any organ in the body. Lung damage (by a pulmonary embolus) and stroke (by a cerebral embolus) are two common conditions caused by emboli. 

Frequently Asked Questions

  • What is embolism?

    An embolism is a blood clot (thrombus) that breaks free and starts moving through the bloodstream. It is also called a thromboembolism.

  • How long do blood clots last?

    How long a blood clot lasts depends on many factors. If you are not taking any medications to thin your blood or receiving other treatment, a blood clot might not get broken down for weeks or even months.

  • Can embolism be treated?

    An embolism can be treated with medications that thin the blood. There are also some procedures that can be done to try to break up the clot.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  7. American Academy of Family Physicians. Deep Vein Thrombosis.

By Richard N. Fogoros, MD
Richard N. Fogoros, MD, is a retired professor of medicine and board-certified in internal medicine, clinical cardiology, and clinical electrophysiology.